VTechWorks Repository :: Browsing by Author "Kok, Loke T."

Browsing by Author "Kok, Loke T."

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Assessing Eucryptorrhynchus brandti as a Potential Carrier for Verticillium albo-atrum from Infected Ailanthus altissima
Snyder, Amy Lynn (Virginia Tech, 2011-05-20)
Significant mortality of the invasive tree of heaven (TOH), Ailanthus altissima (Mill.) Swingle, was first observed in Pennsylvania in 2002 to be caused by an apparently host-specific strain of Verticillium albo-atrum Reinke & Berthold, a soil-borne, vascular wilt fungus. A limited survey conducted in Virginia revealed two sites where TOH stands were infected with V. albo-atrum. A virulence test confirmed that fungal isolates from both states were found to be highly pathogenic on TOH, killing all inoculated seedlings in 9 weeks. After overwintering, 11% (n = 37) of TOH root sections tested positive for V. albo-atrum, although the origin of the colonies was not identified. The pathogenicity of this pathogen suggests that it could be used together with host-specific insects for the biological control of TOH. A host-specific herbivorous weevil from China, Eucryptorrhynchus brandti Harold (Coleoptera: Curculionidae) that has been extensively studied as another potential biological control agent for TOH is currently pending quarantine release. Quarantine experiments were conducted to test different forms of transmission with E. brandti and V. albo-atrum simultaneously. In one experiment, 75% (n = 32) of adult E. brandti transmitted V. albo-atrum to TOH seedlings after walking on an actively growing culture and feeding on infected plant material. In another study after feeding on infected TOH stems for 24, 48 and 72 h, respectively, 16.7% (n = 120), 15.0% and 12.5% of adult E. brandti ingested and passed viable V. albo-atrum propagules into feces. Surviving weevils (83%, n = 20) overwintering in infested potting mix carried viable V. albo-atrum propagules externally. In addition, all weevil progeny that emerged from infected TOH billets appeared to be as healthy as weevils reared from non-infected billets and wild parents from China. Results from these laboratory studies indicate E. brandti has the ability to spread V. albo-atrum from tree to tree in a laboratory setting.
Assessing performance and compatibility of three Laricobius species as predators of hemlock woolly adelgid, Adelges tsugae
Story, Heather Marie (Virginia Tech, 2010-05-19)
Predation, egg production and survivorship of Laricobius nigrinus Fender, L. rubidus, LeConte, and L. osakensis Montgomery and Shiyaki (proposed), predators of hemlock woolly adelgid, Adelges tsugae, Annand, were investigated in the laboratory and in the field. In individual assays, L. rubidus oviposited fewer eggs than either L. nigrinus or L. osakensis. In assays containing congeneric or conspecific groups of adult Laricobius, L. osakensis preyed upon the greatest number of ovisacs. When all three species were together, the numbers of ovisacs preyed upon were similar to the mean of all three individual species. Adult predators fed on few eggs and did not exhibit any species preference. The numbers of A. tsugae ovisacs fed upon did not differ significantly by groups of congeneric or conspecific Laricobius larvae. Laricobius adults and larvae had high survival rates throughout all experiments. In the field, predators were enclosed in sleeve cages with both high (> 120 ovisacs) and low (< 90 ovisacs) A. tsugae densities for 1 wk. All branches with caged beetles had significantly greater numbers of ovisacs preyed upon than branches caged without beetles. No differences in predation or egg production were found among the conspecific and congeneric groupings. Predation was uniformly higher at the high prey-density than at the low prey-density. Survivorship among predators did not differ significantly at either prey density. Results from both laboratory and field experiments suggest that these species are able to co-exist and can be in the same location for biological control of A. tsugae.
Behavior and daily activity patterns of specialist and generalist predators of the hemlock woolly adelgid, Adelges tsugae
Flowers, Robbie Wayne; Salom, Scott M.; Kok, Loke T.; Mullins, Donald E. (University of Arizona, 2007-08-14)
The behavior and daily activity patterns of two specialist predators, Laricobius nigrinus Fender (Coleoptera: Derodontidae) and Sasajiscymnus tsugae, Sasaji and McClure (Coleoptera: Coccinellidae), and a generalist predator, Harmonia axyridis Pallas (Coleoptera: Coccinellidae), of hemlock wooly adelgid, Adelges tsugae (Hemiptera: Adelgidae), were examined using digital video recording in the laboratory...
Biological and ecological studies of Hydrotaea aenescens (Wiedemann) (Diptera: Muscidae), and other arthropods of high-rise cage layer poultry houses
Dillon, Perian Lenore (Virginia Tech, 1994-05-15)
Laboratory and field studies of Hydrotaea aenescens were undertaken to provide information on this predator's biology and ecology under differing conditions, and to promote its use as a biocontrol agent for controlling house flies in poultry houses. Taxonomic diversity of arthropods in a new high-rise cage layer poultry house was determined from manure samples collected from different manure moisture categories. Stabilization of taxonomic diversity and taxonomic evenness of manure-inhabiting arthropods occurred after the house had been operating for eight months. In contrast, overall diversity in high-rise poultry houses at a well managed, longer established farm was significantly higher than that observed at the new farm, even after 1 1/2 years of operation. When the densities of selected manure-inhabiting predatory arthropods collected from the manure samples (including Carcinops pumilio, pseudoscorpions, a dermapteran species, an anthocorid species, and H. aenescens) were correlated with percent manure moisture, the results showed that, of these predators, only H. aenescens was positively correlated with both manure moisture and with densities of house fly larvae. This information emphasized that although predators such as C. pumilio may exhibit high predation rates on house fly eggs and first instars, their effectiveness 1s reduced by their spatial separation from their supposed prey. This contrasts greatly with H. aenescens performance. Decreases in survival of house fly larvae occurred when the larvae were exposed to H. aenescens of higher larval stadia. This was dramatically demonstrated when 100 first instar house flies were exposed to 100 second instar H. aenescens. No house fly larvae survived. Developmental times were determined at constant temperatures for egg, and larval H. aenescens. Developmental times decreased as temperature increased. Median time for egg and larval development ranged from 1.3 and 14.6 days at 22.2°C to 0.5 and 8.3 days at 35.0°C, for the respective stages. All of this information, together with developmental times and mortality of H. aenescens immatures gathered in a study of temperature dependent development has enhanced understanding of the biotic interactions in accumulated poultry manure. These data will be invaluable in designing integrated pest management programs especially in the area of computer-aided decision making.
