Driving pest populations: Agricultural chemicals lead to an adaptive syndrome in Nilaparvata lugens Stal (Hemiptera: Delphacidae)

Authors: YOU, LIN-LIN - Yangzhou University; WU, YOU - Yangzhou University; XU, BING - Yangzhou University; DING, JUN - Yangzhou University; GE, LIN-QUAN - Yangzhou University; YANG, GUO-QIN - Yangzhou University; SONG, QI-SHENG - Yangzhou University; Stanley, David; WU, JIN-CAI - Yangzhou University

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2016
Publication Date: 11/23/2016
Citation: You, L., Wu, Y., Xu, B., Ding, J., Ge, L., Yang, G., Song, Q., Stanley, D.W., Wu, J. 2016. Driving pest populations: Agricultural chemicals lead to an adaptive syndrome in Nilaparvata lugens Stal (Hemiptera: Delphacidae). Scientific Reports. doi:10.1038/srep37430.

Interpretive Summary: Climate change will have marked effects on the activities of insect pests. Most attention has focused on their geographical ranges. A central problem, however, is the potential risks of exposing pest populations to low, non-lethal, levels of pesticides. The risks include increased numbers of generations per year, longer daily and annual activity periods and increased geographical ranges. These changes in pest populations may have severe consequences, including increased crop losses and decreased food security at the global level. In this paper we investigated the influence of the fungicide, jinggangmycin (JGM), used for decades to control rice blight on the brown planthopper (BPH), a pest of rice crops in temperate and tropical regions of Asia. BPHs are often present in rice crops at very high temperatures, close to BPH temperature survival limits. We tested whether JGM, a fungicide used to control rice blight in Asian rice production, increased the temperature survival limits of BPHs. JGM exposure significantly decreased mortality and increased survival at high temperatures. We investigated the underlying molecular mechanism. We discovered two proteins that are essential for surviving heat stress. We propose JGM induces survival in BPHs by increasing expression of proteins that act in cell protection mechanisms. These findings suggest that pest management programs can be improved by research to better understand stress tolerance induced by extrinsic factors. Scientists who study the influence of global climate change on pest insects will use the information in their research programs. Ultimately, this research will benefit growers who produce crops in high-temperature environments and the people who consume these crops.

Technical Abstract: Some of the effects of contemporary climate change and agricultural practices include increased pest ranges and thermotolerances and phonological mismatches between pest insects and their natural enemies. The brown planthopper (BPH) Nilaparvata lugens Stål (Hemiptera: Delphacidae) is a serious pest of rice crops. BPH outbreaks are associated with excess pesticide use and increasing global temperatures. We tested the hypothesis that JGM (a fungicide used to control rice blight) also enhances BPH thermotolerance. JGM exposure (200 ppm at 40 oC) led to decreased mortality (85% to 55%) and increased lethal mean time (LT50) of adults by 50%. The number of eggs laid by JGM-treated females at 26 oC (suitable temperature) and 34 oC (high temperature) increased by 44% and 49%, compared to controls. We selected Hsp70 and acetyl-CoA carboxylase (Acc) for detailed study. Transcripts encoding both proteins in 3rd instar nymphs and brachypterous adult females were up-regulated, compared to controls, after exposure to JGM. Suppressing Hsp70, but not Acc, led to 38% reduction in thermotolerance, from which we infer that JGM induced thermotolerance via Hsp70, not Acc. Suppressing Acc expression led to reduced egg laying (by 70%) at 34 oC and 26 oC. The influence of suppressing Hsp70 expression on fecundity was temperature-dependent because it led to a 74% reduction in egg laying at 34 oC, but not 26 oC. We infer that these two genes influence fecundity via different mechanisms, Acc through its actions in lipid biosynthesis and Hsp70 via its expected functions in cell protection. We suggest that the long-term efficacy of pest management programs requires a much more detailed understanding of pest insect adaptations to stressors, including increasing temperatures and agricultural chemicals.