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.
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.
Xu, Q.-Y., Q.-W. Meng, P. Deng, K.-Y. Fu, W.-C. Guo, and G.-Q. Li. Bulletin of Entomological Research https://doi.org/10.1017/S0007485318001050
Dietary delivery of bacterially expressed double-stranded RNA (dsRNA) has a great potential for management of Leptinotarsa decemlineata. An important first step is to discover possible RNA-interference (RNAi)-target genes effective against larvae, especially the old larvae. In the present paper, five putative Broad-Complex (BrC) cDNAs (Z1-Z4, and Z6) were identified in L. decemlineata. The expression of the five LdBrC isoforms was suppressed by juvenile hormone signaling, whereas the transcription was upregulated by 20-hydroxyecdysone signaling at the fourth (final) instar larval stage. Feeding of bacterially expressed dsBrC (derived from a common fragment of the five LdBrC variants) in the third- and fourth-instar larvae successfully knocked down the target mRNAs. For the fourth-instar LdBrC RNAi hypomorphs, they had a higher larval mortality compared with the controls. Moreover, most dsBrC-fed beetles did not pupate normally. After removal of the apolysed larval cuticle, a miniature adult was found. The adult head, compound eyes, prothorax, mesothorax, metathorax were found on the dorsal view. Distinct adult cuticle pigmentation was seen on the prothorax. The mouthparts, forelegs, midlegs, and hindlegs could be observed on the ventral view of the miniature adults. For the third-instar LdBrC RNAi specimens, around 20% moribund beetles remained as prepupae and finally died. Therefore, LdBrC is among the most attractive candidate genes for RNAi to control the fourth-instar larvae in L. decemlineata.
Kryukov, V. Y., M. R. Kabilov, N. Smirnova, O. G. Tomilova, M. V. Tyurin, Y. B. Akhanaev, O. V. Polenogova, V. P. Danilov, S. K. Zhangissina, T. Alikina, O. N. Yaroslavtseva, V. V. Glupov, Fungal Biology https://doi.org/10.1016/j.funbio.2019.09.012
Strains of entomopathogenic fungi may have substantial differences in their final stages of mycosis. Insect cadavers are usually overgrown with mycelium after colonization of the insect body, but in many cases, bacterial decomposition of the colonized hosts occurs. We used two Metarhizium robertsii strains in the work: Mak-1 (cadavers become overgrown with mycelium and conidia) and P-72 (cadavers decay after fungal colonization). We conducted a comparative analysis of gut and cadaver microbiota in Colorado potato beetle larvae using 16S rRNA gene sequencing after infection with these strains. In addition, we estimated the content of different forms of nitrogen in cadavers and the influence of cadavers on the growth of Solanum lycopersicum on sand substrates under laboratory conditions. It was shown that infections did not lead to a significant shift in the midgut bacterial communities of infected insects compared to those of untreated insects. Importantly, bacterial communities were similar in both types of cadaver, with predominantly enterobacteria. Decomposing cadavers (P-72) were characterized by increased nitrate and ammonium, and they had a stronger growth-promoting effect on plants compared to cadavers overgrown with mycelium and conidia (Mak-1). We also estimated the colonization and growth of plants after treatment with conidia of both strains cultivated on artificial medium. Both cultures successfully colonized plants, but strain P-72 showed stronger growth promotion than Mak-1. We propose that the use of deviant strains that are unable to sporulate on cadavers leads to a faster (though only passive) flow of nitrogen from killed insects to plants.
Krey, K. L., C. K. Blubaugh, J. T. Van Leuven, and W. E. Snyder. Environmental Entomology, nvz123, https://doi.org/10.1093/ee/nvz123
Soil chemistry and microbial diversity can impact the vigor and nutritive qualities of plants, as well as plants’ ability to deploy anti-herbivore defenses. Soil qualities often vary dramatically on organic versus conventional farms, reflecting the many differences in soil management practices between these farming systems. We examined soil-mediated effects on herbivore performance by growing potato plants (Solanum tuberosum L.) in soils collected from organic or conventional commercial farm fields, and then exposing these plants to herbivory by green peach aphids (Myzus persicae Sulzer, Hemiptera: Aphididae) and/or Colorado potato beetles (Leptinotarsa decemlineata Say, Coleoptera: Chrysomelidae). Responses of the two potato pests varied dramatically. Survivorship of Colorado potato beetles was almost 3× higher on plants grown in organic than in conventional soils, but was unaffected by the presence of aphids. In contrast, aphid colony growth was twice as rapid when aphids were reared alone rather than with Colorado potato beetles, but was unaffected by soil type. We saw no obvious differences in soil nutrients when comparing organic and conventional soils. However, we saw a higher diversity of bacteria in organic soils, and potato plants grown in this soil had a lower carbon concentration in foliar tissue. In summary, the herbivore species differed in their susceptibility to soil- versus competitor-mediated effects, and these differences may be driven by microbe-mediated changes in host plant quality. Our results suggest that soil-mediated effects on pest growth can depend on herbivore species and community composition, and that soil management strategies that promote plant health may also increase host quality for pests.