Middleton, E.G. and I. V. MacRae. 2021. Biological Control 152: 104463, https://doi.org/10.1016/j.biocontrol.2020.104463
Wildflower plantings in agroecosystems can support arthropod predators, and may have the potential to increase conservation biological control of pest species in nearby crops. Colorado potato beetle (CPB) is a significant defoliator of potato that is resistant to many forms of management. Promoting natural enemies of CPB by establishing perennial wildflower plantings in field margins may provide a measure of control for this pest. We examined the impacts of floral plantings on the abundance of known CPB predators, predation of CPB egg masses, and CPB populations in a commercial agroecosystem. Floral plantings increased the abundance of CPB predators, but did not significantly increase the rate of predation of sentinel CPB egg masses within field margins. Within nearby potato fields, predator abundance and predation rates on CPB eggs were unaffected by the presence of flowers. Colorado potato beetle abundance in potato fields was also not impacted by floral plantings. However, floral margins may provide improved overwintering opportunities for CPB, and further investigation is needed. Perennial wildflower plantings show potential for attracting predators that prey on CPB, but these benefits do not extend into nearby potato crops.
Miller T, Crossley MS, Fu Z, Meier AR, Crowder DW, Snyder WE. 2020. Biological Control. 151:104403.
Prey commonly must compete with conspecifics for resources while also defending themselves against predators. Both competition and defense can reduce feeding opportunities, or otherwise strain prey energy reserves, even when the prey is not killed. This suggests that stress from competition and anti-predator defense might yield non-lethal harm that differs quantitatively rather than qualitatively. We examined this possibility for an herbivorous prey species, the Colorado potato beetle (Leptinotarsa decemlineata), feeding among differing numbers of intraspecific competitors while also avoiding predation by Nabis alternatus and Hippodamia convergens. In a field cage experiment, predators and intraspecific competitors similarly reduced the herbivores’ larval survival. Yet, only exposure to predators heightened the risk of beetles later being killed by entomopathogenic nematodes and fungi, as the beetles pupated in the soil. This suggests that the threat of predation was exerting physiological harm to the prey, although it was also possible that a tradeoff existed where those beetles most resistant to predator attack were most susceptible to pathogen infection. In a second experiment, we found that regular touching of larvae by predatory Nabis or Hippodamia, in the absence of actual predation, consistently induced predator-avoidance behaviors by the larvae (e.g., rearing, vomiting, wiggling, etc.) that might be energetically costly. Indeed, only being touched by predators, but not by a wooden dowel as a disturbance control, led to greater susceptibility to entomopathogens as pupae. Altogether, our findings suggest that non-lethal interactions with predators might carry a particular cost to beetles in heightened pathogen susceptibility, not seen when facing competitors or simple disturbance. Additional work is needed to determine the specific physiological mechanism underlying this apparent synergism in the effects of predators and entomopathogens, which spans prey life stages.
Kang W-N, Fu K-Y, Guo W-C, Li G-Q. 2020. Microbiology Resource Announcements. 9(25).
Bacteria of the genus Stenotrophomonas are opportunistic and have been documented in the guts of several insect species. Here, we present the complete genome sequence of S. maltophilia strain CPBW01, isolated from the wings of the Colorado potato beetle, Leptinotarsa decemlineata, collected from potato fields in Urumqi (43.71N, 87.39E), Xinjiang, China.
Aflitto NC, Thaler JS. 2020. Ecological Entomology. 45(5):1190–1199.
The influence of predator cues on the behaviour of prey is well supported in the literature; however, a clear understanding of how predator cues affect prey in variable environmental conditions and over longer time scales is needed to better understand the underlying mechanisms. Here, we measure how predator odors affect herbivore colonization, abundance, oviposition, and plant damage across two growing seasons. The study system consisted of Leptinotarsa decemlineata (Colorado potato beetle) as prey, and the aggregation pheromone of live Podisus maculiventris (spined soldier bug) as the predator cue in a potato field. In 2016, the amount of feeding damage by early beetle colonists was lower in predator odor-treated plots, reducing plant damage by 22%. Larval abundance was also reduced in treated plots in 2016. Beetle abundance and damage in 2017 was similar in the treatment and control plots. Two mechanisms were investigated to better understand why prey response to the predator odor treatment weakened over the first season, including changes in predator odor cue strength and prey habituation. Predator odor cue strength emerged as a likely explanation, as dispensers, which released a synthetic predator pheromone over the entire season, reduced the probability of finding damage more consistently than the live predator treatment. These results suggest that temporal patterns of predator cue release and strength may drive prey response across the season, underscoring the importance of cue release-rate and consistency in both species interactions and for the future application of modifying insect behaviour using non-consumptive effects in agricultural systems.
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.
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.
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.
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.
Wetzel WC, Aflitto NC, Thaler JS. 2018. Ecology. 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.
Boiteau G, MacKinley P. Can Entomol. 2017;149(2):174-190. doi: 10.4039/tce.2016.52.
This laboratory study confirmed that the strategy of adult terrestrial Colorado potato beetle (Leptinotarsa decemlineata (Say); Coleoptera Chrysomelidae) to survive the threat of drowning in water is based on avoidance of water crossings. It also showed that beetles at the surface of a body of water after failing to avoid it, long considered limited to passive floating and phoretic transport were in fact likely to rely on a complex fight or flee response. Beetles showed capacity to swim in a pattern similar to land foraging beetles. Beetles also tolerated submergence and walked underwater. These active behaviours should improve their probability of finding shore or refuge for longer survival. Results confirmed that Colorado potato beetles are likely to accumulate near water features in the potato agro-ecosystem landscape but suggest that successful crossings and colonisation of crops on the other side are more likely than previously expected. On a larger scale, new information provided by this study combined with our knowledge of dominant winds and currents should make it possible for future research to better predict the probability of surviving encounters with water and the orientation of invasive Colorado potato beetle colonisers dispersing at the surface of bodies of water.