Abstract
Tephritid fruit flies are economically important orchard pests globally. While much effort has focused on controlling individual species with a combination of pesticides and biological control, less attention has been paid to managing assemblages of species. Although several tephritid species may co-occur in orchards/cultivated areas, especially in mixed-cropping schemes, their responses to pesticides may be highly variable. Furthermore, predictive efforts about toxicant effects are generally based on acute toxicity, with little or no regard to long-term population effects. Using a simple matrix model parameterized with life history data, we quantified the responses of several tephritid species to the sublethal effects of a toxicant acting on fecundity. Using a critical threshold to determine levels of fecundity reduction below which species are driven to local extinction, we determined that threshold levels vary widely for the three tephritid species. In particular, Bactrocera dorsalis was the most robust of the three species, followed by Ceratitis capitata, and then B. cucurbitae, suggesting individual species responses should be taken into account when planning for area-wide pest control. The rank-order of susceptibility contrasts with results from several field/lab studies testing the same species, suggesting that considering a combination of life history traits and individual species susceptibility is necessary for understanding population responses of species assemblages to toxicant exposure.
Highlights
Understanding how exposure to chemical compounds affects the population dynamics of economically important pest species is critical in developing effective integrated pest management schemes
Illustrates that in general we anticipate thetoxicological effects thatinsults sublethal. This illustratesThis that in general we cannot anticipate thecannot effects that sublethal may toxicological insults may have on one species based on the results of another—even when those species are members of the same family. This has extensive implications for the application of pesticides in polycultures that may harbor a suite of pest species, and is pertinent to the inclusion of pesticide sprays in IPM for area-wide control of orchard pests [19,20]
A surrogate species approach to pest management requires more attention to detail—including comparisons of specific vital rates derived from life table experiments among similar species
Summary
Understanding how exposure to chemical compounds affects the population dynamics of economically important pest species is critical in developing effective integrated pest management schemes. The methodologies used in pesticide risk assessment have lagged behind, with many such assessments relying heavily on static measures such as the LD50 /LC50. These measures are useful in ranking the toxicity of a wide range of toxicants, and, together with measures of exposure, can provide a framework for understanding potential effects on target and non-target organisms. By their very definition static metrics cannot capture longer-term population outcomes— those stemming from susceptibility
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