Energy Reserve Compensating for Trade-Off Between Metabolic Resistance and Life History Traits in the Brown Planthopper (Hemiptera: Delphacidae).

Development of insecticide resistance often changes life history traits of insect pests, because metabolic detoxification of insecticides in insect bodies requires huge energetic reserves. The brown planthopper, Nilaparvata lugens (Stål), an important insect pest of rice crop in East and Southeast Asia, has developed strong resistance to imidacloprid from mid-2000s. The aim of this study was to examine the costs of life history traits and reveal changes in energy reserves with developing imidacloprid resistance. We compared the life history traits (survival time, fecundity, developmental time, and hatchability) and total lipid content between imidacloprid-resistant and imidacloprid-susceptible (control) brown planthopper strains. As compared to the control strains, adults' survival time of the resistant females was shorter, and their fecundity was lower; the other life history traits did not differ significantly between the resistant and control strains. As the results, net reproductive rates (R0) were lower in the resistant strains than in the susceptible strains. However, the amount of stored lipids was larger in resistant females than control ones. Our findings demonstrated a physiological trade-off between the development of imidacloprid resistance and the reproductive traits of brown planthopper. The imidacloprid-resistant strains are likely to store lipids for metabolic detoxification rather than consume them for reproduction.

Long-term field insecticide susceptibility data and laboratory experiments reveal evidence for cross resistance to other neonicotinoids in the imidacloprid-resistant brown planthopper Nilaparvata lugens.

BACKGROUND: Long-term monitoring data is helpful to understand the fluctuation of susceptibility and pattern of cross resistance in insecticide resistance management. After the occurrence of imidacloprid resistance, the brown planthopper (BPH) has gradually developed resistance to thiamethoxam and clothianidin since 2010, but not to dinotefuran and nitenpyram. Here, we analyzed susceptibilities data of five neonicotinoids during 2005-2017 in East Asia and Vietnam to conduct cross-resistance patterns among neonicotinoids. To determine the factors of development of cross resistance in laboratory bioassays, we used the imidacloprid resistant and control strains that were selected from filed populations in the Philippines and Vietnam. RESULTS: The Linear Mixed Models (LMM) analyses of insecticide susceptibility data showed that the slope values of imidacloprid resistance effects were 0.68 and 1.09 for resistance to thiamethoxam and clothianidin, respectively. Laboratory bioassay results showed that the LD50 values for thiamethoxam and clothianidin in resistant strains (1.4-5.5 µg g-1 ) were 3.2-16.4 times higher than those in the control strains (0.28-1.5 µg g-1 ). However, the increase in the LD50 values for imidacloprid was not related to that for dinotefuran and nitenpyram based on the results of the LMM analysis and laboratory bioassay. CONCLUSION: Our results demonstrate that the development of imidacloprid resistance result in strong-cross resistance to some neonicotinoids, thiamethoxam and clothianidin, but not to others, dinotefuran and nitenpyram. We anticipate that our findings will be a starting point for understanding mechanism of the different trend of cross resistance by analyzing long-term susceptibility data and laboratory bioassays in insect pests. © 2019 Society of Chemical Industry.

Insecticide susceptibilities of the two rice planthoppers Nilaparvata lugens and Sogatella furcifera in East Asia, the Red River Delta, and the Mekong Delta.

BACKGROUND: The two rice planthoppers, Nilaparvata lugens and Sogatella furcifera, have different life cycles in the regions of East Asia, the Red River Delta, and the Mekong Delta. The susceptibilities of these species to a range of insecticides have not previously been compared among the three regions over multiple years. Here, we describe the differences and similarities in insecticide susceptibilities of the two species among the three regions in 2006-2011. RESULTS: In all three regions in 2006 - 2011, N. lugens developed high and moderate levels of resistance to imidacloprid and thiamethoxam, respectively, but this species did not develop resistance to fipronil. In contrast, S. furcifera developed a high level of resistance to fipronil. The ranges in 50% lethal dose (LD50 ) values for N. lugens treated with both imidacloprid and thiamethoxam were similar over time between East Asia and the Red River Delta, and were different in the Mekong Delta. CONCLUSION: The results support the idea that resistant populations migrate from the Red River Delta region to East Asia. Therefore, continuous monitoring of the susceptibility of N. lugens to insecticides in the Red River Delta is very important for insecticide resistance management in East Asia. © 2017 Society of Chemical Industry.