Browsing by Author "Fell, Richard"

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    Aggregation, courtship, and behavioral interactions in European earwigs, Forficula auricularia L. (Dermaptera: Forficulidae)
    Walker, Karen Ann (Virginia Tech, 1997)
    Due to its relatively cool, humid summers, southwestern Virginia provides an ideal climate for European earwigs, Forficula auricularia. In 1990 - 1992, nymphs were captured in wooden groove-board traps beginning in late May, adults were captured beginning in mid-June, and disappeared from sampling sites by September or October. Sex ratios were significantly female-biased most of the season, becoming more marked by the fall. The pest status of F. auncularia is exacerbated by its gregarious nature. Gas chromatography-mass spectroscopy and accompanying behavioral bioassays showed that aggregation occurred as a result of a pheromone located on the male cuticle, which is probably a minor component of the hydrocarbon profile. Approximately 88% of the detected volatiles on the cuticle were identified as a series of normal and branched alkanes. Fatty acids and hydrocarbons were also identified in nymphal and adult legs, but these extracts were not attractive. Frass, which also contained fatty acids and hydrocarbons, was attractive, but likely acquired its attractancy through the earwigs' proclivity for consuming carcasses and exuviae. The defensive quinones produced by F aunculana repel conspecifics. A study of the behavioral repertoire of F. aunculana showed that, contrary to previous reports, only nymphs are nocturnal. Many differences in behavior were due to gender, age, and partner age. (e.g., females spent more time feeding than did males, adults fed more when paired with nymphs than when paired with adults). Social behaviors (communal feeding, aggression, contact, and dorsal palpation) comprised <10% of the insect's behavioral repertoire. Since dorsal palpation, a previously undescribed behavior and a form of allogrooming, occurred more frequently during reproductive periods, it may have a sexual significance. Dorsal palpation also may augment the distribution of defensive quinones on the cuticle of F. auricularia. An analysis of nymphal group dynamics demonstrated that as group size increased, nymphs spent significantly less time feeding alone and grooming, but more time resting. Antennal contact rates between group members increased significantly with group size. Detailed observations of the courtship and mating of F. auricularia revealed a complex of sexual behaviors for both males and females. Receptive females were behaviorally active during courtship. The significance of the male cerci was demonstrated by their use in early courtship with displays, and later use as a tactile stimulus for the female; and study of males from which the cerci had been removed, which showed no mating by amputated males. Male forcep length was bimodally distributed and positively allometric, while female forcep length was normally distributed. Males with longer forceps did not have a mating advantage. Further research is needed to identify the chemical composition of the aggregation pheromone, and to quantify any advantages of body and forcep size on mating success.
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    Aspects of the biology, behavior, bionomics, and control of immature stages of the cat flea Ctenocephalides felis felis (Bouche) (Siphonaptera: Pulicidae) in the domiciliary environment
    Byron, David W. (Virginia Polytechnic Institute and State University, 1987)
    The larval stage of the cat flea, Ctenocephalides felis felis (Bouche), was found to exhibit behaviors that were conducive to its security in carpet. Larvae exhibited positive geotactic, and negative phototactic behaviors. This resulted in the larvae spending greater than 80% of their time at the base of the carpet pile. Cat flea larvae also exhibited a positive hydrotaxis, and appeared to exhibit undirected movements when foraging. Larva were observed to respond to disturbances by coiling their body longitudinally. Cat flea hatched and unhatched eggs, and larval exuviae were found to be dispersed in a contagious fashion within carpet. The spatial pattern of the immature stages and remains was influenced by the habits of the pet host within a given room. First-instar larvae do not move far, if at all, from the location of eclosion. The movement of the larval stage is influenced by biotic and abiotic factors in the environment. Areas of high pedestrian or pet traffic are not conducive to successful eclosion from the egg or for successful larval development. Various methods of control exist for controlling an indoor infestation including both non-chemical and chemical tactics. A method for the physical control of immature stages in carpet is vacuuming. A beater-bar vacuum removes about 50% of the eggs but less than 30% of the larvae from a carpet. Chemical control tactics indoors are normally conducted using a compressed-air sprayer. Pressure within the application system is critical for creating spray patterns which can be overlapped to allow even insecticide coverage of the substrate. A compressed-air application system is not capable of delivering pesticides in a manner that will completely penetrate the carpet substrate to reach the base of the carpet. No significant differences in carpet penetration were observed over a range of 20 to 70 psi. Regardless of pressure, more than 93% of the solution applied to carpet was deposited in the upper third (6 mm) of the carpet. Pet owners were surveyed about their knowledge and perceptions of household infestations of the cat flea, and also about financial expenditures and their willingness to pay for a flea-free environment. The importance and the pest status of flea infestations were determined to be based on physical, psychological, and economic impacts on homeowners. Respondents' perceptions of infestations on their pet were associated with infestation levels in the house. The respondents were willing to pay more for flea control in July, the onset of the flea season, than they were at the peak or decline of the season. They were also willing to pay more as their perception of the intensity of the problem on the pet or in the home increased. Household income was not shown to affect a respondent's actual financial expenditures or his willingness to pay for flea control on the pet or in the home.
