Evaluating the Impact of Two Generalist Predators on the Leafhopper Erasmoneura vulnerata Population Density

Outbreaks of the Nearctic leafhopper Erasmoneura vulnerata represent a threat to vinegrowers in Southern Europe, in particular in North-eastern Italy. The pest outbreaks are frequent in organic vineyards because insecticides labeled for organic viticulture show limited effectiveness towards leafhoppers. On the other hand, the naturally occurring predators and parasitoids of E. vulnerata in vineyards are often not able to keep leafhopper densities at acceptable levels for vine-growers. In this study, we evaluated the potential of two generalist, commercially available predators, Chrysoperla carnea and Orius majusculus, in suppressing E. vulnerata. Laboratory and semi-field experiments were carried out to evaluate both species’ predation capacity on E. vulnerata nymphs. The experiments were conducted on grapevine leaves inside Petri dishes (laboratory) and on potted and caged grapevines (semi-field); in both experiments, the leaves or potted plants were infested with E. vulnerata nymphs prior to predator releases. Both predator species exhibited a remarkable voracity and significantly reduced leafhopper densities in laboratory and semi-field experiments. Therefore, field studies were carried out over two growing seasons in two vineyards. We released 4 O. majusculus adults and 30 C. carnea larvae per m2 of canopy. Predator releases in vineyards reduced leafhopper densities by about 30% compared to the control plots. Results obtained in this study showed that the two predators have a potential to suppress the pest density, but more research is required to define appropriate predator–prey release ratios and release timing. Studies on intraguild interactions and competition with naturally occurring predators are also suggested.

Survival and predation rate of wild-caught and commercially produced Orius majusculus (Reuter) (Hemiptera: Anthocoridae)

The quality of biological control agents used in augmentative releases may be affected by rearing conditions due to inbreeding or laboratory adaptation, or to phenotypic effects of the rearing environment. We hypothesized that individuals from a wild population would be in better body condition and kill more prey than individuals from a commercially produced population. We caught wild Orius majusculus (Reuter) in a maize field and compared their initial body mass, survival, and prey reduction capacity to commercially produced O. majusculus. Predation capacity and survival were compared in short-term Petri dish tests with Frankliniella tenuicornis (Uzel) thrips, Ephestia kuehniella (Zeller) moth eggs, or Rhopalosiphum padi (L.) aphids as prey, and in longer-term outdoor mesocosms containing live seedling wheat grass with thrips or aphids as prey. Wild-caught O. majusculus were typically heavier and overall had higher survival during tests than commercially produced O. majusculus. Females were heavier than males and typically killed more prey. However, we found no difference between wild-caught and commercially produced individuals on prey reduction, neither in Petri dishes nor in mesocosms. Our study suggests that commercially produced O. majusculus have lower body condition than wild O. majusculus due to their lower body mass and survival, but that this does not have any negative effect on the number of pest prey killed over the timelines and conditions of our tests. Commercially produced O. majusculus thus did not have a lower impact on pest prey numbers than wild-caught individuals and therefore had similar biological control value under our study conditions.

Studies Aimed at Evaluating the Impact of Generalist Predators on the Leafhopper Erasmoneura vulnerata Populations

Outbreaks of the Nearctic leafhopper Erasmoneura vulnerata represent a recent issue for winegrowers in Southern Europe, in particular in North-eastern Italy. Problems are frequent in organic vineyards because insecticides labeled for organic viticulture show limited effectiveness towards leafhoppers. On the other hand, the response by naturally occurring predators and parasitoids to E. vulnerata populations in vineyards is often unable to keep leafhopper densities under levels that are acceptable for winegrowers. Here we evaluated the potential of two generalist predators, i.e., Chrysoperla carnea and Orius majusculus, in controlling E. vulnerata populations. Laboratory and semi-field experiments were carried out to evaluate both species' predation capacity on E. vulnerata nymphs. Then, predators were released in vineyards colonized by large E. vulnerata populations. Both predator species exhibited a remarkable voracity in the laboratory and significantly reduced leafhopper densities in semi-field experiments. Predator releases in vineyards reduced leafhopper densities by about 30%. Results obtained in laboratory, semi-field, and field experiments are discussed to implement these biocontrol agents' use in pest control tactics.

Laboratory assessment of the suitability of predatory bugs Orius laevigatus and Orius majusculus as natural enemies of seed potato pests in greenhouses

Laboratory experiments were performed to test Orius majusculus and Orius laevigatus suitability for potato protection. The adult bugs released on potato plants infested with Myzus persicae can normally survive, mature, and reproduce. In the absence of prey, the bugs can survive for about a week. And though addition of flower pollen increased survival, insect fecundity remained low. Only feeding by Sitotroga cerealella eggs added to potato plants provided for sustainable fecundity of Orius females laying up to 200 eggs during the lifetime. Thus, O. majusculus can be applied for biological control of aphids on seed potatoes in greenhouses and the grain moth eggs can be used as an additional food for the bugs.

Stable Isotope Enrichment (Δ15N) in the Predatory Flower Bug (Orius majusculus) Predicts Fitness-Related Differences between Diets

Mass rearing of insects, used both as biological control agents and for food and feed, is receiving increasing attention. Efforts are being made to improve diets that are currently in use, and to identify alternative diets, as is the case with the predatory flower bug (Orius majusculus) and other heteropteran predators, due to the high costs of their current diet, the eggs of the Mediterranean flour moth (E. kuehniella). The assessment of alternative diets may include measurements of the predator’s fitness-related traits (development time, weight, etc.), and biochemical analyses such as lipid and protein content in the diet and the insects. However, assessing diet quality via the predator’s fitness-related traits is laborious, and biochemical composition is often difficult to relate to the measured traits. Isotope analysis, previously used for diet reconstruction studies, can also serve as a tool for the assessment of diet quality. Here, the variation in discrimination factors or isotope enrichment (Δ15N and Δ13C) indicates the difference in isotopic ratio between the insect and its diet. In this study, we investigated the link between Δ15N and diet quality in the predatory bug Orius majusculus. Three groups of bugs were fed different diets: Ephestia kuehniella eggs, protein-rich Drosophila melanogaster and lipid-rich D. melanogaster. The isotopic enrichment and fitness-related measurements were assessed for each group. Results show a relation between Δ15N and fitness-related measurements, which conform to the idea that lower Δ15N indicates a higher diet quality.