Leaf Induction Impacts Behavior and Performance of a Pollinating Herbivore

Flowering plants use volatiles to attract pollinators while deterring herbivores. Vegetative and floral traits may interact to affect insect behavior. Pollinator behavior is most likely influenced by leaf traits when larval stages interact with plants in different ways than adult stages, such as when larvae are leaf herbivores but adult moths visit flowers as pollinators. Here, we determine how leaf induction and corresponding volatile differences in induced plants influence behavior in adult moths and whether these preferences align with larval performance. We manipulated vegetative induction in four Nicotiana species. Using paired induced and control plants of the same species with standardized artificial flowers, we measured foraging and oviposition choices by their ecologically and economically important herbivore/pollinator, Manduca sexta. In parallel, we measured growth rates of M. sexta larvae fed leaves from control or induced plants to determine if this was consistent with female oviposition preference. Lastly, we used plant headspace collections and gas chromatography to quantify volatile compounds from both induced and control leaves to link changes in plant chemistry with moth behavior. In the absence of floral chemical cues, vegetative defensive status influenced adult moth foraging preference from artificial flowers in one species (N. excelsior), where females nectared from induced plants more often than control plants. Plant vegetative resistance consistently influenced oviposition choice such that moths deposited more eggs on control plants than on induced plants of all four species. This oviposition preference for control plants aligned with higher larval growth rates on control leaves compared with induced leaves. Control and induced plants of each species had similar leaf volatile profiles, but induced plants had higher emission levels. Leaves of N. excelsior produced the most volatile compounds, including some inducible compounds typically associated with floral scent. We demonstrate that vegetative plant defensive volatiles play a role in host plant selection and that insects assess information from leaves differently when choosing between nectaring and oviposition locations. These results underscore the complex interactions between plants, their pollinators, and herbivores.

Phylogeny, taxonomy and flower-breeding ecology of the Colocasiomyia cristata species group (Diptera: Drosophilidae), with descriptions of ten new species

The phylogeny of the Colocasiomyia cristata species group is reconstructed as a hypothesis, based on DNA sequences of two mitochondrial and six nuclear genes and 51 morphological characters. The resulting tree splits this species group into two clades, one of which corresponds to the colocasiae subgroup. Therefore, a new species subgroup named as the cristata subgroup is established for the other clade. Within the cristata subgroup, three subclades are recognized and each of them is defined as a species complex: the cristata complex composed of five species (including three new ones: C. kinabaluana sp. nov., C. kotana sp. nov. and C. matthewsi sp. nov.), the sabahana complex of two species (C. sabahana sp. nov. and C. sarawakana sp. nov.), and the xenalocasiae complex of five species (including C. sumatrana sp. nov. and C. leucocasiae sp. nov.). There are, however, three new species (C. ecornuta sp. nov., C. grandis sp. nov. and C. vieti sp. nov.) not assigned to any species complex. In addition, breeding habits are described for four cristata-subgroup species, each of which monopolizes its specific host plant. And, data of host-plant use are compiled for all species of the cristata group from records at various localities in the Oriental and Papuan regions. The evolution of host-plant selection and sharing modes is considered by mapping host-plant genera of each species on the phylogenetic tree resulting from the present study.

Maize root-associated microbes likely under adaptive selection by the host to enhance phenotypic performance

The root-associated microbiome (rhizobiome) plays a non-negligible role in determining plant health, stress tolerance, and nutrient use efficiency. However, it remains unclear to what extent the composition of the rhizobiome is governed by intraspecific variation in host plant genetics in the field and the degree to which host plant selection can reshape the composition of the rhizobiome. Here we quantify the rhizosphere microbial communities associated with a replicated diversity panel of 230 maize (Zea mays L.) genotypes grown in agronomically relevant conditions under high N (+N) and low N (-N) treatments. We show that the abundance of many root-associated microbes within a functional core microbial community of 150 abundant and consistently reproducible microbial groups is explainable by natural genetic variation in the host plant, with a greater proportion of microbial variance attributable to plant genetic variation in low N conditions. Population genetic approaches identify signatures of purifying selection in the maize genome associated with the abundance of several groups of microbes in the maize rhizobiome. Genome-wide association studies conducted using rhizobiome phenotypes identified n = 467 microbe-associated plant loci (MAPLs) in the maize genome linked to variation in the abundance of n = 115 microbial groups in the maize rhizosphere. In 62/115 cases, which is more than expected by chance, the abundance of these same microbial groups was correlated with variation in plant vigor indicators derived from high throughput phenotyping of the same field experiment. This study provides insights into harnessing the full potential of root-associated microbial symbionts in maize production.