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    Biosystematics of the family dactylopiidae (Homoptera: Coccinea) with emphasis on the life cycle of dactylopius coccus costa
    Pérez Guerra, Gema (Virginia Tech, 1991-02-00)
    The cochineal insects include nine species assigned to the genus Dactylopius Costa, 1835, the only genus in the family Dactylopiidae. The present research is a comprehensive review of all the species in the family Dactylopiidae, with special emphasis on the life cycle of the type species Dactylopius coccus Costa. The adult females of the nine species have been redescribed and illustrated in detail, with a discussion on their morphological affinities and relationships. Their hosts, natural enemies, distribution, etymology, and role as biological control agents are discussed. For several species many new distribution and host records are given. Also, new types have been designated for some of the species. These included designation of one neotype and three paratypes for Dactylopius coccus Costa, one neotype for D. tomentosus (Lamarck), and designation of eight new topotypes for D. opuntiae (Cockerell). Methods are given on collecting, preservation and slide mounting, also on measurements and on preparation of illustrations. Cuticular ultrastructure is shown in scanning electron micrographs. All developmental stages of the type species D. coccus are described. The life cycles under two temperatures and relative humidities, for both males and females are discussed. Aspects of reproduction in D. coccus, its dispersal methods, factors affecting development, and its economic importance are also included. A separate chapter deals with the host-plants of Dactylopiidae. This includes data on host plant suitability and host plant resistance. Three identification keys are presented: one to the suborders of Homoptera, the other to the superfamilies and families of Coccinea, and another one for the determination of the species of Dactylopius. The phylogenetic relationships of the family Dactylopiidae with respect to all the Coccinea families is discussed. A phylogenetic tree for the Dactylopius species is proposed.
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    Catabolic substrate utilization patterns: varying humidity and dietary regimens in the American cockroach Periplaneta americana (L.) (Dictyoptera: Blattidae)
    Sherertz, Peter Chamness (Virginia Polytechnic Institute and State University, 1986)
    Changes in metabolic substrate utilization patterns resulting from exposure to varying humidity and dietary regimens were examined in the adult, male American cockroach. A series of respirometric experiments were conducted to monitor changes in respiratory quotient (RQ), oxygen quotient (QO₂), food and water consumption and body weight. Also, a series of radiolabel experiments, utilizing injected ¹⁴C-glucose and ¹⁴C-palmitic acid, were conducted to determine radiolabel content (after exposure to varying humidity and dietary regimens) in whole body, feces, ¹⁴CO₂, hemolymph, fat body tissue and cuticle. The results of these two series of experiments were compared to determine the overall effects of humidity and diet on catabolic substrate utilization pattern changes in the American cockroach. In these experiments, variation in dietary regimens appeared to play a more significant role than humidity variations with respect to significant differences observed in insect RQ, QO₂, body weight and radiolabel incorporation in whole body, ¹⁴CO₂ , hemolymph, and fat body tissue. However, humidity significantly affected radiolabel incorporation in fat body tissue in the glucose experiments and ¹⁴CO₂ in the palmitic acid experiments. RQ and QO₂ data from the respirometric experiments and ¹⁴CO₂ data from the radiolabel experiments suggested that cockroaches deprived of food, but provided water to drink, change their metabolic substrate