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

Colorado potato 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.

Dumas, P. , M. Sambou , J. D. Gaudet , M. D. Morin , C. E. Moffat , S. Boquel , P. Morin. Archives of Insect Biochemistry and Physiology https://doi.org/10.1002/arch.21642

The Colorado potato beetle (Leptinotarsa decemlineata [Say]) is an insect pest that can significantly harm potato plants worldwide. Control of this insect relies heavily on chemical insecticides such as chlorantraniliprole. Nevertheless, the complete molecular signature associated with response to this compound is lacking in L. decemlineata. In this study, amplification and quantification by qRT‐PCR (quantitative reverse transcription‐polymerase chain reaction) of targets relevant to chlorantraniliprole were undertaken in insects exposed to this chemical. This approach showed modulation of numerous cytochrome P450s, such as CYP350D1 and CYP4Q3, as well as upregulation of microRNAs (miRNAs), including miR‐1‐3p and miR‐305‐5p, in chlorantraniliprole‐exposed insects. Functional assessment of transcript targets predicted to be regulated by these miRNAs was performed and revealed their likely impact on transcriptional regulation. RNAi‐based targeting of CYP350D1 notably provided preliminary evidence of its underlying implication for chlorantraniliprole response in L. decemlineata. Overall, this study strengthens the current knowledge of the molecular changes linked to chlorantraniliprole response in L. decemlineata and provides novel targets with potential relevance to chlorantraniliprole susceptibility in this insect pest of global relevance.

Tomilova, O. G., O. N. Yaroslavtseva, M. D. Ganina, M. V. Tyurin, E. I. Chernyak, I. V. Senderskiy, Y. A. Noskov, O. V. Polenogova, Y. B. Akhanaev, V. Yu. Kryukov, V. V. Glupov, S. V. Morozov. Journal of Insect Physiology 116: 106-117. https://doi.org/10.1016/j.jinsphys.2019.05.003

Susceptibility to the fungus Metarhizium robertsii and changes in host defences were evaluated in different stages of the intermoult period (4–6 h, 34–36 h and 84–86 h post moult in IV larval instars) of the Colorado potato beetle. A significant thickening of the cuticle during larval growth was accompanied by decreases in cuticle melanization, phenoloxidase activity and epicuticular hydrocarbon contents (C28-C32). At the same time, a decrease in the conidial adhesion rate and an increase in resistance to the fungus were observed. In addition, we recorded significant elevation of the encapsulation rate and total haemocyte counts in the haemolymph during the specified period. The activity of detoxification enzymes decreased in the haemolymph but increased in the fat body during larval growth. No significant differences in the fatty acid content in the epicuticle were observed. The role of developmental disorders in susceptibility to entomopathogenic fungi is also discussed.

Margus, A., Piiroinen, S., Lehmann, P. et al. Scientific Reports 9, 11320 (2019) doi:10.1038/s41598-019-47473-1

Stress tolerance and adaptation to stress are known to facilitate species invasions. Many invasive species are also pests and insecticides are used to control them, which could shape their overall tolerance to stress. It is well-known that heavy insecticide usage leads to selection of resistant genotypes but less is known about potential effects of mild sublethal insecticide usage. We studied whether stressful, sublethal pyrethroid insecticide exposure has within-generational and/or maternal transgenerational effects on fitness-related traits in the Colorado potato beetle (Leptinotarsa decemlineata) and whether maternal insecticide exposure affects insecticide tolerance of offspring. Sublethal insecticide stress exposure had positive within-and transgenerational effects. Insecticide-stressed larvae had higher adult survival and higher adult body mass than those not exposed to stress. Furthermore, offspring whose mothers were exposed to insecticide stress had higher larval and pupal survival and were heavier as adults (only females) than those descending from control mothers. Maternal insecticide stress did not explain differences in lipid content of the offspring. To conclude, stressful insecticide exposure has positive transgenerational fitness effects in the offspring. Therefore, unsuccessful insecticide control of invasive pest species may lead to undesired side effects since survival and higher body mass are known to facilitate population growth and invasion success.