Mattias C. Larsson

Several polyphagous moths are severe crop pests. Diet breadth patterns and mechanisms among polyphagous insects provide an excellent system to study ecological and evolutionary processes in herbivores, driving dietary specialization. However, studies of diet breadth on more than a handful of crops are scarce. Here, we estimated the diet breadth in two species of lepidopteran herbivores from the genus Spodoptera : S. littoralis (SL), with host range including both mono- and dicotyledonous plants and S. frugiperda (SF) Corn strain, primarily adapted to different grass species. Larval performance on 23 crop and wild plant species from 17 families from terrestrial and wetland habitats was compared to an artificial diet in no-choice feeding bioassays. SL survived and performed better on most tested plants, particularly on the family level, except on two monocot plants (maize and leek), where SF performed well. There were five wild non-host plants where both generalists failed to survive. Nutrition indices assay corroborates the findings on a subset of plants. In a subset of plants, larval feeding preference correlated partly, and larval attraction correlated well with larval performance. Female oviposition choice showed a weak correlation with larval performance. This weak correlation implies that these traits are decoupled, and other factors are crucial for female host plant selection. During larval dispersal greenhouse experiments, SL and SF larvae strongly tended to migrate onto their suitable host plants, indicating that this is one factor that modulates female host plant selection. In summary, SL has a broader diet breath compared to SF, surviving on wild plants with no previous exposure. The present study provides the first comprehensive data on the diet breadth of two range-expanding and highly invasive polyphagous herbivores.

Yield loss caused by insect pests remains a substantial problem in agriculture. Chemical control, with potential negative effects on non-target organisms, is still the main tool for pest management. For pest species with limited dispersal capacity, rotation of the crop in time and space has potential as an alternative management measure. This is particularly important in organic farming, where most agrochemicals are prohibited, but also relevant as a complementary pest management strategy in conventional agriculture. Clover is an important crop used for animal feed and as green manure; however, seed-eating weevils can severely limit the seed yield. We hypothesized that the previous year’s clover seed fields constitute the major sources of weevil pests. Consequently, a greater distance to, and a smaller pest load from, this source should reduce the number of weevils colonizing the new seed fields. To map population dynamics and dispersal range ofProtapion fulvipes,an economically important seed weevil specialized on white clover, we conducted field studies over four years in 45 white clover seed fields. We found thatP. fulvipesoverwinters close to its source field and disperses to new fields in early spring the following year. Pest abundance increased with pest load in the previous year’s seed field, but decreased by 68% per km distance to the previous year’s field. Thus, separation of seed production fields between years by 2–3 km would create a spatiotemporal pest management tool to reduce the pest infestation below the estimated economic injury level.

Even though floral scent is of major importance for pollinator attraction, it is less investigated than other floral traits. Previous studies suggest the importance of joint exploration of olfactory and visual floral cues to understand plant–pollinator interactions. We investigated flower scents in Collinsia heterophylla , a bee‐pollinated, annual herb a with mixed‐mating system combining self‐ and outcross‐pollination. In Collinsia , floral size and development variation is related to mating system, ranging from large‐flowered mixed‐mating species to small‐flowered self‐pollinated species. However, to our knowledge, flower scent has not been described in any species in the genus. We also studied whether flower‐emitted volatiles were coupled to presence versus absence of a coloured band on the upper lip within a population in C. heterophylla , and if these colour morphs affected pollinator visitation. We performed headspace collections of volatiles in the greenhouse from potted flowering plants, and compared these to controls in the bud stage. Flower‐specific volatiles were highly dominated by terpenoid compounds typical of bee‐pollinated plants, such as β‐myrcene, ( Z )‐ and ( E )‐ocimene and sesquiterpenes ( E )‐α‐bergamotene and β‐sesquiphellandrene. The aliphatic ester methyl hexanoate was also prominent, together with additional esters, whereas methyl cinnamate constituted the only aromatic compound. Floral colour morphs showed no qualitative difference in volatiles, but the coloured morph produced significantly higher quantities for seven of the 26 individual flower compounds. A field experiment performed within a natural population, using behavioural observations and florescent dyes dusted on the flowers, could not detect any differences in pollinator visitation between colour morphs. We conclude that C. heterophylla flowers emit volatile compounds commonly associated with attraction of their most important pollinators. It would be highly interesting to explore the function of floral scent for pollinator attraction and relate floral scent to mating system variation across Collinsia for a better understanding of pollinator influence on floral evolution.

Global climatic changes may lead to the arrival of multiple range‐expanding species from different trophic levels into new habitats, either simultaneously or in quick succession, potentially causing the introduction of manifold novel interactions into native food webs. Unraveling the complex biotic interactions between native and range‐expanding species is critical to understand the impact of climate change on community ecology, but experimental evidence is lacking. In a series of laboratory experiments that simulated direct and indirect species interactions, we investigated the effects of the concurrent arrival of a range‐expanding insect herbivore in Europe, Spodoptera littoralis, and its associated parasitoid Microplitis rufiventris, on the native herbivore Mamestra brassicae, and its associated parasitoid Microplitis mediator, when co‐occurring on a native plant, Brassica rapa. Overall, direct interactions between the herbivores were beneficial for the exotic herbivore (higher pupal weight than the native herbivore), and negative for the native herbivore (higher mortality than the exotic herbivore). At the third trophic level, both parasitoids were unable to parasitize the herbivore they did not coexist with, but the presence of the exotic parasitoid still negatively affected the native herbivore (increased mortality) and the native parasitoid (decreased parasitism rate), through failed parasitism attempts and interference effects. Our results suggest different interaction scenarios depending on whether S. littoralis and its parasitoid arrive to the native tritrophic system separately or concurrently, as the negative effects associated with the presence of the parasitoid were dependent on the presence of the exotic herbivore. These findings illustrate the complexity and interconnectedness of multitrophic changes resulting from concurrent species arrival to new environments, and the need for integrating the ecological effects of such arrivals into the general theoretical framework of global invasion patterns driven by climatic change.

Field Level Auto-inoculation of Sorghum chafer, Pachnoda interrupta (Olivier) (Coleoptera: Scarabaedae) with Metarhizium anisopliae based Microbial Bio-control Agents using Locally Affordable Traps