Xu QY, Meng QW, Deng P, Fu KY, Guo WC, Li GQ. Insect Mol Biol. 2018;27(4):439-453. doi: 10.1111/imb.12384.
Two Drosophila melanogaster E-twenty-six domain transcription factor isoforms (E74A and E74B) act differentially at the start of the 20-hydroxyecdysone (20E) signalling cascade to regulate larval-pupal metamorphosis. In the present paper, we identified the two isoforms (LdE74A and LdE74B) in Leptinotarsa decemlineata. During the larval development stage, the mRNA transcript levels of the two LdE74 isoforms were correlated with circulating 20E titres. In vitro midgut culture and in vivo dietary supplementation with 20E revealed that the presence of 20E induced expression peaks of both LdE74A and LdE74B, with similar patterns observed for the two isoforms. Moreover, the mRNA transcript levels of both LdE74A and LdE74B isoforms were significantly downregulated in the L. decemlineata ecdysone receptor RNA interference (RNAi) specimens, but not in the LdE75 RNAi beetles. Ingestion of 20E reduced the larval fresh weights and shortened the larval development period, irrespective of knockdown of LdE74 or not. RNAi of LdE74 did not affect 20E-induced expression of the Ecdysone induced protein 75-hormone receptor 3-fushi tarazu factor 1 (E75-HR3-FTZ-F1) transcriptional cascade. Thus, it seems that LdE74 mediates 20E signalling independent of the E75-HR3-FTZ-F1 transcriptional cascade. Furthermore, silencing of both LdE74 isoforms caused failure of ecdysis. Most of the LdE74 RNAi beetles remained as prepupae. The LdE74 RNAi prepupae exhibited adult character-like forms underneath after removal of the apolysed larval cuticle. Their appendages such as antennae, legs and wings were shorter than those of control larvae. Only a few LdE74 RNAi larvae finally became deformed pupae, with shortened antennae and legs. Therefore, LdE74 is required for larval-pupal metamorphosis and appendage growth in L. decemlineata.
Hufnagel M, Schilmiller AL, Ali J, Szendrei Z. Ecol Entomol. 2017;42(1):33-41.
Maternal preference is a dynamic process and interactions between preference and performance are fundamental for understanding evolutionary ecology and host association in insect-plant interactions. In the present study, the hypothesis of preference-performance was tested by offering solanaceous specialist Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae) larvae and adult females four plant congeners that ranged in suitability. Larval feeding, development, oviposition, plant glycoalkaloids, and headspace volatiles in the four plant species were analysed to examine the extent of variation, which might explain performance-preference differences. It was found that larval performance was mismatched with adult oviposition preferences. Adults laid more eggs on Solanum immite Dunal plants, which were poor hosts for larval development, feeding, and survival, compared to the other three Solanum species. Chemical plant defenses, in general, did not correlate with performance or preference, but some plant volatiles may have played a role in resolving female choice. Glycoalkaloids such as solanine and chaconine were detected in similar amounts in preferred and non-preferred hosts, but there was significantly more limonene in the headspace of S. immite than in S. tuberosum L. The present findings suggest that we must consider the risk-spreading hypothesis in cases where preference and performance are not positively correlated, particularly in specialist herbivores that can feed on a diversity of congener plants and may attempt to expand their exploits to other solanaceae species.
Kryukov VY, Tomilova OG, Luzina OA, et al. Pest Manag Sci. 2018;74(3):598-606.
BACKGROUND: The search for compounds that interact synergistically with entomopathogenic fungi is aimed at enhancing the efficacy and stability of biological products against pest insects, for example, against the Colorado potato beetle (CPB). We hypothesized that fluorine-containing derivatives of usnic acid (FUA) might be candidates for the development of multicomponent bio-insecticides. The aim of this study was to analyze the co-influence of FUA and Beauveria bassiana on the survival and immune-physiological reactions of CPB larvae. RESULTS: Synergy between FUA and B. bassiana was observed after treatment of second, third and fourth larvae instars under laboratory conditions. Furthermore, synergy was observed in field trials in continental climate conditions in southeastern Kazakhstan. In a field experiment, the median lethal time was shortened three-fold, and cumulative mortality for 15 days increased by 36% in the combined treatment compared with a fungal infection alone. FUA treatment delayed larval development, decreased the total hemocyte count, and increased both the phenoloxidase activity in integuments and the detoxification enzyme rate in hemolymph. A combined treatment with fungus and FUA led to increases in the aforementioned changes. CONCLUSION: Toxicosis caused by FUA provides a stable synergistic effect between FUA and B. bassiana. The combination can be promising for the development of highly efficient products against CPB.
Crossley MS, Rondon SI, Schoville SD. American Journal of Potato Research. 2018;95(5):495-503. doi: 10.1007/s12230-018-9654-0.
