Ashouri S, Farshbaf Pourabad R. 2021. Gene. 766:145159.
Considering the relevance of insect α-amylases and natural α-amylase inhibitors present in plants to protect against insect damage, we investigated the effect of white bean and rapeseed protein extracts on digestive α-amylase gene expression of the Colorado potato beetle, Leptinotarsa decemlineata (Say). For this purpose, in vitro and in vivo trials were performed to determine the inhibitory activity of seed proteins on the third and fourth instar larvae. In both trials, the significant inhibitory effect of each extracts on the third and fourth instar larval α-amylase activity and considerable mortality in treatments were observed compared to control trials. In the RT-qPCR, expression ratio demonstrated that the α-amylase gene of two different larval stages grown on both proteins treated leaves had significantly differentiated expression and was up-regulated in third instar larvae and down-regulated in fourth instar larvae compared to control. Results suggest that the hyper-production of α-amylase in third instar larvae is elicited to compensate for the enzyme activity inhibition at an earlier stage and also down-regulation suggests the existence of a negative feedback of plant proteins on the last instar larvae via impaired food intake and digestive α-amylase activity in Colorado potato beetle. Therefore, disruption of the insect's digestive physiology by plant defensive proteins can be considered in the development of innovative controlling methods of this crucial potato pest.
Aflitto NC, Thaler JS. 2020. Ecological Entomology. 45(5):1190–1199.
The influence of predator cues on the behaviour of prey is well supported in the literature; however, a clear understanding of how predator cues affect prey in variable environmental conditions and over longer time scales is needed to better understand the underlying mechanisms. Here, we measure how predator odors affect herbivore colonization, abundance, oviposition, and plant damage across two growing seasons. The study system consisted of Leptinotarsa decemlineata (Colorado potato beetle) as prey, and the aggregation pheromone of live Podisus maculiventris (spined soldier bug) as the predator cue in a potato field. In 2016, the amount of feeding damage by early beetle colonists was lower in predator odor-treated plots, reducing plant damage by 22%. Larval abundance was also reduced in treated plots in 2016. Beetle abundance and damage in 2017 was similar in the treatment and control plots. Two mechanisms were investigated to better understand why prey response to the predator odor treatment weakened over the first season, including changes in predator odor cue strength and prey habituation. Predator odor cue strength emerged as a likely explanation, as dispensers, which released a synthetic predator pheromone over the entire season, reduced the probability of finding damage more consistently than the live predator treatment. These results suggest that temporal patterns of predator cue release and strength may drive prey response across the season, underscoring the importance of cue release-rate and consistency in both species interactions and for the future application of modifying insect behaviour using non-consumptive effects in agricultural systems.
Mehlhorn, S.G., S. Geibel, G. Bucher, R. Nauen. Pesticide Biochemistry and Physiology, Volume 166, June 2020, 104569, https://doi.org/10.1016/j.pestbp.2020.104569
In recent years, substantial effort was spent on the exploration and implementation of RNAi technology using double-stranded RNA (dsRNA) for pest management purposes. However, only few studies investigated the geographical variation in RNAi sensitivity present in field-collected populations of the targeted insect pest. In this baseline study, 2nd instar larvae of 14 different European populations of Colorado potato beetle (CPB), Leptinotarsa decemlineata, collected from nine different countries were exposed to a foliarly applied diagnostic dose of dsactin (dsact) to test for possible variations in RNAi response. Only minor variability in RNAi sensitivity was observed between populations. However, the time necessary to trigger a dsRNA-mediated phenotypic response varied significantly among populations, indicated by significant differences in mortality figures obtained five days after treatment. An inbred German laboratory reference strain D01 and a Spanish field strain E02 showed almost 100% mortality after foliar exposure to 30 ng dsactin (equal to 0.96 g/ha), whereas another Spanish strain E01 was least responsive and showed only 30% mortality. Calculated LD50-values for foliarly applied dsact against strains D01 (most sensitive) and E01 (least sensitive) were 9.22 and 68.7 ng/leaf disc, respectively. The variability was not based on target gene sequence divergence or knock-down efficiency. Variability in expression of the core RNAi machinery genes dicer (dcr2a) and argonaute (ago2a) was observed but did not correlate with sensitivity. Interestingly, RT-qPCR data collected for all strains revealed a strong correlation between the expression level of dcr2a and ago2a (r 0.93) as well as ago2a and stauC (r 0.94), a recently described dsRNA binding protein in Coleopterans. Overall, this study demonstrates that sensitivity of CPB to sprayable RNAi slightly varies between strains but also shows that foliar RNAi as a control method works against all tested CPB populations collected across a broad geographic range in Europe. Thus, underpinning the potential of RNAi-based CPB control as a promising component in integrated pest management (IPM) and resistance management programs.