utilization pattern from initial catabolic substrates such as carbohydrates to lipid-based substrates. Also, cockroaches deprived of either water (FO) or food and water (OO) appeared to change metabolic substrate utilization patterns toward carbohydrates, but the final carbohydrate metabolic substrates are still unknown. Cockroaches provided water, but no food, showed a change from initial RQ values (low humidity OW = 0.92 and medium humidity OW = 0.86) to terminal RQ values (low humidity OW = 0.71 and medium humidity OW = 0.68) representative of lipid-based substrate metabolism. There was also an unexplained decrease in QO₂ (initial low humidity OW = 0.45 ul/mg/hr and terminal low humidity OW = 0.28 ul/mg/hr; initial medium humidity OW = 0.35 ul/mg/hr and terminal medium humidity OW = 0. 30 ul/mg/hr). Also, cockroaches deprived of water (FO) or food and water (OO) showed an overall experimental rise in RQ values (initial low humidity FO = 0.87; and terminal low humidity FO = 0.87; initial medium humidity FO = 0.82 and terminal medium humidity FO = 0.85: initial low humidity OO = 0.79 and terminal low humidity OO = 0.88; initial medium humidity OO = 0. 75 and terminal medium humidity OO = 0.87). In addition, these same insects showed an overall experimental increase in QO₂ (initial low humidity FO = 0. 34 ul/mg/hr and terminal low humidity FO = 0.43 ul/mg/hr; initial medium humidity FO = 0.45 ul/mg/hr and terminal medium humidity FO = 0.49 ul/mg/hr: initial low humidity OO = 0.37 ul/mg/hr and terminal low humidity OO = 0.53 ul/mg/hr; initial medium humidity OO = 0.32 ul/mg/hr and terminal medium humidity OO = 0.45 ul/mg/hr), and in the radiolabelled glucose study OO insects showed an almost complete cessation of ¹⁴CO₂ release at 2 days (d). Terminal body weights differed significantly among cockroaches provided with both food and water (controls = FW), only water (OW), only food (FO) and no food or water (OO). Insects deprived of either water (FO) or food and water (OO) had significantly lower terminal body weights than those insects provided either water or food and water. Whole body water content increased and dry weight decreased in insects provided only water to drink.
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    Comparative genomics of Lactobacillaceae from the gut of honey bees, Apis mellifera, from the Eastern United States
    Bradford, Emma L.; Wax, Noah; Bueren, Emma K.; Walke, Jenifer B.; Fell, Richard; Belden, Lisa K.; Haak, David C. (Oxford University Press, 2022-12-01)
    Lactobacillaceae are an important family of lactic acid bacteria that play key roles in the gut microbiome of many animal species. In the honey bee (Apis mellifera) gut microbiome, many species of Lactobacillaceae are found, and there is functionally important strain-level variation in the bacteria. In this study, we completed whole-genome sequencing of 3 unique Lactobacillaceae isolates collected from hives in Virginia, USA. Using 107 genomes of known bee-associated Lactobacillaceae and Limosilactobacillus reuteri as an outgroup, the phylogenetics of the 3 isolates was assessed, and these isolates were identified as novel strains of Apilactobacillus kunkeei, Lactobacillus kullabergensis, and Bombilactobacillus mellis. Genome rearrangements, conserved orthologous genes (COG) categories and potential prophage regions were identified across the 3 novel strains. The new A. kunkeei strain was enriched in genes related to replication, recombination and repair, the L. kullabergensis strain was enriched for carbohydrate transport, and the B. mellis strain was enriched in transcription or transcriptional regulation and in some genes with unknown functions. Prophage regions were identified in the A. kunkeei and L. kullabergensis isolates. These new bee-associated strains add to our growing knowledge of the honey bee gut microbiome, and to Lactobacillaceae genomics more broadly.
