Browsing by Author "Lim, Grace T."

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    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 (à ) using the formula = π;r²⁺; à , where r = ½ 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.
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    Host plants and associated trophobionts of the weaver ants Oecophylla spp. (Hymenoptera: Formicidae)
    Lim, Grace T.; Kirton, Laurence G.; Salom, Scott M.; Kok, Loke T.; Fell, Richard D.; Pfeiffer, Douglas G. (2008)
    Weaver ants (Oecophylla spp.) are often found on plants with insect symbionts (trophobionts), but the extent of such associations is not known. Examination of literature records of weaver ant host plants from 1900 to 2006 revealed that Oecophylla smaragdina, native to Asia, was recorded on 175 plant species in 46 families, with 28 associated trophobiont species in 7 families. Oecophylla longinoda, native to Africa, was recorded on 66 plant species in 34 families with 17 associated trophobiont species in 6 families. Both Oecophylla spp. shared host records on 17 economically important plant species. Such host plants could be used to augment establishment of weaver ants, facilitating their role as deterrents of phytophagous insect pests of economically important plants. O. smaragdina-tended trophobionts were recorded associating with the ants on several crops but rarely considered to be pests. Thus, the risk of trophobionts associated with Oecophylla ants being pests is considered minimal.