Chung SH, Scully ED, Peiffer M, et al. Scientific Reports. 2017;7(1):39690. doi: 10.1038/srep39690.

Herbivore associated bacteria are vital mediators of plant and insect interactions. Host plants play an important role in shaping the gut bacterial community of insects. Colorado potato beetles (CPB; Leptinotarsa decemlineata) use several Solanum plants as hosts in their natural environment. We previously showed that symbiotic gut bacteria from CPB larvae suppressed jasmonate (JA)-induced defenses in tomato. However, little is known about how changes in the bacterial community may be involved in the manipulation of induced defenses in wild and cultivated Solanum plants of CPB. Here, we examined suppression of JA-mediated defense in wild and cultivated hosts of CPB by chemical elicitors and their symbiotic bacteria. Furthermore, we investigated associations between the gut bacterial community and suppression of plant defenses using 16 S rRNA amplicon sequencing. Symbiotic bacteria decreased plant defenses in all Solanum hosts and there were different gut bacterial communities in CPB fed on different host plants. When larvae were reared on different hosts, defense suppression differed among host plants. These results demonstrate that host plants influence herbivore gut bacterial communities and consequently affect the herbivore's ability to manipulate JA-mediated plant defenses. Thus, the presence of symbiotic bacteria that suppress plant defenses might help CPB adapt to host plants.

Weintraub R, Garrido E, Poveda K. American Journal of Potato Research. 2018;95(6):642-649. doi: 10.1007/s12230-018-9670-0.

Tolerance is a type of defense that allows plants to attenuate the negative effects of herbivory. Tolerance has been shown to be context-dependent, contingent on abiotic and biotic factors such as nutrients and plant age. Here, we determine the simultaneous effect of herbivory at different phenological stages and nitrogen regimen on the potato's ability to tolerate herbivory. We subjected young and blooming plants of two potato varieties to 50% injury by Colorado Potato Beetle in low and high nitrogen environments to determine their effects on tuber yield and plant tolerance. All plants in the high nitrogen treatment expressed higher yield and tolerance compared to those in the low nitrogen treatment. Control plants expressed higher yield than plants in either herbivory treatment. There was a variety by phenological stage of herbivory interaction showing that phenological-based tolerance expression within species is genotype dependent.

López-Galiano MJ, Ruiz-Arroyo V, Fernández-Crespo E, et al. J Plant Physiol. 2017;215:59-64. doi: 10.1016/j.jplph.2017.04.013.

Insect-plant interactions are governed by a complex equilibrium between the mechanisms through which plant recognize insect attack and orchestrate downstream signaling events that trigger plant defense responses, and the mechanisms by which insects overcome plant defenses. Due to this tight and dynamic interplay, insight into the nature of the plant defense response can be gained by analyzing changes in the insect herbivores digestive system upon plant feeding. In this work we have identified a Solanum melongena miraculin-like protease inhibitor in the midgut juice of Colorado potato larvae feeding on eggplant plants treated with the natural inducer of plant defenses hexanoic acid. We analyzed the corresponding gene expression by qRT-PCR and our results showed that this eggplant miraculin-like gene enhanced induction contributes to the hexanoic acid priming effect in this Solanaceae species. Moreover, our data evidencing that OPDA might be involved in this gene regulation highlights its potential as biomarker in eggplant plant responses to stress mediated this oxylipin signaling pathway.

Wetzel WC, Thaler JS. Oecologia. 2018;186(2):483-493. doi: 10.1007/s00442-017-4034-x.

A consequence of plant diversity is that it can allow or force herbivores to consume multiple plant species, which studies indicate can have major effects on herbivore fitness. An underappreciated but potentially important factor modulating the consequences of multi-species diets is the extent to which herbivores can choose their diets versus being forced to consume specific host-plant sequences. We examined how host-selection behavior alters the effects of multi-species diets using the Colorado potato beetle (Leptinotarsa decemlineata) and diets of potato plants (Solanum tuberosum), tomato plants (S. lycopersicum), or both. When we gave beetles simultaneous access to both plants, allowing them to choose their diets, their final mass was within 0.1% of the average mass across both monocultures and 43.6% lower than mass on potato, the superior host in monoculture. This result indicates these beetles do not benefit from a mixed diet, and that the presence of tomato, an inferior but suitable host, makes it difficult to use potato. In contrast, when we forced beetles to switch between host species, their final mass was 37.8% less than the average of beetles fed constant diets of either host species and within 3.5% of the mass on tomato even though they also fed on potato. This indicates preventing host-selection behavior magnified the negative effects of this multi-species diet. Our results imply that ecological contexts that constrain host-selection or force host-switches, such as communities with competition or predation, will lead plant species diversity to reduce the performance of insect herbivores.

Tryjanowski P, Sparks TH, Blecharczyk A, Małecka-Jankowiak I, Switek S, Sawinska Z. American Journal of Potato Research. 2018;95(1):26-32. doi: 10.1007/s12230-017-9611-3.