Biological control agents of soybean insect pests in the Tidewater area of Virginia
Eaton, Alan Tucker (Virginia Tech, 1975-01-05)
The species of biological control agents which affect soybean pests in the Tidewater area were investigated, and their relative values were determined. Two pentatomids, Podisus Macu1iventris Say and Stiretrus anchorago F., were the only significant bio-contro1 agents which attacked the Mexican bean beetle, Epi1achna varivestis Mulsant. Thesepredators were not able to hold the pest population in check. A parasitic fly, Trichopoda pennipes F. was the only important biological control agent which attacked the green stinkbug, Acrosternum hilare (Say). Host and habitdt preferences of the fly suggested the presence of two strains in Virginia. Distribution of the fly was very uneven. Fungal disease was found to be an important control agent of many (larval) Lepidoptera. It was the most important control agent of Plachypena scabra (F.). P. scabra was also controlled by predation and parasitism. Nine parasites attacked the larvae and pupae. No effective biological controls were found for the corn earworm, Heliothis zea (Boddie). The only significant control agent, fungal disease, acted too slowly to prevent economic damage by this insect.
Biological control for the public
Kok, Loke T.; Kok, Vicki (Kok, L.T., 1999)
Despite the successful use of biological control in the control of insects and weeds for over a hundred years, this concept is still not very well known among the general public. Even in major universities, the concepts and methodology of biological control are not taught in the more general introductory courses, but only in specialized courses that usually have small enrollment. Consequently, less than 10 percent of the students attend classes that include the concept of biological control. This lack of knowledge of biological control among students, growers, and the general public throughout the State of Virginia is readily perceived in my dealings with them during the past 27 years. Very few are aware of the valuable potentials of biological control as a pest problem solving technique, or of the availability of research information on the topic. This unfortunate situation can be readily rectified through a more effective method of dissemination of information. To achieve this goal, the National Biological Control Institute (NBCI), United States Department of Agriculture (USDA), Animal and Plant Inspection Service (APHIS) has provided funds for this project to make biological control information more readily accessible. The objective of this project is to develop a program that provides information on the general principles and methodology of biological control in a format that is easily accessible in a compact disc (CD). Included are examples of biological control of weeds and insect pests, with color images of selected examples. This CD will be made available at minimal cost, to all interested individuals or groups, such as schools, county agents, foresters, 4-H, environmental groups, master gardeners, farmers, landowners, and highway departments. To complement this effort, a website on biological control containing information on insects and weeds and their natural enemies will also be established. This website will be continuously updated so that currency of information will be maintained.
Biology and Host-Range Testing of Laricobius kangdingensis sp. n. (Coleoptera: Derodontidae), a Newly Discovered Predator of Hemlock Woolly Adelgid, Adelges tsugae Annand (Homoptera: Adelgidae)
Gatton, Holly A. (Virginia Tech, 2005-04-25)
The biology and host-specificity of Laricobius kangdingensis sp. n. (Coleoptera: Derodontidae), a new predator of hemlock woolly adelgid (HWA), Adelges tsugae Annand (Homoptera: Adelgidae) were investigated and compared with that of a related predator of HWA, L. nigrinus Fender. Adults became active in June 2003; the males emerged first and in greater numbers than the females. The sex ratio of female to male was 1: 1.1. Laricobius kangdingensis sp. n. has four larval instars. The total number of eggs laid between 7 July 2003 and 7 August 2004 was 1327. Mean lifetime fecundity per female was 196.4 ± 53.4 eggs and 97.9 eggs for the P1 (parental gen.) and F1 generations, respectively. In comparison, lifetime fecundity for F1 L. nigrinus was 100.8 ± 89.6 eggs. Developmental rates were studied in fall 2003 and spring 2004. Combined with data gathered previously at 12 and 15ºC in early 2003, the 6, 9, and 18ºC data were used to determine lower temperature development thresholds for the egg (2.8ºC), larval (1.6ºC), and pre-pupal (5.8ºC) stages. The egg and larval thresholds are lower than those observed for L. nigrinus. Laricobius kangdingensis sp. n. individuals completed development only at 12 and 15ºC; however, these adults did not emerge from aestivation after pupation. Laricobius kangdingensis sp. n. appears to be host-specific. In paired-choice feeding tests, adults consumed significantly more HWA than two other adelgid species [eastern spruce gall adelgid, Adelges abietis (L.), and pine bark adelgid, Pineus strobi (Hartig)], the pine needle scale, Chionaspis pinifoliae (Fitch), and the woolly alder aphid, Paraprociphilus tessellatus (Fitch). In paired-choice oviposition tests, females laid more eggs on HWA-infested eastern hemlock than on any other test prey. In no-choice host suitability experiments larvae fed on HWA; eastern spruce gall adelgid; the larch adelgid, A. laricis Vallot; the balsam woolly adelgid, A. piceae (Ratzeburg); pine bark adelgid; and pine needle scale, but not on woolly alder aphid or elongate hemlock scale, Fiorinia externa Ferris. Although no larvae completed development in any of the bioassays, 6 out of 15 larvae (40%) in the HWA treatment reached the pre-pupal stage. One larva out of 6 reached the pre-pupal stage on pine bark adelgid.