Environmentally acquired chemical camouflage affects Pieris brassicae L. host plant selection and orientation behaviour of a larval parasitoid

Environmentally acquired chemical camouflage is a phenomenon, where a plant growing close to a strong volatile organic compound (VOC) emitter will adsorb and re-emit the VOCs produced by the neighbouring plant. The re-emitted volatile bouquet may resemble more the VOC composition of the neighbour than plant’s own typical odour, and thus act as chemical camouflage against insect detection, potentially simultaneously providing associational resistance towards herbivory. We exposed a pest-sensitive horticultural crop, Brassica oleracea var. italica (broccoli) cv. Lucky, to the volatiles emitted by Rhododendron tomentosum [RT] twigs and assessed the host selection by ovipositing females and larval instars of the major caterpillar pest Pieris brassicae between RT-exposed and control plants. Potential impact of RT exposure on herbivore natural enemies was studied using behavioural tests with a parasitoid wasp Cotesia glomerata. P. brassicae females laid significantly less eggs and egg clusters were fewer on RT-exposed plants at both night-time (6 °C) and daytime (22 °C) temperatures. Larvae preferred leaves from control plants over RT-exposed plants at both temperatures. Preceding RT-exposure did not disturb orientation of parasitoid wasp Cotesia glomerata females towards B. oleracea plants damaged by its host P. brassicae. However, host-damaged control plants were favoured by the parasitoid over RT-exposed, host-damaged plants. Our results suggest that companion plant based chemical camouflage as a mechanism of pest suppression could be developed as an additional tool for the integrated pest management toolbox in agriculture.

Whitefly Network Analysis Reveals Gene Modules Involved in Host Plant Selection, Development and Evolution

Whiteflies are Hemipterans that typically feed on the undersides of plant leaves. They cause severe damage by direct feeding as well as transmitting plant viruses to a wide range of plants. However, it remains largely unknown which genes play a key role in development and host selection. In this study, weighted gene co-expression network analysis was applied to construct gene co-expression networks in whitefly. Nineteen gene co-expression modules were detected from 15560 expressed genes of whitefly. Combined with the transcriptome data of salivary glands and midgut, we identified three gene co-expression modules related to host plant selection. These three modules contain genes related to host-plant recognition, such as detoxification genes, chemosensory genes and some salivary gland-associated genes. Results of Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses elucidated the following pathways involved in these modules: lysosome, metabolic and detoxification pathways. The modules related to the development contain two co-expression modules; moreover, the genes were annotated to the development of chitin-based cuticle. This analysis provides a basis for future functional analysis of genes involved in host-plant recognition.

Plant chemicals affect trade-offs between adult preference and larval performance of the rice water weevil, Lissorhoptrus oryzophilus

Herbivores use plant chemicals for host-plant selection to maximize their own and/or offspring performance. Since host plants that are optimal for mother and offspring are often different and spatially/temporally separated, how plant chemicals affect trade-offs between adult preference and larval performance remains unclear. We found that adults of the rice water weevil (Lissorhoptrus oryzophilus), one of the most important pests on rice in the world, preferred volatiles from barnyard grass over rice, tended to feed and oviposit on barnyard grass compared with rice. In contrast, larvae performed better on rice roots than on barnyard grass roots. Chemical analysis further show that rice roots had higher nitrogen and soluble sugar but lower lignin and cellhouse contents than barnyard grass. Together, these results suggest that violate, nutritive and defensive chemicals could jointly determine trade-offs of the adult preference and larval performance on these two hosts. As developing chemical-based technology is one of the main approaches for control of pest insects, our findings may also contribute to the future efforts for management of the rice water weevil.

Root-associated entomopathogenic fungi manipulate host plants to attract herbivorous insects

Root-associated entomopathogenic fungi (R-AEF) indirectly influence herbivorous insect performance. However, host plant-R-AEF interactions and R-AEF as biological control agents have been studied independently and without much attention to the potential synergy between these functional traits. In this study, we evaluated behavioral responses of cabbage root flies [Delia radicum L. (Diptera: Anthomyiidae)] to a host plant (white cabbage cabbage Brassica oleracea var. capitata f. alba cv. Castello L.) with and without the R-AEF Metarhizium brunneum (Petch). We performed experiments on leaf reflectance, phytohormonal composition and host plant location behavior (behavioral processes that contribute to locating and selecting an adequate host plant in the environment). Compared to control host plants, R-AEF inoculation caused, on one hand, a decrease in reflectance of host plant leaves in the near-infrared portion of the radiometric spectrum and, on the other, an increase in the production of jasmonic, (+)-7-iso-jasmonoyl-l-isoleucine and salicylic acid in certain parts of the host plant. Under both greenhouse and field settings, landing and oviposition by cabbage root fly females were positively affected by R-AEF inoculation of host plants. The fungal-induced change in leaf reflectance may have altered visual cues used by the cabbage root flies in their host plant selection. This is the first study providing evidence for the hypothesis that R-AEF manipulate the suitability of their host plant to attract herbivorous insects.