Wang Y., Y. Li, G. Li, P. Wan, C. Li. J Econ Entomol. 2019;112(2):912-923. doi: 10.1093/jee/toy396.
Structural cuticular proteins (CPs) are the primary components of insect cuticle, linings of salivary gland, foregut, hindgut and tracheae, and midgut peritrophic membrane. Variation of CPs in insect cuticle can cause penetration resistance to insecticides. Moreover, depletion of specific CP by RNA interference may be a suitable way for the development of potential pest control traits. Leptinotarsa decemlineata (Say) CPs are poorly characterized at present, and therefore, we mined the genome and transcriptome data to better annotate and classify L. decemlineata CPs in this study, by comparison with the annotated CPs of Tribolium castaneum Browse (Coleoptera: Tenebrionidae). We identified 175 CP genes. Except one miscellaneous CP with an 18-amino acid motif, these CPs were classified into 7 families based on motifs and phylogenetic analyses (CPs with a Rebers and Riddiford motif, CPR; CPs analogous to peritrophins, CPAP3 and CPAP1; CPs with a tweedle motif, TWDL; CPs with a 44-amino acid motif, CPF; CPs that are CPF-like, CPFL; and CPs with two to three copies of C-X5-C motif, CPCFC). Leptinotarsa decemlineata CPRs could be categorized into three subfamilies: RR-1 (50), RR-2 (85), and RR-3 (2). The RR-1 proteins had an additional motif with a conserved YTADENGF sequence. The RR-2 members possessed a conserved RDGDVVKG region and three copes of G-x(3)-VV. Few genes were found in TWDL (9), CPAP1 (9), CPAP3 (8), CPF (5), CPFL (4), and CPCFC (2) families. The findings provide valuable information to explore molecular modes of penetration resistance to insecticides and to develop dsRNA-based control method in L. decemlineata.
Tigreros N, Wang EH, Thaler JS. Funct Ecol. 2018;32(4):982-989. doi: 10.1111/1365-2435.13046.
Prey species can respond to the risk of predation with a range of antipredator behaviours and physiological changes. While these responses increase chances of survival, they often involve feeding reductions and greater energy expenditure (e.g. increases in metabolic rate). As a consequence, a prey response is constrained by its own nutritional condition. While a number of studies indeed demonstrate that prey in better nutritional condition have stronger antipredator behaviours, we do not yet understand how condition impacts the physiological component of the prey's response. Previous research revealed that Leptinotarsa decemlineata beetles experiencing predation risk improve their offspring's nutritional condition by promoting intraclutch egg cannibalism. Importantly, egg cannibalism decreased offspring vulnerability by increasing larval behavioural responses to chronic predation risk. In this study we test if egg cannibalism similarly impacts larval physiological responses by comparing how risk of predation in cannibals and non-cannibals affects their behaviour (e.g. feeding reductions), metabolic rate and energy stores. We found that non-cannibals did not exhibit antipredator behaviours but responded physiologically, by increasing metabolic rates. In contrast, cannibals responded behaviourally, suppressing feeding, but without altering metabolism. While cannibals and non-cannibals coupled food intake and energy expenditure differently, both reached similar growth rates and had similar energy stores when facing chronic predation risk. These results indicate that increases in predator avoidance behaviours are not merely mirrored by a stronger physiological response. Instead, changes in metabolism appear to ameliorate, within our experimental conditions, the costs associated with the behavioural response. Prey in poorer nutritional state are not less responsive to predators but appear to rely more heavily on physiological responses, demonstrating that how prey integrates behaviour and physiology depends on their own nutritional state.
Wu JJ, Chen ZC, Wang YW, Fu KY, Guo WC, Li GQ. Insect Mol Biol. 2019;28(1):52-64.
Insect chitin deacetylases (CDAs) are carbohydrate esterases that catalyze N-deacetylation of chitin to generate chitosan, a process essential for chitin organization and compactness during the formation of extracellular chitinous structure. Here we identified two CDA2 splice variants (LdCDA2a and LdCDA2b) in Leptinotarsa decemlineata. Both splices were abundantly expressed in larval foregut, rectum, and epidermis; their levels peaked immediately before ecdysis within each instar. In vivo results revealed that the two isoforms transcriptionally responded, positively and negatively respectively, to 20-hydroxyecdysone and juvenile hormone signaling pathways. RNA interference (RNAi)-aided knockdown of the two LdCDA2 variants (hereafter LdCDA2) or LdCDA2b, rather than LdCDA2a, resulted in three negative effects. First, foliage consumption was significantly reduced, larval developing period was lengthened, and larval growth was retarded. Second, chitin contents were reduced, whereas glucose, trehalose, and glycogen contents were increased in the LdCDA2 and LdCDA2b RNAi larvae. Third, approximately 20% of LdCDA2 and LdCDA2b RNAi larvae were trapped within the exuviae and finally died. About 60% of the abnormal pupae died as pharate adults. Around 20% of the RNAi pupae emerged as deformed adults, with small size and wrinkled wings. These adults eventually died within 1 week after molting. Our results reveal that knockdown of CDA2 affects chitin accumulation. Consequently, LdCDA2 may be a potential target for control of L. decemlineata larvae.