Biology of Laricobius nigrinus Fender (Coleoptera: Derodontidae) and its potential as a biological control agent of the hemlock woolly adelgid, Adelges tsugae Annand (Homoptera: Adelgidae) in the eastern United States
Zilahi-Balogh, Gabriella M. G. (Virginia Tech, 2001-11-09)
The biology of Laricobius nigrinus Fender (Coleoptera: Derodontidae) and its potential for control of hemlock woolly adelgid (HWA), Adelges tsugae Annand (Homoptera: Adelgidae) in the eastern United States were investigated. Laricobius nigrinus completed development on HWA in laboratory studies. There are four larval instars. Mean larval consumption was 225.9 and 252.3 HWA eggs at 12 and 18 °C, respectively. Post-aestivation activity period was 36.6 and 30.8 weeks for males and females at 13 °C, respectively. Mean lifetime fecundity was 100.8 eggs over a mean ovipositional period of 13.2 weeks. Laricobius nigrinus is host specific. In paired-choice and no-choice oviposition tests, L. nigrinus laid more eggs in HWA ovisacs than other test species. Laricobius nigrinus consumed more eggs of HWA than eggs of Adelges piceae (Ratzeburg) and Pineus strobi (Hartig) but not of Adelges abietis (L.). In larval development tests, L. nigrinus only completed development on HWA. A two-year field study conducted in British Columbia showed that: 1) the life cycle of HWA in British Columbia is similar to that previously reported in Virginia and Connecticut; 2) L. nigrinus adults undergo an aestival diapause that coincides with the diapause of the first instar HWA sistens. Adult activity beginning in autumn coincides with resumption of development of the sistens generation; 3) oviposition and subsequent larval development of L. nigrinus coincide with oviposition by HWA sistens adults. Temperature-dependent development was determined for egg, larval, pre-pupal and pupal stages of L. nigrinus at five constant temperatures (9, 12, 15, 18 and 21 °C). Development time was inversely proportional to temperature between 9 and 18 °C. Laricobius nigrinus did not complete development at 21 °C. Minimum developmental temperatures for eggs (6.5 °C), larvae (5.1 °C), pre-pupae (3.8 °C), and pupae (3.1 °C) were determined by extrapolation of linear regression equations to the x-intercept. Degree-days calculated for eggs, larvae, pre-pupae, pupae, and egg to adult were 54.6, 161.3, 196.1, 212.8, and 666.7, respectively. The laboratory derived degree-day model for predicting egg hatch was validated with field data collected in British Columbia. Observed median egg hatch at three of four sites over two years was within 15% of the predicted DD value (54.6).
Competitive interactions among two specialist predators and a generalist predator of hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae)
Flowers, Robbie Wayne (Virginia Tech, 2006-04-10)
Competitive interactions among two specialist predators, Laricobius nigrinus Fender (Coleoptera: Derodontidae) and Sasajiscymnus tsugae Sasaji and McClure (Coleoptera: Coccinellidae), and a generalist predator, Harmonia axyridis Pallas (Coleoptera: Coccinellidae), of hemlock woolly adelgid were evaluated using laboratory, field and video studies. The two specialist predators are part of a biological control program for A. tsugae, and the potential for competition among these species and previously established generalist predators is unknown. In laboratory studies of predator groups in Petri dish assays, the only significant negative effects from competition occurred among conspecifics, resulting in reduced net egg production by L. nigrinus and H. axyridis and reduced feeding by H. axyridis. In contrast, heterospecific combinations showed non-interference. In longer duration field studies of predator groups, held in branch enclosures, predator survival and feeding were not significantly affected by additional predators. Net reproduction was again significantly reduced by conspecifics, while heterospecifics showed non-interference for all predator responses. All predators reduced the number of A. tsugae nymphs of the next generation relative to no-predator controls; however, L. nigrinus had much greater impact overall due to the large number of progeny produced. Video studies revealed that predator behavior varied qualitatively and quantitatively by species, and did not appear to be coordinated temporally or spatially. All species exhibited continuous activity patterns that were punctuated by longer periods of rest. The specialist predators were more selective of feeding and oviposition sites, and rested at more concealed locations than H. axyridis. Conspecifics significantly altered the time allocated to specific behaviors for L. nigrinus and H. axyridis, resulting in reduced predator effectiveness due to increased searching and decreased feeding and oviposition. All predator groups maintained a high degree of spatial separation relative to assay size, suggesting that chemical or tactile cues may be used to regulate their distributions. Overall, these studies suggest that the three predator species will be compatible in this system. Management implications include using multiple-predator species combinations over single-species for biological control of A. tsugae and implementing low-density releases to reduce the potential negative effects of intraspecific competition.