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    Investigations of the destructive behavior, and method for control of the lesser mealworm, Alphitobius diaperinus (Panzer), (Coleoptera: Tenebrionidae)
    Despins, Joseph L. (Virginia Polytechnic Institute and State University, 1986)
    The relationship between the types of construction of high rise caged layer houses and insulation damage produced by the lesser mealworm was examined. Polyurethane insulation which had heavy-weight paper glued to its surface and was installed with tape to seal off the seam between the insulation boards had no infestations. Structures with concrete block pit walls had lower insulation infestations than those houses with wooden walls forming the pits. Houses with a support structure set on top of the concrete block pit wall had lower infestations than houses built with the support structure set directly into the earth. The insulation installed nearest the pit was the most severely infested, and infestation intensity was inversely proportional to insulation height above the manure pit. Damage in extruded polystyrene insulation resulted in a substantial loss of volume of material in the corner areas of the insulation panels, and caused a significant reduction in insulating quality. Observations were made on the effect of manure moisture and poultry house construction materials on lesser mealworm dispersal behavior. Larvae and adults preferred manure habitats of 30 and 40% moisture, and dispersal from the manure significantly increased when manure moisture was increased to levels of 50 and 60%. Larvae climbed a significantly greater distance up a vertical wooden surface than up a vertical concrete block surface under field conditions. Results indicate that structures built with wood pit walls are predisposed to infestations, and that fluctuating manure moisture levels in these houses can indirectly contribute to accelerated infestation by driving the larvae from the manure pits into the insulation. Insecticide sprays, plastic films, paint barriers applied to the surface of extruded polystyrene, and different types of insulation were evaluated for lesser mealworm resistance. In a laboratory study, tetrachlorvinphos and pirimiphos-methyl sprayed on extruded polystyrene produced greater than 90% mortality in larval and adult populations up to 71 weeks postapplication. Larvae were unable to penetrate either chlorpyrifos-impregnated or non-insecticidal polyethylene films. Infestation intensity was inversely proportional to insulation cell size. Effective treatments identified under field conditions were permethrin and pirimiphos-methyl sprays, and two formulations of chlorpyrifos-impregnated latex paint. Insulation materials with a cell size of 1.5 mm were resistant to lesser mealworm field populations.
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    Penetration and permanence of an organophosphate and a pyrethroid in structural wood for insect control
    Powell, Peggy K. (Virginia Tech, 1990)
    Studies were conducted on the penetration and permanence of 1.0% chlorpyrifos [0,0-diethyl 0-(3,5,6-trichloro-2-pyridyl) phosphorothioate], formulated as Dursban® TC (Dow Chemical Co.), in pine (Pinus spp.), spruce (Picea spp.), and fir (Abies spp.). Results indicated the highest degree of penetration in southern yellow pine. Surface roughness and orientation had an effect upon chemical penetration. Longevity studies ranging over time periods from three to 52 months revealed rapid loss of chlorpyrifos from the surface of the wood but relatively stable below-surface concentrations. Similar studies with 0.5% permethrin [(3-phenoxypheny]) methyl] (+) - cis, trans-3-(2,2-dichloroethenyl)-2,2dimethylcyclopropane-carboxylate] applied to the same wood types revealed comparable penetration differentials between types of wood. Formulation differences had little significant effect on penetration. One-year longevity studies revealed surface losses less drastic than those reported for chlorpyrifos, as well as superior below-surface stability. Studies employing volumes five, 10, and 25 times less than that required to achieve a runoff application revealed significantly lower chlorpyrifos penetration with reduced volume. Some reduced volumes resulted in below-surface concentrations of chlorpyrifos higher than the LC₉₀ value for Hylotrupes bajulus (Coleoptera: Cerambycidae). Toxicity testing with chlorpyrifos on first-instar larvae of H. bajulus, the old house borer, revealed contact LC₅₀ and LC₉₀ values of 14 ppm and 78 ppm, respectively. Similar tests with permethrin indicated LC₅₀ and LC₉₀ values of 2 ppm and 8 ppm. Tests with first-instar larvae on wood treated with 1.0% chlorpyrifos and 0.5% permethrin resulted in 100% mortality on wood aged for nine months in the case of chlorpyrifos, and six months in the case of permethrin. Tests utilizing H. bajulus eggs placed on treated wood revealed ovicidal properties of permethrin and lack of ovicidal effect with chlorpyrifos. Accelerated ageing studies employing an environmental chamber (40°C, 70% RH) at a 1:6 ratio of accelerated to natural weathering indicated no significant difference in surface or below-surface concentrations of permethrin in wood aged artificially for one month and in wood aged naturally for six months. Similar results were obtained with chlorpyrifos-treated wood artificially aged for 10 months and aged naturally for 4-1/3 years. Mathematical models were developed to predict surface and one millimeter concentrations of chlorpyrifos and permethrin after five and 10 years.