Chertkova EA, Grizanova EV, Dubovskiy IM. J Invertebr Pathol. 2018;153:203-206. doi: 10.1016/j.jip.2018.02.020.
Dopamine (DA) is known as a hormone neurotransmitter molecule involved in several stress reactions in both vertebrates and invertebrates. Following infections with the fungi Metarhizium robertsii or Beauveria bassiana and the bacterium Bacillus thuringiensis, dopamine the concentration was measured at different time points in the haemolymph of the Colorado potato beetle, Leptinotarsa decemlineata and the larvae of the greater wax moth Galleria mellonella. The infection with M. robertsii increased (4 to 12-fold) DA concentrations in the haemolymph of the potato beetle larvae and the oral infection by B. thuringiensis also lead to a 30 and 45-fold increase. During infection of the greater wax moth larvae with Beauveria bassiana and B. thuringiensis DA increased 4 to 20-fold and about 2 to 2,5-fold respectively, compared to non-infected insects. The relative DA concentrations varied between the two insects and depended on the pathogens and post infection time.
Kaplanoglu E, Chapman P, Scott IM, Donly C. Scientific Reports. 2017;7(5):1762. doi: 10.1038/s41598-017-01961-4.
Current control of insect pests relies on chemical insecticides, however, insecticide resistance development by pests is a growing concern in pest management. The main mechanisms for insecticide resistance typically involve elevated activity of detoxifying enzymes and xenobiotic transporters that break-down and excrete insecticide molecules. In this study, we investigated the molecular mechanisms of imidacloprid resistance in the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), an insect pest notorious for its capacity to develop insecticide resistance rapidly. We compared the transcriptome profiles of imidacloprid-resistant and sensitive beetle strains and identified 102 differentially expressed transcripts encoding detoxifying enzymes and xenobiotic transporters. Of these, 74 were up-regulated and 28 were down-regulated in the resistant strain. We then used RNA interference to knock down the transcript levels of seven up-regulated genes in the resistant beetles. Ingestion of double-stranded RNA successfully knocked down the expression of the genes for three cytochrome P450s (CYP6BQ15, CYP4Q3 and CYP4Q7), one ATP binding cassette (ABC) transporter (ABC-G), one esterase (EST1), and two UDP-glycosyltransferases (UGT1 and UGT2). Further, we demonstrated that silencing of CYP4Q3 and UGT2 significantly increased susceptibility of resistant beetles to imidacloprid, indicating that overexpression of these two genes contributes to imidacloprid resistance in this resistant strain.
Chung SH, Scully ED, Peiffer M, et al. Scientific Reports. 2017;7(1):39690. doi: 10.1038/srep39690.
Herbivore associated bacteria are vital mediators of plant and insect interactions. Host plants play an important role in shaping the gut bacterial community of insects. Colorado potato beetles (CPB; Leptinotarsa decemlineata) use several Solanum plants as hosts in their natural environment. We previously showed that symbiotic gut bacteria from CPB larvae suppressed jasmonate (JA)-induced defenses in tomato. However, little is known about how changes in the bacterial community may be involved in the manipulation of induced defenses in wild and cultivated Solanum plants of CPB. Here, we examined suppression of JA-mediated defense in wild and cultivated hosts of CPB by chemical elicitors and their symbiotic bacteria. Furthermore, we investigated associations between the gut bacterial community and suppression of plant defenses using 16 S rRNA amplicon sequencing. Symbiotic bacteria decreased plant defenses in all Solanum hosts and there were different gut bacterial communities in CPB fed on different host plants. When larvae were reared on different hosts, defense suppression differed among host plants. These results demonstrate that host plants influence herbivore gut bacterial communities and consequently affect the herbivore's ability to manipulate JA-mediated plant defenses. Thus, the presence of symbiotic bacteria that suppress plant defenses might help CPB adapt to host plants.
Tajmiri P, Fathi SAA, Golizadeh A, Nouri-Ganbalani G. Int J Pest Manage. 2017;63(4):273-279.