Contributions toward the integrated pest management of diamondback moth, Plutella xylostella (L.), on collards in Virginia
Cordero Alonso, Roberto J. (Virginia Tech, 2005-10-19)
Diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae) is a serious pest of crucifer vegetables (Brassica sp.) worldwide because of a lack of effective natural enemies in certain regions and because of insecticide resistance. In 2003, laboratory and field studies were initiated in Virginia to better understand P. xylostella, its primary natural enemies, and their susceptibilities to insecticides in order to develop an economically and environmentally sound integrated pest management program for collards in the state. Ecological life table studies of P. xylostella immature stages on collards located on the Eastern Shore and on Kentland Farm, near Blacksburg at the New River Valley, VA revealed that most (98 to 99%) of P. xylostella died from natural causes. Mortality factors varied between the two regions. Neonates, small larvae, and large larvae disappearing were major mortality factors. Rainfall, predation, and dispersal probably contributed the most to this mortality. Egg mortality played a bigger role at the New River Valley compared with the Eastern Shore. Three parasitoid species were found that contributed to the mortality of P. xylostella: Diadegma insulare (Cresson) (Hymenoptera: Ichneumonidae); Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae); and Microplitis plutellae (Muesebeck) (Hymenoptera: Braconidae). Additional studies conducted in the laboratory using leaf-dip bioassays revealed that P. xylostella collected from the Eastern Shore of Virginia, showed significant tolerance levels to esfenvalerate, acetamiprid, methomyl, methoxyfenozide, indoxacarb, and acephate compared with a susceptible strain of P. xylostella. The highest tolerance ratio (1,876 fold) was to esfenvalerate, a commonly-used pyrethroid. All of the insecticides tested in this study were quite toxic to the adult stage of the parasitoids, D. insulare and O. sokolowskii. The insect growth regulator, methoxyfenozide was considerably less toxic than other insecticides such as esfenvalerate, methomyl, acephate, spinosad, indoxacarb, and emamectin benzoate at field-rate and 1% of field-rate concentrations. The aforementioned insecticides as well as some other insecticides were evaluated several times in the field for efficacy against P. xylostella as well as other pests of collards. The most efficacious insecticides over five field experiments included acephate, emamectin benzoate, esfenvalerate, methomyl, methoxyfenozide, novaluron, indoxacarb, and spinosad. These insecticides were followed in relative efficacy by Bt kurstaki, acetamiprid, and azadirachtin, which provided relatively inconsistent control of lepidopteran larvae over the experiments. Effective insecticide options in collards that are less toxic to natural enemies and that can fit well into integrated pest management programs include indoxacarb, spinosad, novaluron, emamectin benzoate, methoxyfenozide, and Bacillus thuringiensis subsp. kurstaki.
Developing methods of strip cropping cucumbers with rye/vetch
Ogutu, Maurice Okendo (Virginia Tech, 2000-11-20)
The purpose of this research carried out in 1998 and 1999 was to develop methods for strip cropping of cucumbers with rye/vetch and black plastic mulch. Effects of planting methods, weed control measures, and cover crop management techniques on pest and beneficial insects, petiole sap nitrate-nitrogen, soil moisture, yields and economic viability were assessed. Four treatments, namely cucumber direct seeded in black plastic mulch on tilled bare ground (conventional); cucumber direct seeded in black plastic mulch laid over incorporated rye/vetch residue; cucumber direct seeded into no-till rolled rye/vetch; and seedlings transplanted into no- till rolled rye/vetch, were evaluated in a randomized complete block design. Weeds were controlled in half the plot by critical manual weeding and pre-emergence herbicides applied in the other half in all treatments except the conventional system. Three-week interval staggered plantings of buckwheat to provide flowers for adult beneficial insects were also evaluated. Results obtained indicate that rye/vetch habitat is more attractive to beneficial insects than cucumber beetles before rolling or flail mowing. There were higher densities of adult Diptera (an indicator for Tachinid parasitoids) in both years and of Pennsylvania leatherwings in 1999 in plots with rye/vetch than in plots with rye only before planting. Preferential attraction to adult Diptera was not found after planting with no differences in cumulative densities between no-till and black plastic mulch plots after rolling or flail mowing. However, adult Diptera densities were positively correlated with cucumber yield, higher densities of cucumber beetles occurred in black plastic mulch than in no-till plots in both years, and bacterial wilt, transmitted by cucumber beetles, was reduced in no-till in 1999. Similarly, rye/vetch habitat plots had a higher diversity of Carabidae species (in both habitat areas and crop rows) before rolling or flail mowing, and higher densities of Carabidae (in habitat areas), Staphylinidae (in both habitat areas and crop rows) and spiders (in crop rows) after rolling or flail mowing. Black plastic mulch plots with flail mowed, incorporated rye/vetch residues had higher petiole sap nitrate-nitrogen and higher early season cucumber plant dry weights than in conventional plots; later in the season, the highest petiole sap nitrate-nitrogen occurred in no-till plots. No-till had higher marketable cucumber yield than plastic systems. The profitability of these production systems depended more on differences in marketable yield than on cost differences. The plastic with incorporated rye/vetch and no-till transplant systems were more profitable during early harvests in late July, while no- till direct seeded and transplant systems were more profitable from early August onwards. The three-week interval staggered planting of buckwheat led to conservation of beneficial insects, and the second and third seeded buckwheat flowering periods coincided with the period vetch had lost flowers.
Development of a Precision Mite Management Program for the Control of the Ectoparasite Varroa destructor in Hives of Apis mellifera L.
