Reciprocal interactions between aphids and arbuscular mycorrhizal fungi across plant generations

The conditions experienced by one plant generation can influence the growth of the offspring generation. These maternal effects can reduce performance of foliar-feeding insects, through accumulation of plant defences. Arbuscular mycorrhizal fungi (AMF) inhabit the roots of plants and are known to influence the performance of foliar-feeding insects. However, all published studies of the interactions between insects and AMF have taken place within one plant generation, but none across generations. Thus, in the present study, Senecio vulgaris plants were grown with or without aphids and AMF (termed ‘induction events’), and seeds from each treatment were used to grow plants experiencing that same treatment over four successive generations, all grown in identical environmental conditions. Naïve aphids were reared on Senecio plants whose parents had experienced 0, 1, 2 or 3 induction events. We found strong negative maternal effects of herbivory on aphid growth, which were not mitigated by the mycorrhiza. However, teneral weight and growth rate showed a gradual recovery; aphids reared on plants whose previous three generations suffered attack were similar in size to those at the beginning of the study. Herbivory had positive or negative effects on the mycorrhiza, dependent upon the number of previous generations suffering attack or having mycorrhizal associations. We conclude that the outcome of many insect plant fungal experiments is likely to have been influenced by and need to account for maternal effects of the parental plant’s growth conditions.

The effect of landscape on Cucurbita pepo-pollinator interaction networks varies depending on plants’ genetic diversity

In recent years, evidence has been found that plant-pollinator interactions are altered by land-use and that genetic diversity also plays a role. However, how land-use and genetic diversity influence plant–pollinator interactions, particularly in the Neotropics, where many endemic plants exist is still an open question. Cucurbita pepo is a monoecious plant and traditional crop wide distributed, with high rates of molecular evolution, landraces associated with human cultural management and a history of coevolution with bees, which makes this species a promising model for studying the effect of landscape and genetic diversity on plant-pollinator interactions. Here, we assess (1) whether female and male flowers differences have an effect on the interaction network, (2) how C. pepo genetic diversity affects flower-bee visitation network structure, and (3) what is the effect that land-use, accounting for C. pepo genetic variability, has on pumpkin-bee interaction network structure. Our results indicate that female and male flowers presented the same pollinator community composition and interaction network structure suggesting that female/male differences do not have a significant effect on network evolution. Genetic diversity has a positive effect on modularity, nestedness and number of interactions. Further, the effect of semi-natural areas on nestedness could be buffered when genetic diversity is high. Our results suggest that considering genetic diversity is relevant for a better understanding of the effect of land-use on interaction networks. Additionally, this understanding has great value in conserving biodiversity and enhancing the stability of interaction networks in a world facing great challenges of habitat and diversity loss.

Irrigated trap crops impact key hemipteran pests in organic pistachio orchard

Using sown groundcovers as trap crops to protect a cash crop is a traditional pest management tool. Pistachio is a major crop in California’s Central Valley, where high summer temperatures and little to no precipitation between May and November lead to summer dry-down of annual groundcover. Hemipteran pests that consist of ‘small bugs’ and ‘large bugs’ are a major contributor to nut damage, especially in organic production. In this 2-year field study, we tested the use of irrigated trap crop mixtures, sown between tree rows, to reduce those hemipteran pests’ abundance or damage. Biweekly beat samples of the tree canopy and sweep samples of the sown groundcovers in trap crop plots and resident weedy vegetation in control plots were taken over two consecutive growing seasons. Arthropod richness and abundance were highest in the groundcover and tree canopy in the trap crop plots. Small and large bug pest populations were higher and lower, respectively, in the tree canopy in trap crop plots, indicating a mixed response of these hemipterans to the presence of the trap crops. Additionally, natural enemy populations were more abundant in the tree canopy in trap crop plots than in control plots. There was no difference in nut damage between plots with and without the trap crop. These findings suggest that populations of hemipteran pests and beneficials can be manipulated successfully with irrigated trap crops, but future studies will need to focus on doing so in a way that decreases hemipteran pistachio damage.