Whole genome sequencing of spotted stem borer, Chilo partellus, reveals multiple genes encoding enzymes for detoxification of insecticides.

Spotted stem borer, Chilo partellus, is the most important constraint for increasing the production and productivity of maize and sorghum, the two major coarse cereals in Asia and Africa. The levels of resistance to this pest in the cultivated germplasm are low to moderate, and hence, farmers have to use insecticides for effective control of this pest. However, there is no information on the detoxification mechanisms in C. partellus, which is one of the constraints for deployment of appropriate insecticides to control this pest. The ability to detoxify insecticides varies across insect populations, and hence, we sequenced different populations of C. partellus to identify and understand detoxification mechanisms to devise appropriate strategies for deployment of different insecticides for controlling this pest. Larval samples were sequenced from three different cohorts of C. partellus using the Illumina HiSeq 2500 platform. The data were subjected to identify putative genes that are involved in detoxification on insecticides in our cohort insect species. These studies resulted in identification of 64 cytochrome P450 genes (CYP450s), and 36 glutathione S-transferases genes (GSTs) encoding metabolic detoxification enzymes, primarily responsible for xenobiotic metabolism in insects. A total of 183 circadian genes with > 80% homolog and 11 olfactory receptor genes that mediate chemical cues were found in the C. partellus genome. Also, target receptors related to insecticide action, 4 acetylcholinesterase (AChE), 14 γ-aminobutyric acid (GABA), and 15 nicotinic acetylcholine (nAChR) receptors were detected. This is the first report of whole genome sequencing of C. partellus useful for understanding mode of action of different insecticides, and mechanisms of detoxification and designing target-specific insecticides to develop appropriate strategies to control C. partellus for sustainable crop production.

Ecotoxicity of neonicotinoids and diamides on population growth performance of Zygogramma bicolorata (Coleoptera: Chrysomelidae).

Relative ecotoxicity of approved neonicotinoids (i.e. imidacloprid, clothianidin, acetamiprid, thiacloprid, thiamethoxam and dinotefuran) and diamides (i.e. chlorantraniliprole, cyantraniliprole and flubendiamide) was examined on population growth parameters of Zygogramma bicolorata Pallister on parthenium under laboratory conditions at 27 ± 1 °C, 65 ± 5% relative humidity and 10 L : 14D photoperiod. The dose of all tested insecticides in the bioassay procedure was within a minimum range of their recommended field rate. In acute toxicity trial, imidacloprid caused highest rate of mortality in treated adults of Z. bicolorata, however, it was lowest in flubendiamide treatment followed by cyantraniliprole and chlorantraniliprole. Further, based on toxicity coefficient (E) value in acute toxicity trial, all were classified as harmful (H) and diamides were classified as moderately harmful (MH) as per IOBC classification. Moreover, chronic toxicity trials were carried out through life table response experiments (LTREs) in the F1 progeny of acute toxicity experienced group. Prolonged development with the highest mortality was evident in as compared to diamides. Furthermore, population growth parameters i.e. potential fecundity (Pf), natality rate (mx), intrinsic rate of increase (rm), net reproductive rate (R0) and finite rate of increase (λ) was greatly reduced in Z. bicolorata treated with neonicotinoids as compared with diamides. However, mean generation time (Tc), corrected generation time (τ) and the doubling time (DT) was prolonged in neonicotinoids followed by diamides. Furthermore, proportion of females was greatly reduced (0.43-0.48 females) in neonicotinoids as comparison to diamides (0.53-0.55 females) and control (0.67 females). On the basis of ecotoxicity trials, the tested neonicotinoids were highly toxic to Z. bicolorata than diamides. Therefore, diamide insecticides could be used with Z. bicolorata, however, for validation experimentation need to be done under natural field conditions.

Non-target toxicity of synthetic insecticides on the biological performance and population growth of Bracon hebetor Say.