Means, Jackson C. (Virginia Tech, 2014-06-03)
The European honey bee, Apis mellifera, is an important pollinator of horticultural and agricultural field crops, providing ≈ 90% of all commercial pollination services (Genersch et al. 2010). The recent rise in colony loss due to Colony Collapse Disorder (CCD) has been a source of concern for both beekeepers and the apiculture industry. One of the factors implicated in CCD is infestation by the ectoparasitic mite, Varroa destructor. Initial efforts to control the mite relied heavily on regular application of miticides without regard to actual mite infestation levels. This approach has led to problems of resistance in the mite and contamination of the hive and hive-products. Because it is unlikely that miticides will be removed as an option for mite management, a precision mite management (PMM) approach using information on the spatiotemporal distribution of the mite to improve sampling and treatments is seen as a viable option, particularly with respect to treatment costs and impacts on the environment. The primary objective of this study was to develop an understanding of the spatiotemporal distribution of the Varroa mite and bee brood within hives for the purpose of developing a PMM approach for the mite. Varroa mite populations were sampled from May to June, 2012 and February to October, 2013. Sampling was conducted with three commonly used sampling methods: soapy water roll (SWR), brood uncapping, and a modified sticky board; brood uncapping, however, was discontinued during the study due to hive the labor cost and harmful effects of this method to the hives. Similar trends in mite population levels were observed using the soapy water roll and sticky board sampling methods. Spearman's nonparametric analysis showed that there was a significant correlation (ρ = 0.47, P<0.001) in mite population levels for the soapy water roll and sticky board methods for sampling conducted from February to September, 2013 (the SWR method was not used in October). This was despite the fact that there was no significant correlation (ρ= -0.03, P = 0.8548) between the two sampling methods during the spring sampling period from February to April, 2013. The observed lack of correlation between the two sampling methods in early spring was likely due to the low population of brood in the hive, which caused the majority of the mites to remain on adult bees. Mites per 100 adult bees, therefore, appear to reflect mite population levels within the hive more closely than mite fall on sticky borad during the February to April sampling period. This suggests that the soapy water roll method is a better method for estimating mite population levels within the hive in the early spring compared with the sticky board method. Geospatial analyses of the distributions of mite fall on the sticky boards were conducted using geostatistics and Spatial Analysis by Distance IndicEs (SADIE). Both analyses showed that mite fall on the sticky board was generally aggregated and the aggregation increased with mite population levels. The average range of the variogram from geostatistical analysis was estimated at 4 sticky board cells; this range value was increased to 5 cells and was used to develop a systematic outside-range sampling protocol for mites on a sticky board. The results showed that the accuracy of the systematic outside-range sampling compared well with that of the traditional sticky board counting method in estimating total mite fall, but required only 60% of the effort (i.e., counting 63 instead of 105 cells). SADIE analysis showed that there is an overall association between the distribution of mite fall on a sticky board and the distribution of brood within a hive. A greater degree of correspondence was also observed in the association of drone and mite distributions during May to June; greater correspondence in worker brood and mite associations was observed in August and September. These differences may be due to relative amounts of the two types of brood present within the hive. A test of the efficacy of precision application of Varroa mite treatment based on the association between drone brood and mite fall resulted in a significantly greater reduction in mite levels on the sticky board using a traditional miticide treatment method compared with the control and precision treatments (𝜒2 =362.571; df = 2; P <0.0001); mite population levels with the precision method, however, were significantly reduced compared with the control.
Developmental and reproductive ecology of Melanoplus femurrubrum (De Geer) and some other melanopline grasshoppers (Orthoptera, Acrididae)
Bellinger, Robert Glenn (Virginia Polytechnic Institute and State University, 1985)
The red-legged grasshopper, Melanoplus femurrubrum femurrubrum (De Geer), was found to be developmentally polymorphic. Local field populations in Virginia had five, six, seven, and eight instars, determined by antennal segment counts. Adults with five instars were uncommon, and six and seven-instar adults were the most abundant morphs. Laboratory studies showed that decreasing temperature decreased both the number of instars, and developmental rate. Grasshoppers with fewer instars had the differential number of instars deleted from between the third and penultimate instars, thus, temperature must affect instar number early in the life cycle, i.e., before the third instar. The laboratory study produced no five-instar grasshoppers. Most individuals had six or· seven instars, depending on temperatures. Few eight-instar individuals were produced in the laboratory. Grasshoppers with more instars had longer developmental times and larger body sizes. Females were larger than males and tended to go through more instars, however, males and females which developed with the same number of instars did not differ in developmental time. In field populations, instar number was positively correlated with accumulated heat units the month of hatch, but body size was negatively correlated. Mean population in Melanoplus spp. grasshoppers is positively correlated with mean species body size. In the laboratory, ovariole number in M. femurrubrum was related to the size of the egg from which the female hatched, and in field populations mean population ovariole number in was determined by mean length of the growing season, and rainfall in the maternal generation. In field populations number of pods laid was less than two, and was related to rainfall in September, while pod size was related to body size and rainfall in October. Numbers of pods laid and total eggs were negatively correlated with the tegmen/femur ratio.