Potato Solanum tuberosum is one of the world's four most important crops. Its cultivation is steadily increasing in response to the need to feed a growing world population. The yield of potato is influenced inter alia by both climate and pests. The main defoliator pest of potato is Colorado potato beetle Leptinotarsa decemlineata. Using data from a long-term experiment (1958-2013) in western Poland, we show that increasing temperature has affected the trophic relationship between potato and Colorado potato beetle. The planting, leafing, flowering and harvest dates for potato were advanced, after controlling for different cultivars, by 2.00 days, 3.04 days, 3.80 days and 3.42 days respectively for every 1°C increase in temperature. In contrast, first treatment against Colorado potato beetle advanced by 4.66 days for every 1°C increase in temperature, and, furthermore, the number of treatments against the beetle increased by 0.204 per 1°C increase in temperature. This suggests that the beetle responds faster to increasing temperature than the plant does, but both parts of the system are probably greatly modified by farming practices.

Bozov PI, Georgieva YP. Natural Product Communications. 2017;12(3):327-328.

Fourteen neo-clerodane diterpenoids isolated from Scutellaria altissima (Lamiaceae) were tested for insect antifeedant activity against Leptinotarsa decemlineata Say. Potato leaf disks treated with small amounts of the compounds (concentration 1000, 100, 10 ppm) resulted in good to very good antifeedant activity. Clerodin (1), scutecyprin (11) and 11-epi-scutecolumnin C (12) showed strong feeding inhibition at 1000 ppm and exhibited significant antifeedant activity at a concentration of 100 ppm. Activity was established by calculating the feeding ratio (FR) between the consumed areas of treated disks (CTD) and control disks (CCD). For comparison, FR50 values were determined as the FR at a CCD of 50%. Structural features of the compounds associated with the changes in activity and structure-antifeedant activity relationships are discussed. For the first time the anti-feedant activity has been evaluated of neo-clerodane diterpenoids with an unusual R-configuration of the carbon atom C-11.

Crossley MS, Pélissié B, Cohen Z, Schoville SD. Great Lakes Entomol. 2017;50(3):93-97.

Egg, larval, and adult life stages of Colorado potato beetle, Leptinotarsa decemlineata (Say), were observed feeding on or attached to a previously undocumented host plant belonging to the genus Chamaesaracha in eastern Colorado on July 2017. At one site, L. decemlineata were more abundant on Chamaesaracha sp. than the accepted ancestral host plant, Solanum rostratum (Dunal). While future studies should confirm the ancestral status of the observed L. decemlineata and suitability of Chamaesaracha sp. for completion of development, our observations suggest a need for further characterization of the ancestral host range of L. decemlineata.

Kalsi, M. and S. R. Palli. 2017. Insect Biochemistry and Molecular Biology 83: 1-12.

Colorado potato beetle (CPB), Leptinotarsa decemlineata is a notorious pest of potato. Co-evolution with Solanaceae plants containing high levels of toxins (glycoalkaloids) helped this insect to develop an efficient detoxification system and resist almost every chemical insecticide introduced for its control. Even though the cross-resistance between plant allelochemicals and insecticides is well acknowledged, the underlying molecular mechanisms are not understood. Here, we investigated the molecular mechanisms involved in detoxification of potato plant allelochemicals and imidacloprid resistance in the field-collected CPB. Our results showed that the imidacloprid-resistant beetles employ metabolic detoxification of both potato plant allelochemicals and imidacloprid by upregulation of common cytochrome P450 genes. RNAi aided knockdown identified four cytochromes P450 genes (CYP6BJa/b, CYP6BJ1v1, CYP9Z25, and CYP9Z29) that are required for defense against both natural and synthetic chemicals. These P450 genes are regulated by the xenobiotic transcription factors Cap n Collar C, CncC and muscle aponeurosis fibromatosis, Maf. Studies on the CYP9Z25 promoter using the luciferase reporter assay identified two binding sites (i.e. GCAGAAT and GTACTGA) for CncC and Maf. Overall, these data showed that CPB employs the metabolic resistance mediated through xenobiotic transcription factors CncC and Maf to regulate multiple P450 genes and detoxify both imidacloprid and potato plant allelochemicals.

Skuhrovec, J., Douda, O., Pavela, R. et al. Am. J. Potato Res. (2016). doi:10.1007/s12230-016-9549-x

The effect of essential oil (EO) from anise (Pimpinellia anisum) on the mortality of young larvae of Colorado potato beetles has been studied. In our bioassays, P. anisum EO significantly increased the mortality of the second instar larvae of L. decemlineata. Significantly different values of LD50 and LD90 were established for acute (LD50 = 1.76, and LD90 = 8.29) as well as chronic toxicity (LD50 = 0.45, and LD90 = 1.01). Decrease of both values over experimental period was evident, which showed that the larval mortality was slow and cumulative. The composition of EO used for biological experiments was also assessed. The main component detected in EO from P. anisum was anethole (79.87%), followed by anisaldehyde (7.74%), estragole (5.88%) and β-linalool (1.07%). Within five days, residual concentration of EO decreased from 3.87 mg/g of dry weight immediately after foliar applications to 0.9 mg per g of dry weight. The effect of this slow evaporation could be explained by dominant presence of anethole or by the type of formulation and the addition of oil and tween. Results of our study demonstrate that EO from P. anisum has insecticidal properties that may lead to the development of new organic products for the control of Colorado potato beetles.