Gómez-Gallego, C., M. J. Rainio, M. C. Collado, A. Mantziari, S. Salminen, K. Saikkonen, M. Helander, FEMS Microbiology Letters, Volume 367, Issue 6, March 2020, fnaa050, https://doi.org/10.1093/femsle/fnaa050
Here, we examined whether glyphosate affects the microbiota of herbivores feeding on non-target plants. Colorado potato beetles (Leptinotarsa decemlineata) were reared on potato plants grown in pots containing untreated soil or soil treated with glyphosate-based herbicide (GBH). As per the manufacturer's safety recommendations, the GBH soil treatments were done 2 weeks prior to planting the potatoes. Later, 2-day-old larvae were introduced to the potato plants and then collected in two phases: fourth instar larvae and adults. The larvae's internal microbiota and the adults’ intestinal microbiota were examined by 16S rRNA gene sequencing. The beetles’ microbial composition was affected by the GBH treatment and the differences in microbial composition between the control and insects exposed to GBH were more pronounced in the adults. The GBH treatment increased the relative abundance of Agrobacterium in the larvae and the adults. This effect may be related to the tolerance of some Agrobacterium species to glyphosate or to glyphosate-mediated changes in potato plants. On the other hand, the relative abundances of Enterobacteriaceae, Rhodobacter, Rhizobium and Acidovorax in the adult beetles and Ochrobactrum in the larvae were reduced in GBH treatment. These results demonstrate that glyphosate can impact microbial communities associated with herbivores feeding on non-target crop plants.
Wiebe K F, O O Elebute, C M R LeMoine, B J Cassone, Journal of Economic Entomology, Volume 113, Issue 3, June 2020, Pages 1445–1454, https://doi.org/10.1093/jee/toaa020
The Colorado potato beetle (Leptinotarsa decemlineata (Say)) is an important pest of the cultivated potato (Solanum tuberosum (L.) [Solanales: Solanaceae]). With its broad resistance toward commonly used insecticides, it is clear that more sophisticated control strategies are needed. Due to their importance in insect development, microRNAs (miRNAs) represent a potential tool to employ in insect control strategies. However, most studies conducted in this area have focused on model species with well-annotated genomes. In this study, next-generation sequencing was used to catalogue the miRNAs produced by L. decemlineata across all eight stages of its development, from eggs to adults. For most stages, the length of miRNAs peaked between 21 and 22 nt, though it was considerably longer for the egg stage (26 nt). Global profiling of miRNAs revealed three distinct developmental clusters: 1) egg stage; 2) early stage (first, second, and third instar); and 3) late stage (fourth instar, prepupae, pupae, and adult). We identified 86 conserved miRNAs and 33 bonafide novel miRNAs, including stage-specific miRNAs and those not previously identified in L. decemlineata. Most of the conserved miRNAs were found in multiple developmental stages, whereas the novel miRNAs were often stage specific with the bulk identified in the egg stage. The identified miRNAs have a myriad of putative functions, including growth, reproduction, and insecticide resistance. We discuss the putative roles of some of the most notable miRNAs in the regulation of L. decemlineata development, as well as the potential applications of this research in Colorado potato beetle management.
Favell, G.; McNeil, J.N.; Donly, C. Insects 2020, 11, 135.
The Colorado potato beetle, Leptinotarsa decemlineata (Say), is a significant agricultural pest that has developed resistance to many insecticides that are used to control it. Investigating the mechanisms of insecticide detoxification in this pest is important for ensuring its continued control, since they may be contributors to such resistance. Multidrug resistance (MDR) genes that code for the ABCB transmembrane efflux transporters are one potential source of insecticide detoxification activity that have not been thoroughly examined in L. decemlineata. In this study, we annotated the ABCB genes found in the L. decemlineata genome and then characterized the expression profiles across midgut, nerve, and Malpighian tubule tissues of the three full transporters identified. To investigate if these genes are involved in defense against the macrocyclic lactone insecticide ivermectin in this insect, each gene was silenced using RNA interference or MDR protein activity was inhibited using a chemical inhibitor, verapamil, before challenging the insects with a dose of ivermectin. Survival of the insects did not significantly change due to gene silencing or protein inhibition, suggesting that MDR transporters do not significantly contribute to defense against ivermectin in L. decemlineata.
Weber, D.C., Duan, J.J. & Haber, A.I. 2020 J Pest Sci https://doi.org/10.1007/s10340-019-01181-x
For Colorado potato beetle, an integrated approach including semiochemicals and other nonpesticidal tactics is essential to sustainable management. A volatile aggregation pheromone produced by male adult beetles is attractive to both females and males. Yet earlier research also indicates that males respond to a yet-unidentified female-produced sex pheromone. We investigated male Colorado potato beetle behavior on potato plants that had been exposed to females only, males only, mixed-sex groups, or no beetles (clean plants). During observation, these plants hosted no beetles except for the single experimental male beetle. These males (previously mated or unmated) responded very differently to female-exposed plants, spending longer time on these plants, undertaking characteristic active searching behavior, exploring more leaves per plant, and moving more rapidly between leaves, compared to male-exposed or unexposed plants. When presented with a three-way choice, males spent about five times longer on the female-exposed foliage, compared to either male-exposed or clean leaves. Searching parameters differed between mated and unmated males, but both showed similar reactions to female-exposed plants; there was little to no statistical interaction between male mated condition and plant treatment. Results strongly indicate the presence of a persistent female-produced pheromone significantly influencing male searching behavior and between-plant movement.
