Relative susceptibility to pesticides and environmental conditions of Frankliniella intonsa and F. occidentalis (Thysanoptera: Thripidae), an underlying reason for their asymmetrical occurrence

Abstract

To explain the asymmetrical abundance of native Frankliniella intonsa (Trybom) (Thysanoptera: Thripidae) and invasive Frankliniella occidentalis (Pergande) in the fields, we examined differential susceptibility to pesticides and environmental conditions, i.e., nine combinations of temperatures and relative humidities (RHs). We found adult female F . intonsa to be more susceptible to most of the tested insecticides as compared to F . occidentalis . Chlorfenapyr was most toxic to both thrips’ species. In the evaluation of environment conditions in the adult stage, F . intonsa survived 2.5 and 2.4-fold longer as RH increased at 20 and 25 °C, respectively, whereas F . occidentalis survived 1.8 and 1.6-fold longer, respectively. In both pupal and larval stage, no significant effect of interaction of temperatures and RHs was found between the two species. In conclusion, the insecticides tested differed considerably in their species-specific toxicity, and F . intonsa was generally more susceptible to the insecticides, while at the same time survivorship was better at higher RH conditions than F . occidentalis . Thus, differences in the relative susceptibility to changing environmental conditions, especially humidity, may be an underlying mechanism for the recent dominance of F . intonsa over F . occidentalis in the strawberry plastic greenhouse in Korea.

Spinetoram resistance drives interspecific competition between Megalurothrips usitatus and Frankliniella intonsa

“…2(B), (D)). In agreement with previous studies reporting on other thrips species replaced by F. occidentalis, 21,34 we can conclude that insecticide-mediated interspecific competition among thrips appears to be a key mechanism of displacements. Although the two native thrips reported here suggests that not all displacements involve invasive species, caution needs to be paid to their spread to other regions given their potential as invasive pests.…”

“…Together, these results demonstrate that F. intonsa is more dominant in abundance over M. usitatus under insecticide‐free situations, owing to the fast population increase of F. intonsa compared to M. usitatus . This similar result was also observed in interspecific competition between F. occidentalis and T. tabaci 35 or F. intonsa 21,34 in the treatments not exposed to insecticides. In contrast to non‐exposure tests, we surprisingly found that continuous exposure to spinetoram contributed to displacement of F. intonsa by M. usitatus (Fig.…”

“…Species displacement by the outcome of interspecific competition is of particular importance to pest management 21 . Together our results reported here may predict that F. intonsa will be replaced by M. usitatus in fields where spinetoram is frequently used.…”

“…Nevertheless, research to document the competitive interaction of thrips pests have focused on the most famous thrips Frankliniella occidentalis competing with several natives, 16 showing that their interplay is mainly mediated by competition asymmetry, 17 host plant, 18 female fecundity 19 and other abiotic factors 16 . Among the indistinguishable species belonging to thrips, Megalurothrips usitatu s (Bagnall) and Frankliniella intonsa (Trybom), two of the most common flower‐dwelling thrips, currently have caused huge damage to a wide range of leguminous crops throughout the world 20,21 . As two closely related thrips, M. usitatus and F. intonsa share a number of similarities, including biological traits, occurrence pattern and behavior habits 22,23 .…”

“…16 Among the indistinguishable species belonging to thrips, Megalurothrips usitatus (Bagnall) and Frankliniella intonsa (Trybom), two of the most common flower-dwelling thrips, currently have caused huge damage to a wide range of leguminous crops throughout the world. 20,21 As two closely related thrips, M. usitatus and F. intonsa share a number of similarities, including biological traits, occurrence pattern and behavior habits. 22,23 The two devastating thrips have posed an increasing threat to the cowpea industry in China, 23,24 leading to large economic losses through yield reductions and management costs.…”