Nguyen D, Poeschl Y, Lortzing T, et al. International Journal of Molecular Sciences. 2018;19(12):3845.
In nature, plants are frequently subjected to multiple biotic and abiotic stresses, resulting in a convergence of adaptive responses. We hypothesised that hormonal signalling regulating defences to different herbivores may interact with drought responses, causing distinct resistance phenotypes. To test this, we studied the hormonal and transcriptomic responses of Solanum dulcamara subjected to drought and herbivory by the generalist Spodoptera exigua (beet armyworm; BAW) or the specialist Leptinotarsa decemlineata (Colorado potato beetle; CPB). Bioassays showed that the performance of BAW, but not CPB, decreased on plants under drought compared to controls. While drought did not alter BAW-induced hormonal responses, it enhanced the CPB-induced accumulation of jasmonic acid and salicylic acid (SA), and suppressed ethylene (ET) emission. Microarray analyses showed that under drought, BAW herbivory enhanced several herbivore-induced responses, including cell-wall remodelling and the metabolism of carbohydrates, lipids, and secondary metabolites. In contrast, CPB herbivory enhanced several photosynthesis-related and pathogen responses in drought-stressed plants. This may divert resources away from defence production and increase leaf nutritive value. In conclusion, while BAW suffers from the drought-enhanced defences, CPB may benefit from the effects of enhanced SA and reduced ET signalling. This suggests that the fine-tuned interaction between the plant and its specialist herbivore is sustained under drought.
Crossley MS, Schoville SD, Haagenson DM, Jansky SH. J Econ Entomol. 2018;111(4):1875-1884. doi: 10.1093/jee/toy120.
Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), is a serious global pest of potato, Solanum tuberosum L. Management of L. decemlineata has relied heavily on insecticides, but repeated evolution of insecticide resistance has motivated the exploration and development of alternative strategies, such as plant resistance. The recent development of two diploid potato families derived from crosses between cultivated and wild potato species (S. chacoense and S. berthaultii) has provided a unique opportunity to reexamine plant traits for resistance breeding. In this 2-yr study, we surveyed select F2 clones for the induction of L. decemlineata mortality and a reduction in defoliation in no-choice feeding assays when challenged with adults and larvae from three sites in Wisconsin. We tested for an association with glandular trichome density and foliar levels of the glycoalkaloids chaconine and solanine. Several potato clones demonstrated resistance in specific feeding assays, but none excelled consistently across experiments. Mortality and defoliation generally differed significantly among L. decemlineata populations, which could be indicative of heritable variation in beetle responses to plant defenses or variation in the physiological status of the beetle populations tested. Contrary to expectations, higher trichome density increased mortality or decreased defoliation in only a few cases, and levels of mortality and defoliation were unrelated to foliar glycoalkaloid content, warranting further investigation of the defense mechanisms of resistant clones. In addition to identifying several potential L. decemlineata resistance sources, this study underscores the need to include multiple insect populations in surveys of plant resistance to this diverse pest.
Cingel A, Savić J, Lazarević J, et al. Insect Science. 2017;24(5):768-780. doi: 10.1111/1744-7917.12364.
Colorado potato beetle (CPB; Leptinotarsa decemlineata Say, Coleoptera: Chrysomelidae) has shown a remarkable adaptability to a variety of control measures. Although oryzacystatin I and II (OCI and OCII) have potential in controlling pests that use cysteine proteinases for food digestion, expression of a single OC gene in potato exhibited a minimal or no effect on CPB fitness traits. The aim of this study was to examine the effect of coexpressed OCI and OCII in potato (Solanum tuberosum L.) cultivars Desiree, Dragačevka and Jelica on CPB larvae. Growth parameters, consumption rates and food utilization, as well as activity of proteases of CPB larvae were assayed. Second and third instar larvae fed on transformed leaves molted earlier and had higher relative growth and consumption rates than larvae fed on nontransformed leaves, while efficiency of food utilization was unaffected. In contrast, fourth instar maximum weight gain and amount of leaves consumed were about 20% lower for the larvae fed on transgenic potato. Analysis of total protease activity of third instar larvae revealed reduction in overall proteolytic activity measured by azocasein hydrolysis, accompanied with inhibition of cysteine proteinase activity 24 h after ingestion of potato leaves expressing OCI and OCII. However, after long-term feeding on transformed leaves proteolytic activities of larvae became similar to the controls. Although feeding on OCI/OCII leaves did not affect larval survival, coexpression of OC genes reduced the development time and thus significantly decreased plant damage caused by CPB larvae.
Izzo VM, Chen YH, Schoville SD, Cong W, Hawthorne DJ. J Econ Entomol. 2018;111(2):868-878. doi: 10.1093/jee/tox367.
Colorado potato beetle (Leptinotarsa decemlineata Say [Coleoptera: Chrysomelidae]) is a pest of potato throughout the Northern Hemisphere, but little is known about the beetle's origins as a pest. We sampled the beetle from uncultivated Solanum host plants in Mexico, and from pest and non-pest populations in the United States and used mitochondrial DNA and nuclear loci to examine three hypotheses on the origin of the pest lineages: (1) the pest beetles originated from Mexican populations, (2) they descended from hybridization between previously divergent populations, or (3) they descended from populations that are native to the Plains states in the United States. Mitochondrial haplotypes of non-pest populations from Mexico and Arizona differed substantially from beetles collected from the southern plains and potato fields in the United States, indicating that beetles from Mexico and Arizona did not contribute to founding the pest lineages. Similar results were observed for AFLP and microsatellite data. In contrast, non-pest populations from the states of Colorado, Kansas, Nebraska, New Mexico, and Texas were genetically similar to U.S. pest populations, indicating that they contributed to the founding of the pest lineages. Most of the pest populations do not show a significant reduction in genetic diversity compared to the plains populations in the United States. We conclude that genetically heterogeneous beetle populations expanded onto potato from native Solanum hosts. This mode of host range expansion may have contributed to the abundant genetic diversity of contemporary populations, perhaps contributing to the rapid evolution of climate tolerance, host range, and insecticide resistance.
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.