Agriculturally Intensified Landscapes Are Associated With Reduced Body Condition of Lady Beetles

Context: Agricultural intensification is contributing to a global species decline. Underlying mechanisms include toxic effects of pesticides on non-target organisms and reductions in habitat and food availability. However, the effects of agricultural intensification on body condition, particularly of ecosystem service providing arthropods, are poorly understood.Objectives: Here, we investigated whether variations in the body condition of common lady beetle species (Coleoptera: Coccinellidae) can be explained by the composition and configuration of the surrounding landscape. Assuming strong seasonal variation in food availability in intensively farmed regions, we included the entire period of lady beetle activity in our study.Methods: Lady beetles were collected from April to September 2011 in 30 landscapes in southern Wisconsin, USA. We examined how body size, body density, and lipid content of the beetles responded to the percentage of intensive cropland, habitat diversity, and edge density in the surrounding landscape.Results: The strongest predictor of body condition was the percentage of intensive cropland. For every 10% increase in cropland, body density decreased by about 3.9% and fat content by 6.4%. Landscape diversity and edge density correlated with body condition of individual species.Conclusions: In agriculturally intensified landscapes, lady beetles with reduced body condition may produce fewer offspring, have lower survival rates, and exert less effective pest control. Thus, our results suggest a mechanistic link between landscape patterns and observed declines in lady beetle populations. Our results also show that the expansion of monocultures affects even common cropland-associated species such as Harmonia axyridis, suggesting a long-term decline in biocontrol services in simplified agricultural landscapes.

Interactions of ants with native and invasive lady beetles and the role of chemical cues in intraguild interference

The predator-predator naïveté hypothesis suggests that non-native predators benefit from being unknown to native predators, resulting in reduced intraguild interference with native predators. This novelty advantage should depend on the ability of native predators to recognize cues of non-native predators. Here, we compared ant aggression and lady beetle reaction in four native and the invasive lady beetle species Harmonia axyridis. In addition, we tested whether lady beetle cuticular hydrocarbons (CHCs) are involved in species recognition, which might explain naïveté if the invasive species has a specific CHC profile. To this end, we conducted behavioral assays confronting two native ant species with both living lady beetles and lady beetle elytra bearing or lacking CHCs of different lady beetle species. Finally, we characterized CHC profiles of the lady beetles using GC–MS. In general, the aggression of Lasius niger was more frequent than that of Myrmica rubra and L. niger aggression was more frequent towards most native lady beetle species compared to H. axyridis. The removal of CHCs from lady beetle elytra reduced aggression of both ant species. If CHCs of respective lady beetle species were added on cue-free elytra, natural strength of L. niger aggression could be restored. CHC analyses revealed a distinct cue composition for each lady beetle species. Our experiments demonstrate that the presence of chemical cues on the surface of lady beetles contribute to the strength of ant aggression against lady beetles. Reduced aggression of L. niger towards H. axyridis and reduced avoidance behavior in H. axyridis compared to the equally voracious C. septempunctata might improve the invasive lady beetle’s access to ant-tended aphids.

Diversity Loss and Restructuring of the Microbiota in a Globally Invasive Lady Beetle

The invasion success of Harmonia axyridis in North America and Europe has aroused a growing interest among students of invasion biology. This study was focused on the microbial community of H. axyridis with the aim of gaining insights into their potential roles in the invasion. We hypothesized that microbial communities of H. axyridis in the non-native range may decrease in diversity but restructured in composition as compared to those in the native regions. We collected lady beetle samples from eleven geographical areas across the native range mainland China and from seven areas in the non-native range USA. We applied next-generation amplicon sequencing to the samples to estimate microbial communities and examined differences in their composition and diversity between the host’s native and non-native ranges. We found that H. axyridis in the non-native range had lower microbial community richness and evenness than it had in the native range, but its microbiota composition of the amplicon sequence variants and genera differed markedly between the non-native and native ranges. The findings support our hypotheses concerning microbial community in H. axyridis across the native and non-native range. This study provides new information for our understanding of potential roles of the microbiota in the invasion success of H. axyridis.

Evaluation of compounds for repellency of the multicoloured Asian lady beetle (Coleoptera: Coccinellidae) in vineyards

The multicoloured Asian lady beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), has become a pest in North American vineyards during harvest due to its adverse effects on wine quality. This study evaluated alternative products that may be suitable for use in vineyards as repellents to the beetle. Products were screened as repellent for multicoloured Asian lady beetle in short-term laboratory trials. Thirteen products significantly reduced the number of beetles on grapes, Vitis vinifera (Vitaceae). Products that showed a 50% or greater repellency were evaluated for residual repellency 24, 48, and 72 hours after application. In these trials, pine oil was highly repellent at each testing period, whereas the repellency of most other products decreased over time. Eight repellent compounds were evaluated in field trials in commercial vineyards that had high multicoloured Asian lady beetle populations. The number of beetles on vines was counted 2–6 and 24–28 hours after application. In the field, the most effective repellents overall were Biobenton and Buran, which reduced the number of multicoloured Asian lady beetles by 39 and 34%, respectively. The discovery of new repellents of multicoloured Asian lady beetle provides an opportunity to improve management of the pest in vineyards and to reduce risk of wine taint without using broad-spectrum insecticides.