Bracon hebetor Say (Hymenoptera: Braconidae) is an important biological control agent of various species of order Lepidoptera and extensively used in biological control program worldwide. Present study evaluated the lethal and sublethal effects of insecticides on B. hebetor using demographic and population growth parameters. Doses of all the tested insecticides were within a maximum range of their recommended field dosages and adults were treated using residual glass vials method. For control experiments adults were treated with distilled water. Among the tested insecticides, the survivorship of various stages of B. hebetor was considerably prolonged on cyantraniliprole followed by chlorantraniliprole and shortest on chlorpyrifos and profenofos treated group. Total immature development time was prolonged in chlorpyrifos and profenofos treated group. Population growth parameters like intrinsic rate of natural increase (rm), net reproductive rate (R0), finite rate of increase (λ) and mean generation time (Tc) were considerably reduced in B. hebetor groups treated with chlorpyrifos and profenofos. However, B. hebetor groups treated with chlorantraniliprole and cyantraniliprole showed a little or no much difference in population growth parameters when compared with untreated group. It was also observed that chlorpyrifos and profenofos modified the sex ratio, thereby female emergence get reduced. On the basis of present findings it can be concluded that all tested insecticides caused considerable ecotoxic effects on B. hebetor compared to control. However, comparisons among the tested insecticides on the basis of IOBC criteria showed that chlorantraniliprol and cyntraniliprol was less toxic as compared to other insecticides tested on this biological control agent.

Temperature-dependent development of diapausing larvae of Chilo partellus (Swinhoe) (Lepidoptera: Crambidae).

Temperature-dependent development rate, percent diapause induction (hibernation at low temperature and aestivation at high temperature), and survival of diapausing larvae of Chilo partellus (Swinhoe, 1885) were examined on 13 constant temperatures ranging from 8 to 40°C. Development of hibernating and aestivating larvae occurred from 10 to 25°C and 27-38°C, respectively. However, no development occurred at 8°C and 40°C. To determine actual thermal conditions that affect development and trigger both kind of diapause (hibernation and aestivation), various thermal parameters were estimated by fitting the development rate data to two linear (Ordinary equation and Ikemoto & Takai) models and thirteen non-linear models. The lower thermal thresholds (Tmin) for development of diapausing larvae of C. partellus were calculated as 9.60°C and 10.29°C using the ordinary linear model and Ikemoto & Takai model, respectively. Similarly, the thermal constants (K) estimated using the ordinary linear model was 333.33 degree-days and that estimated with Ikemoto & Takai model was 338.92 degree-days. Among the non-linear models, Lactin-2 followed by Lactin-1 were found to be the best as these models estimated the critical temperatures (Tmin, Tmax and Topt) similar to those of observed values. Conclusively, the Ikemoto & Takai linear model and Lactin-2 followed by Lactin-1 non-linear models are useful and efficient for describing temperature-dependent development and estimating the temperature thresholds of diapausing larvae of C. partellus. Our findings provided fundamental information for estimation of thermal requirement and temperature based development models for diapausing larvae of C. partellus. This information will be highly useful for predicting the occurrence, seasonal emergence, number of generations and population dynamics of C. partellus.

Lipid composition differs in diapause and nondiapause states of spotted stem borer, Chilo partellus.

Spotted stem borer, Chilo partellus, undergoes larval diapause (hibernation and aestivation), and depends on the food reserve accumulated during feeding stage for its survival. Lipids are the primary source of energy during diapause, and essential for different cellular, biochemical and physiological functions. However, there is no information on lipid and lipophilic compound contents during different stages of hibernation, aestivation and nondiapause in C. partellus. Thus, we compared the concentration and composition of lipids in pre-diapause, diapause and post-diapause stages of hibernation and aestivation with nondiapause stages of C. partellus. The studies revealed significant differences in total lipids and various lipophilic compounds during different stages of diapause as compared to nondiapause C. partellus. The total lipids were significantly lower during diapause stage of aestivation and hibernation as compared to nondiapause larvae. Further, the linoleic acid, Methyl 3-methoxytetradecanoate, and l-(+)-Ascorbic acid 2,6-dihexadecanoate were significantly lower, and oleic and palmitoleic acids greater during pre-diapause and diapause stages of hibernation and aestivation as compared to nondiapause larvae. The cholesterol content was significantly greater during pre-diapause stage of hibernation, and diapause and post-diapause stages of aestivation as compared to nondiapause stages. The unsaturation ratio was significantly higher in the pre-diapause and diapause stages and lower in post-diapause stage of aestivation than the hibernation and nondiapause states. This study provides insights on differential lipid profiles during different phases of diapause, which could be useful for further understanding biochemical and physiological cross-talk, and develop target-specific technologies for the management of C. partellus.

Biological and biochemical diversity in different biotypes of spotted stem borer, Chilo partellus (Swinhoe) in India.