Gui S, C Taning, D Wei, G Smagghe. 2020. Journal of Insect Physiology 121, 104013. https://doi.org/10.1016/j.jinsphys.2020.104013
Leptinotarsa decemlineata (Say), commonly known as the Colorado potato beetle (CPB), is an agricultural important pest for potatoes and other solanaceous plants. The CRISPR/Cas system is an efficient genome editing technology, which could be exploited to study the biology of CPB and possibly also lead to the development of better environmentally friendly pest management strategies. However, the use of CRISPR/Cas9 has been limited to only a few model insects. Here, for the first time, a CRISPR/Cas9 protocol for mutagenesis studies in CPB was developed. A gene with a clear phenotype such as the vestigial gene (vest), known to be involved in wing development in other insect species, was selected as a good indicator for the knockout study. First, vest was functionally characterized in CPB by using RNAi technology for knockdown studies. Once the expected deformed wing phenotypes were observed, a CRISPR/Cas9 work flow was established for mutagenesis in CPB. By co-injecting the Cas9 protein and a vest-guide RNA into 539 CPB eggs of <1 h old, sixty-two successfully developed to adults, among which mutation in the vest loci was confirmed in 5 of the 18 wingless CPBs (29% phenotypic mutation efficiency). The mutation in vest resulted in a clear phenotype in the CPBs, which developed to adulthood with no hindwing and elytron formed. Altogether, this study provides for the first time a useful methodology involving the use of the CRISPR/Cas9 system for mutagenesis studies in one of the most important pest insects.
Wang, J., Z. Gao, M. Yang, R. Xue, H. Yan, K. Fu, Z. Zhang, W. Guo, G. W. Felton, and R. Zeng. Journal of Pest Science, https://doi.org/10.1007/s10340-019-01173-x
beetle (CPB; Leptinotarsa decemlineata)
has been detected in Xinjiang, China, since 1993 and has caused serious damage
to potato production during its eastward expansion to new geographic ranges.
Symbiotic bacteria often play an essential role for insects to exploit novel
food sources and expand into otherwise inaccessible ecological niches. An
important yet unresolved question is whether herbivore populations from
different geographic ranges have distinct or equal abilities to adapt to
plant-induced defenses. We examined whether two geographic CPB populations
collected from Urumqi and Ili varied in triggering induced defenses in potato
plants, and the results demonstrated that plants damaged by Ili CPB larvae
showed higher levels/activities of the defensive protein polyphenol oxidase
(PPO) than those damaged by Urumqi CPB larvae. Intriguingly, application of
oral secretions (OS) from Ili CPB larvae triggered higher PPO activity in
potato compared with the treatments by OS collected from Urumqi larvae.
Moreover, higher counts of bacterial colonies were observed in Urumqi CPB
larvae by traditional culturing and quantitative PCR. Comparing the gut
bacterial composition of CPB individuals by 16S rRNA amplicon sequencing also
revealed higher abundance and diversity of gut-associated bacteria in the
Urumqi population than that in the Ili population. These results indicate that
the gut bacteria of CPB larvae were geographically shaped during the process of
invasion, which played an important role in mediating plant–insect interactions
and possesses a great potential to drive further invasion.
Skuhrovec, J., O. Douda, M. Zouhar, M. Maňasová, M. Božik, and P. Klouček. Journal of Economic Entomology, toz279, https://doi.org/10.1093/jee/toz279
The Colorado potato beetle ranks as one of the most important potato pests, mainly due to its high feeding rate during all developmental stages, particularly third and fourth larval instar, and high fecundity. The effect of essential oil (EO) from anise (Pimpinella anisum L. [Apiales: Apiaceae]) prepared as conventional and encapsulated (EN) formulations on the mortality and antifeedant responses of young larvae of Colorado potato beetles was studied to evaluate the insecticidal and antifeedant effects of five concentrations of this EO and to assess the persistence of both formulations on potato plants. The EN formulation had a significantly higher residual amount compared with that of the conventionally formulated EO. Significantly different values of LC50 and LC90 (ppm) were established for the EO (LC50 = 1,700 and LC90 = 9500) and EN (LC50 = 3,100 and LC90 = 14,300) formulations. The effects of both P. anisum formulations (EO and EN) applied topically to Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae) larvae were distinctly different from those observed with the contact treatment. At the highest concentration of 20,000 ppm, the mortality of the second instars of the L. decemlineata larvae did not exceed 25%. On the other hand, both tested formulations of P. anisum were highly effective when administered orally. The encapsulated EO formulation achieved a distinctly higher biological activity. Our results confirm that the EO from P. anisum, especially the encapsulated formulation, has high insecticidal properties that may lead to the development of new organic products for the control of Colorado potato beetles.