ABSTRACT
Bagrada bug, Bagrada hilaris (Burmeister) (Hemiptera: Pentatomidae), is an invasive pest of cruciferous crops. The parasitoid Gryon aetherium Talamas (Hymenoptera: Scelionidae) is a promising biological control agent for B. hilaris because it can forage in the soil where B. hilaris deposits most of its eggs. In this study, we assessed parasitism by G. aetherium on B. hilaris eggs in situ in northcentral California, including the Salinas Valley where most cruciferous crops in the United States are grown. Parasitism was documented by leaving soil-filled trays under infested plants for 7-14 days, then removing eggs and holding them for emergence of parasitoids. Gryon aetherium accounted for over 99% of emerged parasitoids, and occurred at 11 of the 12 sampled sites. Of the 17,729 and 31,759 B. hilaris eggs collected in 2021 and 2022, 1,518 (8.84%) and 2,654 (8.36%) were parasitized by G. aetherium, respectively. Parasitism rates were generally higher inland and ranged from 3.64% to 44.93% in 2021 and from 1.01% to 23.04% in 2022, and never exceeded 15% on any sample dates at several coastal sites in the Salinas Valley. Discovery efficiency (a measure of the ability of parasitoids to locate egg patches) reached 80% or higher at all but 1 site, but exploitation efficiency (a measure of the ability of parasitoids to exploit the egg patch after it has been discovered) was generally <20%, suggesting that G. aetherium can locate egg patches efficiently but is less efficient at finding eggs within patches.
ABSTRACT
We found that vittatalactone, specifically (3R,4R)-3-methyl-4-[(1S,3S,5S)-1,3,5,7-tetramethyloctyl]oxetan-2-one, is the male-produced aggregation pheromone of the western striped cucumber beetle, Acalymma trivittatum (Mannerheim), as was previously shown for the striped cucumber beetle, Acalymma vittatum (F.) (Coleoptera: Chrysomelidae). A synthetic mixture containing 9% of the authentic natural pheromone, is attractive to both sexes of both species in the field, as demonstrated by trapping using baited and unbaited sticky panels in California and earlier in Maryland. Females of both species do not produce detectable vittatalactone. This finding expands the usefulness of the synthetic vittatalactone mixture for pest management throughout the range of both A. vittatum and A. trivittatum. Development of vittatalactone time-release formulations combined with cucurbitacin feeding stimulants offer the potential for selective and environmentally-friendly cucurbit pest management tactics.
Subject(s)
Coleoptera , Cucumis sativus , Male , Female , Animals , Pheromones/pharmacology , Lactones/pharmacologyABSTRACT
Bagrada hilaris (Burmeister) (Hemiptera: Pentatomidae) is an invasive stink bug species that feeds on cruciferous plants and can cause substantial damage to crops. Little is known about the dispersal behavior of B. hilaris, but movement is important because of the way this pest moves from senescing weed hosts into crop fields. Perhaps, B. hilaris residing on declining weed hosts become starved, which alters their normal locomotor activity and initiates dispersal. We examined the influence of starvation on the locomotor behavior of multiple life stages of B. hilaris under laboratory and outdoor conditions. We starved nymph (2nd/3rd and 4th/5th instars) and adult (female and male) stages for 0, 24, and 48 h. We measured distance moved in the laboratory and then distance moved and turning ratio outdoors. In the laboratory, the younger nymphs moved shortest distances when starved for 24 h, whereas late-instar nymphs (4th-5th instars) and adult B. hilaris that were starved moved farther than non-starved individuals. In the outdoor setting, environmental conditions, specifically surface temperature were important in determining how starvation affected distance moved. Starved insects were more responsive (moved farther) for a given change in temperature than non-starved insects. At lower temperatures, B. hilaris tended to move farther when non-starved and at higher temperatures, moved longer distances when starved, at least for certain stages. Increased starvation also led to more directional movement. Our results indicate that starvation influences aspects of movement for B. hilaris and that these effects can be influenced by temperature.
Subject(s)
Hemiptera , Introduced Species , Starvation , Walking , Animals , Female , Male , NymphABSTRACT
Much research has explored the effects of plant species diversity on herbivore populations, but far less has considered effects of plant genotypic diversity, or how abiotic stressors, like drought, can modify effects. Mechanisms by which plant genotypic diversity affects herbivore populations remain largely unresolved. We used greenhouse studies with a model system of wheat (Triticum aestivum L.) and bird cherry-oat aphid (Rhopalosiphum padi L.) to determine whether the genotypic diversity of a plant's neighborhood influences performance and fitness of herbivores on a focal plant and if drought changes the influence of neighborhood diversity. Taken across all varieties we tested, plant-plant interactions in diverse neighborhoods reduced aphid performance and generated associational resistance, although effects on aphids depended on variety identity. In diverse mixtures, drought stress greatly diminished the genotypic diversity-driven reduction in aphid performance. Neighborhood diversity influenced mother aphid size, and appeared to partially explain how plant-plant interactions reduced the number of offspring produced in mixtures. Plant size did not mediate effects on aphid performance, although neighborhood diversity reduced plant mass across varieties and watering treatments. Our results suggest inter-varietal interactions in genotypic mixtures can affect herbivore performance in the absence of herbivore movement and that abiotic stress may diminish any effects. Accounting for how neighborhood diversity influences resistance of an individual plant to herbivores will help aid development of mixtures of varieties for managing insect pests and clarify the role of plant genotypic diversity in ecosystems.