Because of variation in incidence and severity of damage by Chilo partellus (Swinhoe) in different geographical regions, it is difficult to identify stable sources of resistance against this pest. Therefore, the present studies were undertaken on biological attributes (damage in resistant and susceptible genotypes, survival and development) and biochemical profiles (amino acids and lipophilic compound) of C. partellus populations from eight geographical regions to understand it's population structure in India. There was a significant variation in biological attributes and biochemical profiles of C. partellus populations from different geographical regions. Based on virulence and biological attributes, similarity index placed the C. partellus populations in five groups. Likewise, lipophilic and amino acid profiling also placed the C. partellus populations in five groups. However, the different clusters based on biological and biochemical attributes did not include populations from the same regions. Similarity index based on virulence, biological attributes, and amino acids and lipophilic profiles placed the C. partellus populations in six groups. The C. partellus populations from Hisar, Hyderabad, Parbhani and Coimbatore were distinct from each other, indicating that there are four biotypes of C. partellus in India. The results suggested that sorghum and maize genotypes need to be tested against these four populations to identify stable sources of resistance. However, there is a need for further studies to establish the restriction in gene flow through molecular approaches across geographical regions to establish the distinctiveness of different biotypes of C. partellus in India.

Does Zygogramma bicolorata Pallister really affects the growth, density and reproductive performance of Parthenium hysterophorus L?

Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) is a satisfactory potential candidate for controlling Parthenium hysterophorus L. The study was conducted in order to evaluate the bio-control potential of Z. bicolorata to satisfactory reduced the density of parthenium weed in natural field conditions. Therefore, beetles were released in the twelve study sites @ 12 adults and/or larvae/m2 in their respective sites on 5th, 10th, 15th and 20th day after initial field releases. Observations were made on defoliation by the beetle, perthenium plant height, plant biomass, leaf injury rating and soil seed reservoir. Present study showed that field releases of Z. bicolorata considerably lowering down the parthenium density at all treated sites. At larval release sites by the 60th day of observation a complete defoliation was noted, however at adult release sites it took 80 days for complete defoliation. Moreover, significantly higher number of developmental stages i.e. eggs, larvae and adults were noted in the adults released sites than to larval released sites and the controls. It was also noted that plant height and its density, flowers & leaves production, biomass of parthenium plant and seed reservoir in soil was negatively affected in treated sites as compared to untreated sites. Thus, we have concluded that adults can be utilized in biocontrol program because population build-up was greater in those sites where adults were released.

Genetic regulation of diapause and associated traits in Chilo partellus (Swinhoe).

Diapause is an endocrine controlled arrested metabolic state to delay development or reproduction under unfavorable conditions. To gain an understanding of importance of diapause for ecological adaptation, it is important to study regulation of diapause in insects. We examined genetics of diapause in Chilo partellus by crossing the hibernating (HD), aestivating (AD), post-hibernating (PHD), post-aestivating (PAD), and nondiapause (ND) strains. Reciprocal crosses were also made to gain full understanding of diapause regulation and the maternal effects, if any. Data were recorded on fecundity, egg hatching, larval survival, diapause induction and termination, adult emergence, and morphometrics of larvae, pupae and adults in the parents (P1, P2), F1 hybrids, and the reciprocal crosses. Genetic analysis showed that AD strain is general combiner, which also improved egg hatching, larval survival, diapause termination, adult emergence and proportion of females in the progenies. Incidence of diapause was highest in HD × AD, whereas termination was greatest in PHD × AD. However, ND strain and its reciprocal crosses with other strains did not exhibit any noticeable developmental response associated with diapause. Specific combining ability analysis suggested that where PHD and AD strains exist together there will be likely reduction in diapause incidence, increased survival with greater fitness and faster multiplication of their progenies resulting in outbreak of C. partellus. Degree of dominance estimates revealed that diapause, developmental and morphometric traits in C. partellus are governed by over dominance gene effects, and mainly depend on parental diapause history.

Fitness consequences of delayed mating on reproductive performance of Chilo partellus (Swinhoe).

