Antagonistic regulation, yet synergistic defense: effect of bergapten and protease inhibitor on development of cowpea bruchid Callosobruchus maculatus

Combining Experimental Evolution and Genomics to Understand How Seed Beetles Adapt to a Marginal Host Plant

Genes that affect adaptive traits have been identified, but our knowledge of the genetic basis of adaptation in a more general sense (across multiple traits) remains limited. We combined population-genomic analyses of evolve-and-resequence experiments, genome-wide association mapping of performance traits, and analyses of gene expression to fill this knowledge gap and shed light on the genomics of adaptation to a marginal host (lentil) by the seed beetle Callosobruchus maculatus. Using population-genomic approaches, we detected modest parallelism in allele frequency change across replicate lines during adaptation to lentil. Mapping populations derived from each lentil-adapted line revealed a polygenic basis for two host-specific performance traits (weight and development time), which had low to modest heritabilities. We found less evidence of parallelism in genotype-phenotype associations across these lines than in allele frequency changes during the experiments. Differential gene expression caused by differences in recent evolutionary history exceeded that caused by immediate rearing host. Together, the three genomic datasets suggest that genes affecting traits other than weight and development time are likely to be the main causes of parallel evolution and that detoxification genes (especially cytochrome P450s and beta-glucosidase) could be especially important for colonization of lentil by C. maculatus.

Gene Expression and Diet Breadth in Plant-Feeding Insects: Summarizing Trends

Transcriptomic studies lend insights into the role of transcriptional plasticity in adaptation and specialization. Recently, there has been growing interest in understanding the relationship between variation in herbivorous insect gene expression and the evolution of diet breadth. We review the studies that have emerged on insect gene expression and host plant use, and outline the questions and approaches in the field. Many candidate genes underlying herbivory and specialization have been identified, and a few key studies demonstrate increased transcriptional plasticity associated with generalist compared with specialist species. Addressing the roles that transcriptional variation plays in insect diet breadth will have important implications for our understanding of the evolution of specialization and the genetic and environmental factors that govern insect-plant interactions.

Gut bacteria of the cowpea beetle mediate its resistance to dichlorvos and susceptibility to Lippia adoensis essential oil

Bacteria inhabiting the gut of insects provide many benefits to their hosts, such as aiding in food digestion, reproduction, and immunity, tissue homeostasis, adaptation to environment and resistance to pathogen and pesticides. The cowpea beetle, Callosobruchus maculatus, is a serious cosmopolitan pest of pulses. This beetle has lent itself as a guinea pig for several ecological studies. It harbors a consortium of bacterial communities in its gut, but the evidence for their role in its physiology is fragmentary. In this work, we hypothesized that gut microbiota mediates C. maculatus resistance to dichlorvos (DDVP or O,O-dimethyl O-2,2-dichlorovinylphosphate) and represent the target of Lippia adoensis (Gambian Tea Bush) essential oil (EO). Symbiotic and aposymbiotic beetles were exposed to artificial cowpea seeds earlier treated with DDVP or EO. Adult mortality and changes in gut bacterial community composition and abundance were examined at F1 and F5 generations. The susceptibility of experimental beetles to DDVP was significantly affected by their symbiotic status. The adult mortality decreased across generations in DDVP treatments, and remained significantly higher in aposymbiotic groups. In EO treatments, the mortality was consistent irrespective of symbiotic status and experimental generations. When compared to DDVP and the Control, EO treatments had significantly lower bacterial richness and diversity, as well as lower abundance of Proteobacteria, Firmicutes, and Bacteroidetes. These results support our hypothesis and describe the responses of gut microbial communities to pesticide treatments. This could be of interest for developing new management strategies of this pest.

Characterization of Genomic Variants Associated with Scout and Recruit Behavioral Castes in Honey Bees Using Whole-Genome Sequencing

Among forager honey bees, scouts seek new resources and return to the colony, enlisting recruits to collect these resources. Differentially expressed genes between these behaviors and genetic variability in scouting phenotypes have been reported. Whole-genome sequencing of 44 Apis mellifera scouts and recruits was undertaken to detect variants and further understand the genetic architecture underlying the behavioral differences between scouts and recruits. The median coverage depth in recruits and scouts was 10.01 and 10.7 X, respectively. Representation of bacterial species among the unmapped reads reflected a more diverse microbiome in scouts than recruits. Overall, 1,412,705 polymorphic positions were analyzed for associations with scouting behavior, and 212 significant (p-value < 0.0001) associations with scouting corresponding to 137 positions were detected. Most frequent putative transcription factor binding sites proximal to significant variants included Broad-complex 4, Broad-complex 1, Hunchback, and CF2-II. Three variants associated with scouting were located within coding regions of ncRNAs including one codon change (LOC102653644) and 2 frameshift indels (LOC102654879 and LOC102655256). Significant variants were also identified on the 5’UTR of membrin, and 3’UTRs of laccase 2 and diacylglycerol kinase theta. The 60 significant variants located within introns corresponded to 39 genes and most of these positions were > 1000 bp apart from each other. A number of these variants were mapped to ncRNA LOC100578102, solute carrier family 12 member 6-like gene, and LOC100576965 (meprin and TRAF-C homology domain containing gene). Functional categories represented among the genes corresponding to significant variants included: neuronal function, exoskeleton, immune response, salivary gland development, and enzymatic food processing. These categories offer a glimpse into the molecular support to the behaviors of scouts and recruits. The level of association between genomic variants and scouting behavior observed in this study may be linked to the honey bee’s genomic plasticity and fluidity of transition between castes.

