Location: Insect Behavior and Biocontrol ResearchTitle: Insecticide-mediated apparent displacement between two invasive species of Leafminer fly) Author
Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2012
Publication Date: 5/25/2012
Citation: Gao, Y., Reitz, S.R., Wei, Q., Yu, W., Lei, Z. 2012. Insecticide-mediated apparent displacement between two invasive species of Leafminer fly. PLoS One. PLoS ONE 7(5): e36622. Interpretive Summary: Invasive leafmining flies in the genus Liriomyza are among the most destructive pests of vegetable and ornamental crops worldwide. In particular, Liriomyza sativae and Liriomyza trifolii have been introduced throughout the world, and can attack many of the same crops. However, where the two species have both been introduced, one will often, rapidly displace the other. Both species have been introduced into southern China, with L. trifolii apparently displaced L. sativae soon after the introduction of L. trifolii. Scientists with the Chinese Academy of Agricultural Sciences and the USDA-Agriculture Research Service,Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Florida, conducted a series of laboratory and field experiments to determine if differential susceptibilities to insecticides could explain the ability of L. trifolii to have displaced L. sativae on Hainan Island, China. In the absence of insecticide treatments, the two species reproduced at similar levels. However, L. trifolii populations from southern China were found to be much less susceptible to the two most frequently used insecticides for leafminer management than were populations of L. sativae. These results are similar to the situation reported in California where differential insecticide tolerances are thought to have led to the displacement of L. sativae by L. trifolii. These results will be useful in understanding the population dynamics of these invasive species and improving management plans for them.
Technical Abstract: Closely related invasive species may often displace one another, but it is often difficult to determine mechanisms because of the historical nature of these events. The leafmining flies Liriomyza sativae and Liriomyza trifolii have become serious invasive agricultural pests throughout the world. Where both species have invaded the same region, one predominates over the other. Although L. sativae invaded Hainan Island of China first, it recently has been displaced by the newly invasive L. trifolii. We hypothesized that differential susceptibilities to insecticides could be causing this demographic shift. Methodology/Principal Findings Avermectin and cyromazine are the most commonly used insecticides to manage leafminers, with laboratory bioassays demonstrating that L. trifolii is significantly less susceptible to these key insecticides than is L. sativae. In trials where similar numbers of larvae of both species infested plants, which subsequently were treated with the insecticides, the eclosing adults were predominately L. trifolii, yet similar numbers of adults of both species eclosed from control plants. The species composition was then surveyed in two regions where L. trifolii has just begun to invade and both species are still common. In field trials, both species occurred in similar proportions before insecticide treatments began. Following applications of avermectin and cyromazine, almost all eclosing adults were L. trifolii in those treatment plots. In control plots, similar numbers of adults of the two species eclosed, lending further credence to the hypothesis that differential insecticide susceptibilities could be driving the ongoing displacement of L. sativae by L. trifolii. Conclusions/Significance Our results show that differential insecticide susceptibility can lead to rapid shifts in the demographics of pest complexes. Thus, successful pest management requires the identification of pest species to understand the outcome of insecticide applications. These results further demonstrate the importance of considering anthropogenic factors in the outcome of interspecific interactions.