The Colorado potato beetle, Leptinotarsa decemlineata Say, is a serious pest of potato, Solanum tuberosum L., worldwide. Leptinotarsa decemlineata has a history of repeated adaptation to insecticides, and exhibits a geographic pattern of decreasing insecticide resistance from east to west in the USA. Imidacloprid is one of the most widely used insecticide in western states. In this study, we measured imidacloprid resistance among larval and adult L. decemlineata from ten locations in the Columbia Basin (southeastern Washington and northeastern Oregon) using topical LD50 bioassays, and compared them to estimates from ten locations in Minnesota and Wisconsin. Larval and adult imidacloprid LD50's and mean percent mortality were generally lowest in Washington and Oregon, but some sites exhibited reductions in mortality comparable to those observed at some Wisconsin sites. Adult LD50's suggest L. decemlineata in the Columbia Basin may be evolving in response to selection by neonicotinoid insecticides, but larval data suggest high susceptibility to imidacloprid remains in most populations. Future work should expand resistance monitoring efforts to include more regions in the West and other insecticide modes of action.
QingWei M, JingJing W, JiFeng S, WenChao G, GuoQing L. American Journal of Potato Research. 2018;95(5):463-472. doi: 10.1007/s12230-018-9646-0.
The potential of teflubenzuron was assessed in a series of laboratory studies in order to achieve consistent, long-term, integrated management of the Colorado potato beetle, Leptinotarsa decemlineata (Say). Teflubenzuron exhibited excellent stomach toxicity to the larvae. Its larvicidal activity was comparable with those of cyhalothrin, chlorantraniliprole and spinosad. Moreover, the teflubenzuron-fed larvae consumed less foliage, grew slower, and needed a longer period to develop, in a dose dependent manner. Most of these larvae died during larval-larval molting, larval-pupal ecdysis or adult emergence. Furthermore, chitin contents in body carcass (without midgut) and integument specimen of the teflubenzuron-fed larvae significantly decreased, whereas the chitin amount in the midgut peritrophic matrix was not affected. In addition, uridine diphosphate-N-acetylglucosamine-pyrophosphorylase gene (LdUAP1), which was mainly responsible for chitin biosynthesis in ectodermally-derived tissues, was suppressed after teflubenzuron ingestion, in contrast to its partner LdUAP2 for chitin formation in the midgut peritrophic matrix. In a word, by inhibition of chitin production in ectodermally-derived tissues, teflubenzuron is an effective benzoylurea insecticide to L. decemlineata larvae. It can be a valuable tool in effective integrated pest management and insecticide resistance management programs against L. decemlineata.
WenChao G, Chao B, Zhian W, et al. J Agric Food Chem. 2018;66(45):11990-11999. doi: 10.1021/acs.jafc.8b03914.
RNA interference (RNAi) has been developed for plant pest control. In this study, hairpin-type double-stranded RNA (dsRNA) targeting the juvenile hormone (JH) acid methyltransferase (JHAMT) gene (dsJHAMT) was introduced in potato plants via Agrobacterium-mediated transformation. The results indicated that the transcriptional RNA of dsJHAMT accumulated in the transgenic plants. The transcripts and proteins of the L. decemlineata JHAMT gene were significantly reduced in larvae feeding on dsJHAMT transgenic foliage. The dsJHAMT had a significant negative effect on the growth and development of L. decemlineata, especially resulting in less oviposition. Importantly, in the field trials, transgenic plants are high-efficiently protected from insect damage mainly because surviving insects laid fewer or no eggs. Even full protection from beetle damage can be acquired by continuously lowering insect population size at large scale in the field over the years. Therefore, the transgenic plants expressing dsJHAMT successfully provided an additional option for plant pest control.
Crossley MS, Rondon SI, Schoville SD. Evolutionary Applications. 2019;12(4):804-814. doi: 10.1111/eva.12757.
Changing landscape heterogeneity can influence connectivity and alter genetic variation in local populations, but there can be a lag between ecological change and evolutionary responses. Temporal lag effects might be acute in agroecosystems, where land cover has changed substantially in the last two centuries. Here, we evaluate how patterns of an insect pest's genetic differentiation are related to past and present agricultural land cover change over a 150-year period. We quantified change in the amount of potato, Solanum tuberosum L., land cover since 1850 using county-level agricultural census reports, obtained allele frequency data from 7,408 single-nucleotide polymorphism loci, and compared effects of historic and contemporary landscape connectivity on genetic differentiation of Colorado potato beetle, Leptinotarsa decemlineata Say, in two agricultural landscapes in the United States. We found that potato land cover peaked in Wisconsin in the early 1900s, followed by rapid decline and spatial concentration, whereas it increased in amount and extent in the Columbia Basin of Oregon and Washington beginning in the 1960s. In both landscapes, we found small effect sizes of landscape resistance on genetic differentiation, but a 20× to 1,000× larger effect of contemporary relative to historic landscape resistances. Demographic analyses suggest population size trajectories were largely consistent among regions and therefore are not likely to have differentially impacted the observed patterns of population structure in each region. Weak landscape genetic associations might instead be related to the coarse resolution of our historical land cover data. Despite rapid changes in agricultural landscapes over the last two centuries, genetic differentiation among L. decemlineata populations appears to reflect ongoing landscape change. The historical landscape genetic framework employed in this study is broadly applicable to other agricultural pests and might reveal general responses of pests to agricultural land-use change.