Transcriptomic response of cowpea bruchids to N-acetylglucosamine-specific lectins

Griffonia simplicifolia lectin II (GSII) and wheat germ agglutinin (WGA) are N-acetylglucosamine-binding lectins. Previous studies demonstrated that they have anti-insect activity, a property potentially useful in pest control. To gain some insight into the insect response to dietary lectins, we performed transcriptomic analysis using the cowpea bruchid (Callosobruchus maculatus) midgut microarray platform we built. Compared to the nonnutritional cellulose treatment, dietary lectins induced more profound changes in gene expression. Ingestion of relatively high doses of lectins for 24 h resulted in alteration of gene expression involved in sugar and lipid metabolism, transport, development, defense, and stress tolerance. Metabolic genes were largely downregulated. Moreover, we observed disorganized microvilli resulting from ingestion of WGA. This morphological change is consistent with the lectin-induced changes in genes related to midgut epithelial cell repair. In addition, suboptimal nutrient conditions may serve as a stress signal to trigger senescence processes, leading to growth arrest and developmental delay.

Insect response to plant defensive protease inhibitors

Plant protease inhibitors (PIs) are natural plant defense proteins that inhibit proteases of invading insect herbivores. However, their anti-insect efficacy is determined not only by their potency toward a vulnerable insect system but also by the response of the insect to such a challenge. Through the long history of coevolution with their host plants, insects have developed sophisticated mechanisms to circumvent antinutritional effects of dietary challenges. Their response takes the form of changes in gene expression and the protein repertoire in cells lining the alimentary tract, the first line of defense. Research in insect digestive proteases has revealed the crucial roles they play in insect adaptation to plant PIs and has brought about a new appreciation of how phytophagous insects employ this group of molecules in both protein digestion and counterdefense. This review provides researchers in related fields an up-to-date summary of recent advances.

Expression analysis of two P450 monooxygenase genes of the tobacco cutworm moth (Spodoptera litura) at different developmental stages and in response to plant allelochemicals

Cytochrome P450 monooxygenases (P450s) of insects are known to be involved in the metabolism or detoxification of plant allelochemicals and insecticides. Spodoptera litura (Lepidoptera, Noctuidae) is a polyphagous moth responsible for severe yield losses in many crops. In this study, two full-length P450 genes, CYP6B48 and CYP6B58, were cloned from S. litura. The cDNA sequences encode proteins with 503 and 504 amino acids, respectively. Phylogenetic analysis revealed that CYP6B48 and CYP6B58 belong to the CYP6B subfamily of P450s. Quantitative real-time PCR analyses showed that CYP6B48 and CYP6B58 were expressed only at larval stage, but not at pupal and adult stages. The highest levels of transcripts were found in the midguts and fat bodies of the larvae. No expression was detected in the ovary or hemolymph. Feeding with diets containing cinnamic acid, quercetin, or coumarin did not affect expression of CYP6B48. In contrast, diet supplemented with xanthotoxin dramatically increased the levels of CYP6B48 transcript in the midgut and fat bodies. Larvae fed with flavone had high levels of transcript of CYP6B48 in the midgut, whereas only slightly elevated levels were found in the fat bodies. Effects of the tested allelochemicals on CYP6B58 expression were minor. Hence, our findings show that S. litura responds to specific allelochemicals such as xanthotoxin with the accumulation of CYP6B48 transcripts, suggesting that specific signals in the food control the insect's ability to convert toxic allelochemicals to less harmful forms at the transcriptional level.

Activity of the Antioxidant Defense System in a Typical Bioinsecticide-and Synthetic Insecticide-treated Cowpea Storage Beetle Callosobrochus maculatus F. (Coleoptera: Chrysomelidae)