We investigated the effects of mating among different-aged males and females on reproductive physiology, progeny production, and longevity of Chilo partellus (Swinhoe) adults under laboratory conditions. Present studies involved virgin males (M) and females (F) of three different ages namely, on the day of emergence (1D), next day (2D), and further next day (3D), thus comprising of a total of nine mating treatments (1DM × 1DF, 1DM × 2DF, 1DM × 3DF, 2DM × 1DF, 2DM × 2DF, 2DM × 3DF, 3DM × 1DF, 3DM × 2DF, and 3DM × 3DF). The observations were recorded on fecundity, fertility, hatchability, and longevity of male and female adults. We found that mating among old aged males and females significantly reduce fecundity, fertility, and egg hatchability. Further, the fecundity, fertility, and egg hatching were significantly higher when newly emerged females mated with either of the ages of males as compared with other mating treatments. Conversely, the 3-day-old females, when mated with either of the ages of males, laid more numbers of unfertilized eggs, thus reduction in egg hatchability. Mating among newly emerged adults significantly reduced the longevity of male and female adults. Kaplan-Meier estimation showed that none of the adults across mating treatments survived more than 6 days. The recovery of spermatophores from the reproductive tract of females from 3DM × 1DF were significantly higher than other mating treatments. However, no association was found between spermatophore recovery and longevity of male and female adults. Findings of present studies will help to devise appropriate techniques to disrupt mating and suppress C. partellus population under field conditions.

Factors responsible for estivation in spotted stem borer, Chilo partellus (Swinhoe).

Diapause is an important adaptive trait in certain groups of insects at a particular stage, which contribute in controlling insect ecology, phenology, and physiology. Considering the importance of various factors in appropriate combinations, we studied effects of different temperature and photoperiod conditions on larval morphometrics, development, induction, and termination of estivation, and overall mortality due to estivation in Chilo partellus (Swinhoe). Weight, length, and head capsule width of C. partellus larvae significantly increased with increase in temperature and photoperiod treatments upto certain age and duration of exposure. According to Dyar's ratio, overall head capsule width progressed geometrically with minimum constant ratio of 1.20, and second-degree polynomial regression equations were best fitted to all the test treatment conditions. The mortality of diapausing C. partellus individuals varied between 7.0% and 37.3% under different constant and varying temperature and photoperiod regimes, which at 38°C + 14L:10D reached upto 100.0%. However, the exposure to 30°C + 12.5L:11.5D and 32°C + 13L:11D along with dry food accelerated the process of estivation, wherein the diapause larval survival was significantly higher and overall mortality of individuals due to diapause was lower suggesting these conditions appropriate for induction of estivation in C. partellus. These studies have implications for better understanding the bioecology and population regulation system under varying climatic conditions and devising novel strategies for management of C. partellus.

Ecotoxicological hazards of herbicides on biological attributes of Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae).

Ecotoxic effects of commonly used herbicides i.e. glyphosate, atrazine, metribuzin, alachlor and 2, 4-D were evaluated on the biological and demographic parameters of Zygogramma bicolorata Pallister on parthenium in laboratory. The herbicides used in the bioassay were within a minimum range of their recommended field dose. In direct toxicity experiment, 2,4-D and alachlor caused the highest mortality of 3rd instars and prolonged the development time. Fecundity and eggs viability were also significantly reduced in all treatments. Indirect toxicity (carryover effect) was evaluated through life table analysis of F1 progenies developed from surviving 3rd instars treated for direct toxicity experiment. Incubation period and overall development time was considerably prolonged in all treatments especially in 2, 4-D treated group. Daily fecundity and population growth parameters were significantly lowest in 2, 4-D treated groups compared to other tested herbicides. A significantly greater number of females were produced in glyphosate treatment than other treatments. Based on the present study, none of the tested herbicide can be classified as safe to Zygogramma bicolorata, while glyphosate was found to be least toxic. Therefore, it can be concluded that application of field recommended dose of glyphosate might be used in integration with Z. bicolorata for effective management of parthenium, however this needs to be conducted under natural field conditions.

Superparasitism in Cotesia glomerata does not benefit the host plant by reduction of herbivory caused by Pieris brassicae.

Superparasitism occurs in Cotesia glomerata L. (Hymenoptera: Braconidae), a gregarious endoparasitoid of Pieris spp. (Lepidoptera: Pieridae). The responses of Pieris brassicae L. larvae to superparasitism were examined in order to elucidate the ecological significance of this behaviour. Models of tritrophic interactions often imply that attraction of herbivore natural enemies by the plant constitutes a defence. Parasitoid attack on herbivores is assumed to result in a reduction in herbivory and or an increase in plant fitness. Coupled with the active involvement of the plant in producing signals, this can be seen as an indirect mediation of wound induced defence. The results show that superparasitism of P. brassicae by the parasitoid C. glomerata reduced survivorship but increased food consumption and weight growth in P. brassicae larvae. The duration of host larval development was found prolonged as the number of oviposition increased and superparasitized larvae (three to five time parasitized) grew slower than unparasitized larvae or larvae parasitized one or two times.