Intercropping systems are practiced to reducing pest density, enhancing predator's diversity and stabling crop yield. We evaluated the effect of strip-intercropping potato and annual alfalfa on populations of Leptinotarsa decemlineata (Say), predator's biodiversity and potato yield over two seasons (2014 and 2015). Our results revealed that the densities of egg masses, eggs, larvae and adults of Colorado potato beetle (CPB) were significantly lower in intercrops than in monoculture. The main CPB predators recorded on potato plants (ladybirds and the green lacewing) showed a significant increase in the density at each of the three intercrops than in monoculture. The percentage of dry tubers weight loss was 40.9%-42.6% in monoculture, 16.3%-18.7% in 6P: 2A and <10% in 2P: 2A and 4P: 2A in two studied years. Our results suggest that strip-intercropping potato with annual alfalfa, particularly in 2P: 2A and 4P: 2A patterns may be an effective way in integrated management of CPB for reducing pest density, enhancing the presence of predators in potato fields and improving potato yield.
Morin MD, Frigault JJ, Lyons PJ, et al. Insect Mol Biol. 2017;26(5):574-583. doi: 10.1111/imb.12320.
The Colorado potato beetle [Leptinotarsa decemlineata (Say)] is an important insect pest that can inflict considerable damage to potato plants. This insect can survive extended periods of cold exposure, and yet the molecular switches underlying this phenomenon have not been fully elucidated. A better characterization of this process would highlight novel vulnerabilities associated with L. decemlineata that could serve as targets for the management of this devastating pest. Using high-throughput sequencing, the current work reveals a cold-associated signature group of microRNAs (miRNAs) in control (15°C) and -5°C-exposed L. decemlineata. The results show 42 differentially expressed miRNAs following cold exposure including miR-9a-3p, miR-210-3p, miR-276-5p and miR-277-3p. Functional analysis of predicted targets associated with these cold-responsive miRNAs notably linked these changes with vital metabolic and cellular processes. Overall, this study highlights the miRNAs probably responsible for facilitating cold adaptation in L. decemlineata and implicates miRNAs as a key molecular target to consider in the development of novel pest management strategies against these insects.
Hermann SL, Thaler JS. Oecologia. 2018;188(4):945-952. doi: 10.1007/s00442-018-4202-7.
Predator-prey interactions primarily focus on prey life-stages that are consumed. However, animals in less vulnerable life-stages might also be influenced by the presence of a predator, making our understanding of predation-related impacts across all life-stages of prey essential. It has been previously demonstrated that Podisus maculiventris is a voracious predator of eggs and larvae of Leptinotarsa decemlineata, and that larvae will alter their behavior to avoid predation. However, the adult beetles are not readily consumed by P. maculiventris, raising the question of whether they will respond to predators to protect themselves or their offspring. Here, we examine the effect of predation risk by P. maculiventris, on three adult behaviors of L. decemlineata; colonization, oviposition, and feeding, and the resulting impact on host plant damage. In an open-field test, there was no difference in natural beetle colonization between plots with predation risk and control treatments. However, subsequent host plant damage by adult beetles was 63.9% less in predation risk treatments. Over the lifetime of adult beetles in field mesocosms, per capita feeding was 23% less in the predation risk treatment. Beetle oviposition was 37% less in the presence of predators in a short-term, greenhouse assay, and marginally reduced in longer term field mesocosms. Our results indicate that predation risk can drive relatively invulnerable adult herbivores to adjust behaviors that affect themselves (feeding) and their offspring (oviposition). Thus, the full impact of predator presence must be considered across the prey life cycle.
Clements J, Sanchez-Sedillo B, Bradfield CA, Groves RL. PLoS ONE. 2018;13(10):e0205881. doi: 10.1371/journal.pone.0205881.
The Colorado potato beetle, Leptinotarsa decemlineata (Say), is an agricultural pest of commercial potatoes in parts of North America, Europe, and Asia. Plant protection strategies within this geographic range employ a variety of pesticides to combat not only the insect, but also plant pathogens. Previous research has shown that field populations of Leptinotarsa decemlineata have a chronological history of resistance development to a suite of insecticides, including the Group 4A neonicotinoids. The aim of this study is to contextualize the transcriptomic response of Leptinotarsa decemlineata when exposed to the neonicotinoid insecticide imidacloprid, or the fungicides boscalid or chlorothalonil, in order to determine whether these compounds induce similar detoxification mechanisms. We found that chlorothalonil and imidacloprid induced similar patterns of transcript expression, including the up-regulation of a cytochrome p450 and a UDP-glucuronosyltransferase transcript, which belong to protein families associated with xenobiotic metabolism. Further, transcriptomic responses varied among individuals within the same treatment group, suggesting individual insects' responses vary within a population and may cope with chemical stressors in a variety of manners.