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    Pollination ecology of the simultaneously flowering Impatiens capensis and I. pallida
    Randall, John L. (Virginia Polytechnic Institute and State University, 1988)
    In mixed stands of the annual Impatiens capensis and I. pallida, bumblebees visit I. pallida almost exclusively even when the nutritional reward of I. pallida is removed. This phenomenon contradicts certain models proposed for foraging behavior in simultaneously flowering species and those dealing with optimal foraging. Such foraging behavior could have potentially devastating effects on the nonpreferred species, especially if the plant is an annual. Both Impatiens species share the same primary pollinators when they grow allopatrically, but when they grow sympatrically I. pallida continues to attract bumblebees while I. capensis depends on hummingbirds and small bees for pollination. Thus competition for pollinators between these Impatiens represents an important plant-plant and plant·pollinator interaction with potential consequences. When I. capensis is less frequented by bumblebees when sympatric with I. pallida, I. capensis exhibits reduced fecundity. Mechanisms of interference through improper pollen transfer are described for the Impatiens species. Pollen of I. pallida adheres to and germinates on the stigmas of I. capensis and the pollen tubes reach the ovules. In contrast, pollen of I. capensis adheres poorly to I. pallida stigmas and fails to germinate. No hybridization occurs between the species. Scanning electron micrographs of pollen and stigma surfaces of the two species revealed no morphological differences. Among the floral characteristics examined, only flower color appeared to influence bumblebee preference for I. pallida. Differences between the species in ultraviolet absorbance patterns, perianth size and shape, odor, and nectar quantity and quality did not affect the pollinator preference of bumblebees. Differences in nectar characteristics and production rate were found among Impatiens populations. However, nectar quantity, quality, and production rates did not differ within allopatric or sympatric populations, but both species had higher nectar volumes with lower solute concentrations in the morning, and lower nectar volumes with higher solute concentrations in the late afternoon. Differences in nectar volumes among populations appeared to be associated with environmental factors affecting population sites. I. capensis avoids competition and maintains itself in sympatric populations with I. pallida by depending on hummingbirds and insects other than bumblebees as pollinators, and has the ability to produce cleistogamous flowers and their subsequent progeny to ensure sexual reproduction. However, inbred progeny of I. capensis are competitively inferior to outcrossed stock. Nevertheless, I. capensis does persist in mixed stands of I. pallida despite the absence of bumblebee pollination and the presence of lower seed set.
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    Quantification of tobacco aphid, Myzus nicotianae Blackman, injury to flue-cured tobacco, Nicotiana tabacum (L.)
    Reed, T. David (Virginia Tech, 1990)
    A two year study was conducted to measure the impact of tobacco aphid, Myzus nicotianae Blackman, colonization and cumulative aphid-days on flue-cured tobacco, Nicotiana tabacum (L.). The objectives of the study included quantifying the response of tobacco production variables, cured leaf quality, and cured leaf chemical analysis to the level of cumulative aphid-days. Aphid populations and tobacco plant responses were recorded on an individual plant basis. A gradient in cumulative aphid-days was obtained through the use of temporally distributed aphid colonizations and selective insecticide use. Tobacco aphid populations resulted in yield reductions as great as 22 and 27% in 1988 and 1989, respectively, while gross economic returns were reduced 27 and 32% in the respective years. The responses of tobacco production variables were characterized by a decreasing negative slope; therefore, incremental losses were greatest at low levels of cumulative aphid-days. Regression models were developed to describe crop production responses as a function of cumulative aphiddays. The quality of the cured leaves (grade index) was also responsive to the level of cumulative aphid-days. Changes in both tobacco grade group and quality within a given group occurred with increasing cumulative aphid-days. The occurrence of nondescript tobacco was associated with large aphid populations. The chemical quality of the cured tobacco was also influenced by cumulative aphid-days. The total alkaloid content followed a linear function, while the level of reducing sugars was a nonlinear relationship with cumulative aphid-days. The study also reported on the disproportionate impact of aphid populations upon the within-plant responses of tobacco. A study was conducted to evaluate the impact of tobacco aphid management using eight different action thresholds. Comparison of the two most commonly recommended treatment thresholds (10 and 20% of plants with 50 or more aphids per leaf) revealed no significant differences in the number of remedial treatments required or the yield and gross economic returns. However, use of the latter threshold resulted in a delay of approximately one week for the first treatment and the retreatment interval.