Pan D, QingYu X, KaiYun F, WenChao G, GuoQing L. Insect Biochem Mol Biol. 2018;103:1-11. doi: 10.1016/j.ibmb.2018.10.001.
It is noted that insect insulin/insulin-like growth factor/target of rapamycin signaling is critical for the regulation of metamorphosis in holometabolous insects. However, the molecular mechanism remains undetermined. Our previous findings reveal that RNA interference (RNAi)-mediated knockdown of an insulin gene (LdILP2) in Leptinotarsa decemlineata disturbs both 20-hydroxyecdysone (20E) and juvenile hormone (JH) signaling, and impairs pupation. In the present paper, we further observed that the expression of the insulin receptor substrate gene chico (Ldchico) and the phosphoinositide-3-kinase gene pi3k (Ldpi3k92E) was repressed in LdILP2 depleted larvae. Moreover, RNAi of Ldchico or Ldpi3k92E decreased food consumption, affected absorption and metabolism of amino acids and sugars, and reduced expression of several 20E (LdEcR, LdHR3 and LdE75) and JH (LdJHAMT, LdKr-h1 and LdHairy) signaling genes. As a result, larval development was postponed and larval growth was inhibited. Intriguingly, knockdown of Ldchico, rather than Ldpi3k92E, impaired larval-pupal and pupal-adult ecdysis, and specifically repressed transcription of another 20E signaling gene LdUSP. Ingestion of 20E rescued the expression of LdEcR, LdHR3 and LdE75, whereas 20E feeding restored neither the decreased LdUSP mRNA level, nor the reduced pupation and adult emergence rates in Ldchico RNAi larvae. Therefore, Chico is critical for the regulation of larval-pupal-adult transition by a PI3K-independent pathway, perhaps through activation of USP in L. decemlineata.
Galimberti A, Alyokhin A. J Econ Entomol. 2018;111(3):1261-1267. doi: 10.1093/jee/toy046.
Mineral oil is a product used to reduce Potato Virus Y transmission in potato fields. However, there is little information available about other effects that oil may have on insect pests of potato. To better understand how mineral oil affects potato pests, we performed a series of experiments testing the effects of oil on mortality, behavior, and development of potato aphids, Macrosiphum euphorbiae (Thomas) (Hemiptera: Aphididae), green peach aphids, Myzus persicae (Sulzer) (Hemiptera: Aphididae), and Colorado potato beetles, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae). All three species showed negative behavioral responses to oil-treated potato foliage. Oil treatment also increased aphid mortality. Colorado potato beetle mortality was not affected, but developing on oil-treated potato plants resulted in prolonged development and smaller adults. Additionally, oil acted synergistically with the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Clavicipitaceae); Colorado potato beetle larvae were killed more rapidly when sprayed with both products compared with when sprayed with B. bassiana alone. Based on these results, mineral oil has the potential for expanded use in potato IPM programs.
Wetzel WC, Aflitto NC, Thaler JS. Ecology. 2018;99(10):2338-2347. doi: 10.1002/ecy.2472.
A growing number of studies have manipulated intraspecific plant diversity and found dramatic changes in the densities of associated insect herbivores and their predators. While these studies have been essential for quantifying the net ecological consequences of intraspecific plant diversity, they have been less effective at uncovering the ways in which plant diversity alters trophic interactions within arthropod communities. We manipulated intraspecific plant diversity and predation risk in the field in a factorial design to reveal how a mixture of plant genotypes changes the response of an herbivorous beetle (Leptinotarsa decemlineata) to a common stink bug predator (Podisus maculiventris). We repeated the manipulations twice across the ontogeny of the beetle to examine how the effects of diversity on the predator-prey interaction differ between larval and adult stages. We found that intraspecific plant diversity, mixtures of susceptible and resistant varieties of potato (Solanum tuberosum), reduced larval survival by 20% and adult oviposition by 34%, which surprisingly put survival and oviposition lower in the mixed-genotype plots than in the resistant monocultures. Moreover, we found that predation risk reduced larval survival 25% and 11% in resistant and susceptible monocultures, respectively, but had no effect in the mixture. This result indicated that our genotypic mixing treatment interacted nonadditively with predation risk such that plant diversity altered the predator-prey interaction by changing the responses of the beetles to their stink bug predators. In addition, even though predation risk reduced larval survival, it increased adult overwintering survival by 9%, independently of plant treatment, suggesting that these interactions change through ontogeny. A key implication of our study is that plant diversity influences arthropod communities not only by changing resource quality, as past studies have suggested, but also by changing interactions between species within the arthropod community.