Ecological and logistical considerations toward introducing Heringia calcarata to New Zealand
Gresham, Sean Daniel Morehu (Virginia Tech, 2013-04-22)
This thesis outlines research conducted as part of a collaborative project between Virginia Tech and Plant and Food Research New Zealand (PFRNZ) to introduce Heringia calcarata (Loew) (Diptera: Syrphidae) to New Zealand (NZ) for biological control of woolly apple aphid (WAA), Eriosoma lanigerum (Hausmann) (Hemiptera: Aphididae). Ultimately, the introduction of H. calcarata to New Zealand will be contingent upon satisfying regulatory requirements and concerns, including documentation that it will not have an adverse effect on the existing biological control of WAA by Aphelinus mali (Haldeman) (Hymenoptera: Aphelinidae). As well, it will be critical to develop methods for sustained rearing of H. calcarata in captivity. Basic and applied studies were conducted toward providing essential information for advancing this project. Apple shoot sections with a WAA colony that did or did not contain mummified aphids parasitized by A. mali were deployed in pairs at the base of apple trees. There was no significant difference in the mean number of H. calcarata eggs deposited between shoots with parasitized (1.5 ± 0.34 SE) and non-parasitized colonies (1.75 ± 0.42 SE), although female H. calcarata laid eggs less frequently on colonies with a high percentage parasitization. In choice-test feeding studies, larvae were offered non-parasitized aphids in combination with aphids in an early stage of parasitization or mummified aphids. Larvae consumed significantly fewer aphids in an early stage of parasitization (10.8 ± 0.48 SE) than non-parasitized aphids (13.4 ± 0.42 SE) and very few mummies (0.4 ± 0.14 SE) compared with non-parasitized aphids (14.2 ± 0.4 SE). In no-choice feeding trials, larvae consumed significantly more non-parasitized aphids (25.3 ± 1.93 SE) than aphids in an early stage of parasitization (19.7 ± 1.85 SE) or mummified aphids (2.2 ± 0.71 SE) and significantly fewer mummified aphids were consumed than early parasitized aphids. WAA colonies in situ on the branches of potted apple trees were exposed to H. calcarata, A. mali, or both. Exposure to H. calcarata larvae independently and in combination with A. mali was shown to have a significant effect on the number of WAA compared with control colonies, and H. calcarata larvae did not affect the number of mummified aphids produced within colonies. Heringia calcarata eggs were collected by deploying excised apple shoot sections containing at least one WAA colony at the base of apple trees for 8-12 h. One or more eggs were laid on 29% of shoots (n = 233 shoots). On shoots with eggs, 2.4 ± 0.21 SE eggs per shoot were recorded. In 2012, four shipments of H. calcarata eggs and larvae (total of 178) were sent from Virginia to a quarantine containment facility in NZ. This demonstrated that juvenile H. calcarata could be successfully transported internationally. In total, 124 adult flies were generated in NZ, representing 69.9% of the number of eggs and larvae recovered upon delivery to quarantine. Field-collected gravid female H. calcarata oviposited on WAA colonies under captive conditions: 63% in 2011 (n = 8) and 80% in 2012 (n = 15). In 2012, 98% of the eggs deposited hatched. Virgin females reared from eggs in the laboratory developed mature oocytes regardless of access to pollen. The findings of this research offer valuable insights into the biology and ecology of H. calcarata that are directly relevant to the project goals and that will help guide the development of H. calcarata as a classical biological control agent for WAA in NZ.
Ecological studies and pesticide response of Evergestis rimosalis (Guenee) (Lepidoptera: Pyralidae) and its parasitoid Cotesia orobenae Forbes (Hymenoptera: Braconidae)
Acosta-Martinez, Jaime A. (Virginia Tech, 1995-10-14)
The effects of temperature on emergence, development, oviposition, longevity and fecundity of Cotesia orobenae Forbes (Hymenoptera: Braconidae) were studied. Development time of parasitoid pupae decreased as temperature increased to 35°C. Temperatures between 20 and 25°C were most suitable for parasitoid development, oviposition and fecundity. Longevity was significantly affected by temperature, and was greatest between I5 and 20°C for both sexes. Sex ratios obtained from virgin females, females mated once and females exposed to multiple mating were compared. Virgin females produced only males, those with single or multiple mating produced more females than males. Cotesia orobenae exposed to five densities of third instar cross-striped cabbageworm, Evergestis rimosaiis (Guenee) (Lepidoptera: Pyralidae), for 24 h showed differences in percent parasitization among the treatments. The highest number of parasitoid cocoon masses was obtained from a density of 10 hosts.
Ecology, behavior, impact, and an integrated pest management strategy for the orangestriped oakworm, Anisota Senatoria (J. E. Smith), in the urban landscape
Coffelt, Mark Alan (Virginia Tech, 1992-06-01)
The biology of Anisota senatoria J. E. Smith (Lepidoptera: Saturniidae) was examined through ecological studies of within-tree distribution and dispersion, and the influence of a tree growth regulator on development and survival. Biological characteristics examined egg mass size and development, pheromone attraction, response to blacklight traps, adult emergence, laboratory development, pupal mortality and comparison of first versus second generation development time, fecundity and amount of infestation. Within-tree distribution of life stages showed significant differences between low (1.7-3.6 min height), middle (3.7-5.5 m) and high (5.6-7.6 m) strata. Dispersion indices generated from Taylor’s power law showed aggregation was greatest among early instars, followed by third instars and late instars. A fixed level precision sampling plan was developed based on the number of eggs and early instars present in low strata. The tree growth regulator paclobutrazol significantly reduced Q. Phellos L., willow oak, growth, especially one and two years posttreatment. One year posttreatment, paclobutrazol treatments significantly slowed development and decreased survival of early instars, but the opposite relationship was found with late instars. Behavior studies showed that increased A. senatoria survival occurred with increased group size. Laboratory and field experiments revealed critical group sizes for survival of 1-3 larvae and between 25-50 larvae. Anisota senatoria defoliation impact and frass were measured. Growth and root starch were significantly reduced with increased defoliation in Quercus palustris Muench., pin oak, but Q. phellos root starch was not reduced. Reduction in starch content in Q. palustris may have been related to additional stress factors. Landscape fabrics were a reliable sampling method for frass. Frass was used as a method for differentiating larval instars and predicted defoliatioonf Q. palustris. An integrated pest management (IPM) program was developed that included information on native parasites, host plant preference, a citizen survey, and aesthetic indicators. Four egg parasite species including an Aprostocetus new species, five larval parasites and eight hyperparasites were collected. Host plant preference experiments indicated that Q. alba L., white oak, was least preferred by A. senatoria. A citizen survey provided a framework for designing an IPM program. Monitoring and establishing an aesthetic injury level of 25% defoliation decreased pesticide volume without an attendant increase in damage. The number of egg masses (threshold) that caused 25% defoliation ranged from one to nine.