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    A study of factors affecting queen survival, nest initiation, and nest development in the baldfaced hornet Dolichovespula maculata (L.) (Hymenoptera:Vespidae)
    Stein, Kenneth John (Virginia Tech, 1990)
    Mating success and nutrient reserve effects on queen survival and nest initiation were examined with respect to the reproductive fitness of queens of the baldfaced hornet, Dolichovespula maculata. The sperm content of the Spermatheca was examined in queens of this hornet species and in queens of 10 other yellowjacket species collected in spring and summer of 1987, 1988 and 1989. Queens of the baldfaced hornet, D. maculata, were also analyzed for sperm content prior to nest initiation and during colony development. A regression model was employed to determine sperm utilization. Based on total cell counts and adult census, the sperm use efficiency of this species changed from approximately 90-100 sperm released per egg in the initial stages of colony development, to 2-3 sperm released per egg after 1000 eggs had been laid. Near the end of the season the predicted number of sperm released per egg was 0-1. The number of sperm in D. maculata males ranged from 2-2.5 million; a value considerably greater than the mean sperm number (20,223; ±4,669) found in mated spring queens (n=15). Nineteen (18.4%) of 103 yellowjacket queens analyzed in the spring seasons of 1987 and 1988 were uninseminated. The effects of mating success and sperm utilization on colony development are discussed. A significant regression of sperm content on colony size was also found for 8 species of yellowjacket. Queens of D. maculata were collected for studies of nutrient reserves before hibernation in the fall, during nest initiation, and after colonies had produced more than 2 worker broods. Fresh and dry weights were determined for all queens and a seasonal comparison of the energy reserves of lipids, sugar, and glycogen was performed on the thoracic and abdominal tagmata. Total nitrogen was also quantified to estimate protein changes by season. The results show that lipids accounted for 35% of the weight lost during hibernation, sugars 12%, and glycogen 6%. Total thoracic nitrogen remained constant throughout the year, whereas abdominal nitrogen was the same in the fall and spring queens but increased in the summer queens. The results from this study suggest that most queens which survive the winter and successfully initiate nests have similar energy reserve quantities. The implications of these findings to solitary foraging behavior are discussed. The eggs of D. maculata were examined in the spring and summer to quantify the energetic contributions provided by the queen. Mean egg weight was highest in the spring and decreased with progressive nest development. Both egg weight and energy reserves were variable among and within nests. The nutrient reserves for eggs in embryo nests, in order of importance, were lipid (22%), glucose (9.5%), and glycogen (5%). A 10-day egg incubation experiment demonstrated a mean loss of 83 ug dry weight; lipids could not completely account for the weight loss, either quantitatively or qualitatively. A study on egg developmental time failed to provide sufficient data; all eggs eventually died although embryonic larval movement was detected in 2 eggs after 16 days. The energetic contributions which a queen provides to the eggs are discussed with respect to foraging behavior and environmental influences.
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    Sublethal vapor-induced responses of the German cockroach to commercial pesticide formulations
    Wooster, Mark T. (Virginia Polytechnic Institute and State University, 1988)
    The overall purpose of this study was to examine the effects of an insecticide vapor pulse on the dispersal response of the German cockroach, Blattella germanica (L). An apparatus was designed to expose test cockroaches to vapors from commercial pesticide formulations. Insecticide vapor-induced dispersal responses were recorded during a two hour period from different strains that had been allowed to acclimate to a harborage. The dispersal response of large nymphs from a pesticide susceptible laboratory strain (VPI) was compared to two propoxur resistant field strains (Carver, Kenly) after exposure to four propoxur formulations and their blanks. Vapors from the petroleum-based oil and aerosol formulations induced significantly more dispersal than vapors from water-based emulsifiable concentrate and wettable powder formulations. Vapors from formulations containing the toxicant generally induced a significantly faster dispersal response than did their blanks. Exposure of cockroaches to the vapors of diazinon, malathion, and cyfluthrin indicated that the class of pesticide can also influence the dispersal response. Strain differences were found in experiments with the propoxur formulations, their blanks, malathion, and cyfluthrin. Slow dispersal precluded demonstration of significant strain differences in experiments with diazinon. Exposure of mixed age groups of four strains to vapors from 1% propoxur-in-oil, an aerosol and their blanks indicated that dispersal patterns were similar to the single age class experiments. Inter- and intra-strain differences were found. Dispersal of the field strains was distinguished from that of the laboratory strain by more variable responses and differences among age classes. The strongest inter-and intra-strain differences were in response to the solvents rather than the complete formulation. The air concentration of propoxur from a 1% oil formulation was estimated at 146 pg/ml. Condensation of the toxicant onto the apparatus was also observed. Vapor pulse characteristics for the four propoxur formulations indicated that the equilibrium vaporization rate in the test apparatus was approximately 0.5 mg/min for the oil and aerosol formulations and 1.0 mg/min for the WP and EC formulations. Results suggest that effective control strategies must be tailored for each target population.