The non-enzymatic and enzymatic antioxidant defense systems play a major role in detoxification of pro-oxidant endobiotics and xenobiotics. The possible involvement of beetle non-enzymatic [α-tocopherol, glutathione (GSH), and ascorbic acid] and enzymatic [catalase (CAT), superoxide dismutase (SOD), peroxidase (POX), and polyphenol oxidase (PPO)] antioxidant defense system on the insecticidal activity of synthetic insecticides (cypermethrin, 2,2-dicholorovinyl dimethyl phosphate, and λ-cyhalothrin) and ethanolic plant extracts of Tithonia diversifolia, Cyperus rotundus, Hyptis suaveolens leaves, and Jatropha Curcas seeds was investigated. 2,2-Dicholorovinyl dimethyl phosphate (DDVP; 200 ppm, LC₅₀ = 13.24 ppm) and T. diversifolia (20,000 ppm) resulted in 100% beetle mortality at 96-hour post-treatment. The post-treatments significantly increased the beetle α-tocopherol and GSH contents. Activities of CAT, SOD, POX, and PPO were modulated by the synthetic insecticides and bioinsecticides to diminish the adverse effect of the chemical stresses. Quantitative and qualitative allelochemical compositions of bioinsecticides and chemical structure of synthetic insecticides possibly account and for modulation of their respective enzyme activities. Altogether, oxidative stress was enormous enough to cause maladaptation in insects. This study established that oxidative imbalance created could be the molecular basis of the efficacy of both insecticides and bio-insecticides. Two, there was development of functional but inadequate antioxidant defense mechanism in the beetle.

Insecticides and Bio-insecticides Modulate the Glutathione-related Antioxidant Defense System of Cowpea Storage Bruchid (Callosobruchus maculatus)

The possible cellular involvements of cowpea storage bruchid (Callosobruchus maculatus (Fab.) [Coleoptera: Chrysomelidae]) glutathione and its related enzymes system in the cellular defense against insecticides (Cypermethrin and λ-cyhalothrin) and bio-insecticides (ethanolic extract of Tithonia diversifolia, Cyperus rotundus, Hyptis suavolens leaves, and Jatropha curcas seed) were investigated. The results showed that the effect of insecticides and bio-insecticides on the C. maculatus is a function of oxidative and nitrosative stresses generated in vivo. A significant (p < 0.05) increase in carbonyl protein (CP) and lipid peroxidation (LPO) contents in bio-insecticides and insecticides exposed groups compared to the control indicates the extent of vital organs damage. These stresses caused similar and significant increase of glutathione peroxidase and glutathione synthetase in response to insecticides and bio-insecticide exposure in a dose-dependent manner. There was no post-translational modification of glutathione transferases expression induced. The alterations of the insect glutathione-dependent antioxidant enzyme activities reflect the presence of a functional defense mechanism against the oxidative and nitrosative stress and are related firmly to the glutathione demands and metabolism but appear inadequate by the significant reduction in glutathione reductase (GR) activity to prevent the damages. Exogenous application of reduced glutathione (GSH), to complement the in vivo demand, could not protect against the onslaught.

Insecticides and Bio-insecticides Modulate the Glutathione-related Antioxidant Defense System of Cowpea Storage Bruchid (Callosobruchus maculatus)

The possible cellular involvements of cowpea storage bruchid (Callosobruchus maculatus (Fab.) [Coleoptera: Chrysomelidae]) glutathione and its related enzymes system in the cellular defense against insecticides (Cypermethrin and λ-cyhalothrin) and bio-insecticides (ethanolic extract of Tithonia diversifolia, Cyperus rotundus, Hyptis suavolens leaves, and Jatropha curcas seed) were investigated. The results showed that the effect of insecticides and bio-insecticides on the C. maculatus is a function of oxidative and nitrosative stresses generated in vivo. A significant (p < 0.05) increase in carbonyl protein (CP) and lipid peroxidation (LPO) contents in bio-insecticides and insecticides exposed groups compared to the control indicates the extent of vital organs damage. These stresses caused similar and significant increase of glutathione peroxidase and glutathione synthetase in response to insecticides and bio-insecticide exposure in a dose-dependent manner. There was no post-translational modification of glutathione transferases expression induced. The alterations of the insect glutathione-dependent antioxidant enzyme activities reflect the presence of a functional defense mechanism against the oxidative and nitrosative stress and are related firmly to the glutathione demands and metabolism but appear inadequate by the significant reduction in glutathione reductase (GR) activity to prevent the damages. Exogenous application of reduced glutathione (GSH), to complement the in vivo demand, could not protect against the onslaught.

Zero effect of Bt rice on expression of genes coding for digestion, detoxification and immune responses and developmental performances of brown planthopper Nilaparvata lugens (Stål)

Transgenic Cry1Ac, Cry2Aa and Cry1Ca (Bt toxins) rice lines are well developed to manage lepidopteron pests in China. The impact of transgenic Bt rice on the non-target Brown Planthopper (BPH) has become an essential part of environmental risk assessment, however, scanty evidence is found addressing on developmental and molecular responses of BPH to the ingestion of Bt protein from transgenic rice. The focus of the current study is to examine the developmental characteristics and the expression profiles of gene in relation to digestion, detoxification and immune responses were examined. Our study strongly revealed that the tested Bt rice strains have no unfavorable effect on fecundity, survival and growth of BPH. Furthermore, each of the tested genes did not exhibit distinct expression pattern responding to non Bt parental cultivar, thus, it could be concluded that Bt rice have no detrimental effects on the physiological processes of digestion, detoxification and immune responses of BPH.