The effect of spirea aphid (Homoptera: aphididae) feeding and nitrogen fertilization on the growth of young apple trees, with comparisons to apple aphid
Kaakeh, Walid (Virginia Tech, 1989-06-03)
The overall goal of this research was to determine the effects of spirea aphid, Aphis spiraecola Patch, feeding and nitrogen fertilization on net photosynthesis (Pn), leaf chlorophyll content and greenneess, growth, dry matter accumulation, and carbohydrate concentrations of young apple trees, with comparisons to apple aphid, Aphis pomi DeGeer. Trees were artificially infested and grown in an unheated greenhouse with screened ends. The spirea aphid responded differently to various nitrogen treatments. Aphid density increased at a faster rate on trees receiving higher nitrogen application. The leaf nitrogen concentration increased significantly and linearly with increasing amount of urea application in both infested and control leaves. Also, a significant difference in leaf nitrogen concentration was found at each urea application rate between infested and control leaves. Spirea aphid feeding and sooty mold accumulations caused significant reductions in photosynthetic rates, leaf chlorophyll content, and greenness. Pn increased linearly with increasing chlorophyll content and greenness; nitrogen rates caused an increase in Pn and leaf greenness. Aphid-days accumulations were strongly correlated to Pn and greenness at each nitrogen rate applied. Accumulation of callose at the phloem sieve plates in response to spirea aphid feeding occurred but to a lesser degree than from other aphids reported on apple and pecan leaves. Accumulation of fresh and dry weights in all tree parts (leaves, lateral shoots, trunk, rootstock, and roots) during the growing season were affected by both spirea aphid and nitrogen fertilization. The spirea aphid reduced accumulation of fresh and dry weights in all tree partitions when trees were harvested at the end of the first growing season. These reductions were still lower than the control when trees were harvested at the ten-leaf stage the following spring. The spirea aphid caused a significant reduction in lateral shoot growth at the end of the growing season and at the ten-leaf stage. Fresh and dry weights of all tree partitions tended to increase with increasing rates of nitrogen. The percentage and the amount of nonstructural carbohydrates (NSC) in all tree partitions were reduced by spirea aphid feeding and were positively related to nitrogen rate. At the ten-leaf stage in the second season, similar results were obtained. Development of spirea aphid and apple aphid was similar on trees fertilized with a moderate rate of nitrogen. Pn and leaf greenness declined to a similar extent with accumulated aphid-days, for both aphid species. Aphid species did not affect any of tree growth or NSC accumulation.
Efficacy of Entomopathogenic Nematodes and Entomopathogenic Fungi against Masked Chafer White Grubs, Cyclocephala spp. (Coleoptera: Scarabaeidae)
Wu, Shaohui (Virginia Tech, 2013-05-07)
Entomopathogenic nematodes (EPN) (Heterorhabditis bacteriophora and H. megidis) and entomopathogenic fungi (EPF) (Metarhizium anisopliae and Beauveria bassiana) were evaluated for efficacy against masked chafer white grub, Cyclocephala spp., under laboratory and greenhouse conditions, as well as their efficacy against various grub stages in the field. Under both laboratory and greenhouse conditions, additive interactions were found between EPN and EPF in their combined application against Cyclocephala spp., except a few observations that showed antagonism or synergism. Significantly greater control occurred from the combination of a nematode and a fungus compared with a fungus alone, but not compared with a nematode alone. The combined effect did not differ significantly for nematode and fungi applied simultaneously or at different times. EPF had no significant impact on EPN infection and production of infective juveniles (IJs) in grub carcasses. Nematodes alone or in combination with fungi were comparable to the insecticide Merit 75 WP (imidacloprid) against 3rd instar Cyclocephala spp in the greenhouse. Efficacy of EPF and EPN varied dramatically between field sites and conditions; EPN and EPF applied alone or in combination were less effective than Merit 75 WP in >50% field trials, but some EPN + EPF treatments were more effective than the insecticide in reducing grub numbers. EPN and EPF showed better potential than insecticides for providing extended control of white grubs in the subsequent generation. In addition, the sub-lethal effects of EPF on southern masked chafer, C. lurida, were investigated. Neither M. anisopliae nor B. bassiana had a sub-lethal effect on grub weight gain, adult longevity, oviposition, pupation and eclosion. Finally, interaction between H. bacteriophora and M. anisopliae was examined to determine the potential of the nematode in improving fungal distribution in soil. H. bacteriophora enhanced fungal distribution in sandy loam soil without grass thatch, but not in sandy soil with thatch. In both soil types, soil depths significantly affected nematode and fungal distribution. In water profile, M. anisopliae conidia germinated hyphae that attached to sheath of H. bacteriophora IJs, which molted to detach from the fungus. IJs mortality and virulence were not affected by the presence of M. anisopliae.
