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.

Potential Risks of Poaceous Plants as Infectious Sources of Rice Black-Streaked Dwarf Virus Transmitted by the Small Brown Planthopper, Laodelphax striatellus.

The recent reemergence of rice black-streaked dwarf virus (RBSDV) has caused severe rice yield losses in several areas of East Asia. To identify the most important infectious sources of RBSDV, we compared the susceptibility of major poaceous plants to RBSDV infection and survival and the RBSDV acquisition efficiency of a vector insect, the small brown planthopper Laodelphax striatellus. RBSDV infection and survival rates of L. striatellus were significantly high in wheat (Triticum aestivum 'Norin61') and rice (Oryza sativa 'Reiho'), indicating that these crops can be important sources of RBSDV. Our results also showed that RBSDV can complete its infection cycle between Italian ryegrass (Lolium multiflorum 'Hataaoba') and L. striatellus. These results indicate that control of RBSDV and L. striatellus on winter-spring crops of wheat and Italian ryegrass may avoid an RBSDV epidemic on rice during the following summer. In addition to infections of wheat and Italian ryegrass, RBSDV infections were detected in Avena fatua, Avena sterilis subsp. ludoviciana, Cynosurus echinatus, Festuca arundinacea, Festuca pratensis, Lolium perenne, and Vulpia myuros var. megalura, although the infection efficiency varied.

Selection for imidacloprid resistance and mode of inheritance in the brown planthopper, Nilaparvata lugens.

BACKGROUND: Strong resistance to imidacloprid in Nilaparvata lugens (Stål) has developed in Southeast and East Asia. Although the mode of inheritance for resistance is very useful information for pest control, this information is unknown in N. lugens. Here, we established two resistant strains that were selected from field populations in Vietnam and the Philippines, and conducted crossing experiments to determine the inheritance pattern. RESULTS: The resistance ratio of 50% lethal dose (LD50 ) values for the two resistance-selected strains, i.e., resistant strains originating from Vietnam (VT-Res) and the Philippines (PH-Res), to their control strains were ∼ 8- and 157-fold, respectively. Reciprocal cross experiments between VT-Res and the susceptible strain (S-strain), and between PH-Res and the S-strain showed that the degree of dominance was 0.81 and 0.82, and 0.95 and 0.96, respectively. Analysis of the F2 populations and backcrosses to the parental strains indicated that resistance is a major-gene trait following Mendelian inheritance. The strength of the resistance was suppressed by pre-treatment with piperonyl butoxide, an inhibitor of cytochrome P450-monooxygenases. CONCLUSION: Our results suggest that imidacloprid resistance in N. lugens is autosomal and an almost completely dominant major-gene trait that is likely manifested by high expression levels of a detoxification enzyme. © 2019 Society of Chemical Industry.

Descriptions of two new species of Platygaster Latreille that attack gall midges (Diptera, Cecidomyiidae) with notes on their biology (Hymenoptera, Platygastridae).

Platygaster ingeniosus Matsuo & Yamagishi, sp. n. and P. urniphila Matsuo & Yamagishi, sp. n. (Hymenoptera: Platygastridae) are described from Japan. The former species is an egg-larval solitary parasitoid of Masakimyia pustulae Yukawa and Sunose (Diptera: Cecidomyiidae). The latter species is an egg-larval gregarious parasitoid of Rhopalomyia longitubifex (Shinji) (Diptera: Cecidomyiidae).

An endoparasitoid avoids hyperparasitism by manipulating immobile host herbivore to modify host plant morphology.

Many parasitic organisms have an ability to manipulate their hosts to increase their own fitness. In parasitoids, behavioral changes of mobile hosts to avoid or protect against predation and hyperparasitism have been intensively studied, but host manipulation by parasitoids associated with endophytic or immobile hosts has seldom been investigated. We examined the interactions between a gall inducer Masakimyia pustulae (Diptera: Cecidomyiidae) and its parasitoids. This gall midge induces dimorphic leaf galls, thick and thin types, on Euonymus japonicus (Celastraceae). Platygaster sp. was the most common primary parasitoid of M. pustulae. In galls attacked by Platygaster sp., whole gall thickness as well as thicknesses of upper and lower gall wall was significantly larger than unparasitized galls, regardless of the gall types, in many localities. In addition, localities and tree individuals significantly affected the thickness of gall. Galls attacked by Platygaster sp. were seldom hyperparasitized in the two gall types. These results strongly suggest that Platygaster sp. manipulates the host plant's development to avoid hyperparasitism by thickening galls.