Spinetoram resistance drives interspecific competition between Megalurothrips usitatus and Frankliniella intonsa

Abstract

BACKGROUND: Species displacement by the outcome of interspecific competition is of particular importance to pest management. Over the past decade, spinetoram has been extensively applied in control of the two closely related thrips Megalurothrips usitatus and Frankliniella intonsa worldwide, while whether its resistance is implicated in mediating interspecific interplay of the two thrips remains elusive to date. RESULTS: Field population dynamics (from 2017 to 2019) demonstrated a trend toward displacement of F. intonsa by M. usitatus on cowpea crops, supporting an existing interspecific competition. Following exposure to spinetoram, M. usitatus became the predominate species, which suggests the use of spinetoram appears to be responsible for mediating interspecific interactions of the two thrips. Further annual and seasonal analysis (from 2016 to 2020) of field-evolved resistance dynamics revealed that M. usitatus developed remarkably higher resistance to spinetoram compared to that of F. intonsa, implying a close relationship between evolution of spinetoram resistance and their competitive interactions. After 12 generations of laboratory selection, resistance to spinetoram in M. usitatus and F. intonsa increased up to 64.50-fold and 28.33-fold, and the average realized heritability (h 2 ) of resistance was calculated as 0.2550 and 0.1602, respectively. Interestingly, two-sex life table analysis showed that the spinetoram-resistant strain of F. intonsa exhibited existing fitness costs, but not the M. usitatus. These indicate that a rapid development of spinetoram resistance and the lack of associated fitness costs may be the mechanism underlying recent dominance of M. usitatus over F. intonsa.CONCLUSION: Collectively, our results uncover the involvement of insecticide resistance in conferring displacement mechanism behind interspecific competition, providing a framework for understanding the significance of the evolutionary relationships among insects under ongoing changing environments. These findings also can be invaluable in proposing the most appropriate strategies for sustainable thrips control programs.

Variation in the toxicity of a novel meta‐diamide insecticide, broflanilide, among thrips pest species and developmental stages

“…Fitness costs can affect the incidence of resistance, but there are few resistance cases in thrips with fitness costs 38 . If there is a fitness cost in the resistant population of thrips to the broflanilide, restoration of susceptibility might be expected when there is no selection pressure.…”

“…Fitness costs can affect the incidence of resistance, but there are few resistance cases in thrips with fitness costs. 38 If there is a fitness cost in the resistant population of thrips to the broflanilide, restoration of susceptibility might be expected when there is no selection pressure. On the other hand, thrips are easily dispersed by human activities due to their small body size, 39,40 and human-mediated dispersal may accelerate the introduction of the resistant alleles across a wide range.…”

Interspecific and intraspecific variation in susceptibility of two co‐occurring pest thrips, Frankliniella occidentalis and Thrips palmi, to nine insecticides

“…In a previous comparison of toxicity to spinetoram involving T. palmi , F. occidentalis , and F. intonsa populations across China, T. palmi was considered the least susceptible species 15 . Fu et al 17 . noted differences in susceptibility to spinetoram between Megalurothrips usitatus and F. intonsa , while F. occidentalis was less susceptible than T. tabaci to avermectin and beta‐cypermethrin.…”

“…Species displacement is a common phenomenon among thrips 7 . The performance of thrips can be influenced by biotic and abiotic factors and thus mediate species competition 16,17,55,56 . Insecticides are a strong field driver of changes in the dominance of pest thrips species 16,17 .…”

“…Previous studies have focused on resistance in limited species, especially the invasive western flower thrips Frankliniella occidentalis 9,10,14 . With variation in the resistance of thrips to insecticides developing within and among species, 15 there is potential for chemical applications to result in field displacement of thrips species 16,17 …”