Enhancing the weaver ant, Oecophylla smaragdina (Hymenoptera: Formicidae), for biological control of a shoot borer, Hypsipyla robusta (Lepidoptera: Pyralidae), in Malaysian mahogany plantations
Lim, Grace T. (Virginia Tech, 2007-04-04)
The weaver ant is a promising biological control agent of a shoot borer, Hypsipyla robusta Moore, on mahogany, but techniques to conserve ant colonies redistributed to mahogany plantations have not yet been developed. The effect of food supplementation and host plant species preference of the weaver ant, Oecophylla smaragdina F., was evaluated in a series of field studies. A simple model was developed to estimate the number of ants within nests on Khaya ivorensis A. Chev. (Meliaceae): log₁₀ (Number of ants) = - 1.16 + 1.09 log₁₀ (Nest size). Nest size is calculated from estimated nest height (ĥ) and length (Ã ) using the formula = π;r²⁺; Ã , where r = Â½ ĥ. This model was useful for repeated assessments of ant population levels to evaluate treatment effects. It provides better estimates than previous indirect methods based on nest counts and ant trail counts on plant parts. Colonies that were relocated without their queens and very small colonies (< 10,000 ants) failed to establish on new host trees, indicating that a minimum ant population and queen needs to be transferred for colony survival. Established colonies consumed more high-protein foods (live mealworms and fish) than high-carbohydrate liquid foods (honey and –weaver ant formula–, which contained sucrose and human muscle-training powder (Enerpro™)). Relocated colonies consumed more weaver ant formula and as many mealworms as established colonies, indicating that existing and relocated colonies require different food supplementation strategies. Decreasing consumption over time and preferential consumption among high-protein food choices (i.e., of mealworms over fish) indicated that ants select and regulate food consumption based on colony needs. Therefore, food supplementation should be as needed. Preliminary indications were that self-sufficiency in trophobiont (honeydew) levels may be achieved in two months after colony relocation. The optimal colony density that would protect K. ivorensis was estimated to be within the range of 6 – 48 colonies per ha based on previous reports for cocoa and cashew, and a consideration of the low damage threshold for mahogany. Substituting chemical control with weaver ants at those application rates gave similar IRRs (Internal rate of return; 11.6 – 12.2 vs. 12.0%) in preliminary financial analyses, and was preferable from an ecological standpoint. Twenty-nine host plant species were found for Malaysian O. smaragdina, of which 11 were new species records for Oecophylla spp. Also, there were two new genera and eight new species records for Malaysian O. smaragdina. Of eight trophobiont families collected, six species were identified, yielding new trophobiont-host plant species records for four coccoid species and two membracid genera. Screening of several ant-abundant plant species that included preliminary pest risk analyses for trophobionts on K. ivorensis, identified M. citrifolia as a promising candidate for mixed-planting with this mahogany species.
Evaluating the suitability of Laricobius nigrinus Fender (Coleoptera: Derodontidae), a biological control agent for hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae)
Lamb, Ashley B. (Virginia Tech, 2005-04-20)
Hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae), is an introduced pest injurious to hemlock trees (Tsuga spp.) in the eastern United States. HWA currently infests hemlock in over 50% of its geographic range and has the potential to spread throughout its entire range. Since HWA populations in the eastern United States are not regulated effectively by natural enemies (Wallace and Hain 2000), classical biological control is the most promising option for controlling this pest in the forest setting. This work evaluates Laricobius nigrinus Fender (Coleoptera: Derodontidae), a predator associated with HWA in western North America, is being evaluated as a potential biological control agent for HWA (Cheah et al. 2004). Observations suggest that natural enemies may help keep HWA populations below injurious levels in the western United States (Mausel, pers. comm.). Laboratory studies have revealed that L. nigrinus feed selectively on HWA and field studies in British Columbia, Canada have shown that its lifecycle is highly synchronous with HWA phenology. This predator is being further evaluated for its suitability as a biological control agent. In order to be a viable candidate, L. nigrinus must survive under natural field conditions in the eastern United States, reduce the density of HWA, and it must be amenable to mass rearing. The survival, reproductive capability and predator efficiency of L. nigrinus were assessed over 3 years in the field. In addition, the environmental factors regulating processes in the life cycle to develop and improve rearing procedures for this insect were identified. In the first year, adults survived from February - May, laid up to 41 eggs/beetle, and consumed approximately 4.3 adelgids per day. In the second season, L. nigrinus adults survived from November - April, laid up to 38 eggs/beetle and consumed approximately 4.5 adelgids per beetle throughout the study. In both seasons, adelgid populations were significantly lower on branches with predators than those without predators. This impact was demonstrated on both the winter and spring generation of HWA. The feasibility of caged field releases of L. nigrinus was determined in a third field study. An estimated 10, 000 L. nigrinus eggs were liberated in field cages in spring 2003. The density of adelgids in the subsequent (spring) generation of the adelgids was significantly lower on branches with larval activity than those with no predators. Despite extensive sampling, no F1 adults were observed, however F2 adults were recovered in the fall of 2004, 20 months after release. The L. nigrinus life stages incurring high mortality during rearing were identified and factors affecting survival in the feeding and non-feeding life stages were investigated. Studies on the survival and feeding of adults, length of ovipositional period, density per cage, and survival of larvae were conducted. The effect of type of pupation medium, moisture level, disturbance, soil sterilization, temperature, and photoperiod on survival of the non-feeding stages and time of emergence from aestivation was examined. The most noteworthy finding, regarding rearing, is that aestivation can be extended by storing adults at high temperatures and long daylength throughout the summer and decreasing the temperature and daylength in the fall. Based on the results of these studies, procedures for rearing L. nigrinus have been developed and it is currently being reared at two other institutions. To date, over 8, 000 adults produced at Virginia Tech have been released in 6 states and both F1 and F2 adults have been recovered from multiple locations.

Browsing by Author "Kok, Loke T."

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