Plant versus pollinator protection: balancing pest management against floral contamination for insecticide use in Midwestern US cucurbits.

Controlling crop pests while conserving pollinators is challenging, particularly when prophylactically applying broad-spectrum, systemic insecticides such as neonicotinoids. Systemic insecticides are often used in conventional agriculture in commercial settings, but the conditions that optimally balance pest management and pollination are poorly understood. We investigated how insecticide application strategies control pests and expose pollinators to insecticides with an observational study of cucurbit crops in the Midwestern United States. To define the window of protection and potential pollinator exposure resulting from alternative insecticide application strategies, we surveyed 62 farms cultivating cucumber, watermelon, or pumpkin across 2 yr. We evaluated insecticide regimes, abundance of striped and spotted cucumber beetles (Acalymma vittatum [Fabricius] and Diabrotica undecimpunctata Mannerheim), and insecticide residues in leaves, pollen, and nectar. We found that growers used neonicotinoids (thiamethoxam and imidacloprid) at planting in all cucumber and pumpkin and approximately half of watermelon farms. In cucumber, foliar thiamethoxam levels were orders of magnitude higher than the other crops, excluding nearly all beetles from fields. In watermelon and pumpkin, neonicotinoids applied at planting resulted in 4-8 wk of protection before beetle populations increased. Floral insecticide concentrations correlated strongly with foliar concentrations across all crops, resulting in high potential exposure to pollinators in cucumber and low-moderate exposure in pumpkin and watermelon. Thus, the highest-input insecticide regimes maintained cucumber beetles far below economic thresholds while also exposing pollinators to the highest pollen and nectar insecticide concentrations. In cucurbits, reducing pesticide inputs will likely better balance crop protection and pollination, reduce costs, and improve yields.

A newly invasive species may promote dissimilarity of pest populations between organic and conventional farming systems.

Insect taxa vary in their phenology across space creating dissimilar patterns of species abundance over time. The role of human disturbances and invasive species in these patterns of temporal dissimilarity (phenological differences) across space, however, remain largely unexplored. To dissect these patterns, we evaluated four common pests and one newly invasive species (Contarinia nasturtii; Swede midge) at 220 time points across 2 years on organic and conventional farms. We first summarized across time and evaluated differences in pest abundance between farm management (organic and conventional). We then used generalized additive models to describe temporal patterns of abundance, disentangling phenological differences across management systems. Last, we conducted a temporal beta diversity analysis to identify which species and management practices contribute most to dissimilarity. We found that aggregating pest abundance across time and species masked differences in pest phenology across management systems and concealed variation in pest abundance that was strongly driven by an invasive species, respectively. Overall, our results suggest that organic and conventional farms may be only superficially similar in pest abundance. Rather, by accounting for time, we demonstrate a more nuanced understanding of pest communities moving beyond abundance that may be particularly important for management of newly invasive species.

Documenting pollinators, floral hosts, and plant-pollinator interactions in U.S. Pacific Northwest agroecosystems.

The abundance and diversity of pollinator populations are in global decline. Managed pollinator species, like honey bees, and wild species are key ecosystem service providers in both natural and managed agroecosystems. However, relatively few studies have exhaustively characterized pollinator populations in diverse agroecosystems over multiple years, while also thoroughly documenting plant-pollinator interactions. Yet, such studies are needed to fulfill the national pollinator protection plans that have been released by the United States and other nations. Our research is among the first studies to respond to these directives by systematically documenting bee and plant biodiversity, bee-plant interactions, and bee-mediated pollen movement in farming systems of the Pacific Northwest, USA. Our data provides insight into the processes mediating pollinator and plant community assembly, persistence, and resilience across landscapes with variable crop and landscape diversity and agroecosystem management practices. These data will also contribute to the development of a United States pollinator database, supporting the United States' plan to promote pollinators. With few publicly available data sets that systematically take account of agroecosystem practices, plant populations, and pollinators, our research will provide future users the means to conduct synesthetic studies of pollinators and ecosystem function in a period of rapid and global pollinator declines. There are no copyright or proprietary restrictions for research or teaching purposes. Usage of the data set must be cited.

Plant evolution can mediate negative effects from honey bees on wild pollinators.

Pollinators are introduced to agroecosystems to provide pollination services. Introductions of managed pollinators often promote ecosystem services, but it remains largely unknown whether they also affect evolutionary mutualisms between wild pollinators and plants.Here, we developed a model to assess effects of managed honey bees on mutualisms between plants and wild pollinators. Our model tracked how interactions among wild pollinators and honey bees affected pollinator and plant populations.We show that when managed honey bees have a competitive advantage over wild pollinators, or a greater carrying capacity, the honey bees displace the wild pollinator. This leads to reduced plant density because plants benefit less by visits from honey bees than wild pollinators that coevolved with the plants.As wild pollinators are displaced, plants evolve by increasing investment in traits that are attractive for honey bees but not wild pollinators. This evolutionary switch promotes wild pollinator displacement. However, higher mutualism investment costs by the plant to the honey bee can promote pollinator coexistence.Our results show plant evolution can promote displacement of wild pollinators by managed honey bees, while limited plant evolution may lead to pollinator coexistence. More broadly, effects of honey bees on wild pollinators in agroecosystems, and effects on ecosystem services, may depend on the capacity of plant populations to evolve.

A novel plant pathogen management tool for vector management.

BACKGROUND: Decision support systems often focus on insect control due to direct damage. However, when insects vector plant pathogens, these decision support systems must be tailored to disease management. However, a decision system that links diagnosticians to vector management is lacking and complicated by patterns of insect abundance over space and time. Here, we describe an approach that integrated monitoring of an insect pest (aster leafhopper; Macrosteles quadrilineatus, Forbes) that vectors aster yellows phytoplasma (Candidatus Phytoplasma spp.), with rapid disease diagnostics and web-based text messaging in two crops, carrots and celery. RESULTS: From 2014-2019, a total of 8,343 aster leafhoppers were collected, 99 of these were infected with phytoplasma. Text messaging reduced the number of infected leafhoppers. When we compared infected leafhopper density across crops, their temporal patterns were most similar at a 2-week delay. Comparisons within crop indicated that in celery uninfected and infected leafhopper density was most similar at a 2-week delay, but there was no similar pattern in carrots. Leafhopper density and infectivity were not similar beyond individual farms. CONCLUSION: Our results suggest that farmers should account for these temporal and spatial patterns when managing leafhoppers infected with aster yellows phytoplasma to improve pest management. By combining extensive monitoring, with rapid disease diagnostics, and text messaging, we demonstrate the value of our decision support tool. © 2020 Society of Chemical Industry.

Landscape structure and climate drive population dynamics of an insect vector within intensely managed agroecosystems.

Characterizing factors affecting insect pest populations across variable landscapes is a major challenge for agriculture. In natural ecosystems, insect populations are strongly mediated by landscape and climatic factors. However, it has proven difficult to evaluate if similar factors predict pest dynamics in agroecosystems because control tactics exert strong confounding effects. We addressed this by assessing whether species distribution models could effectively characterize dynamics of an insect pest in intensely managed agroecosystems. Our study used a regional multi-year data set to assess landscape and climatic drivers of potato psyllid (Bactericera cockerelli) populations, which are often subjected to calendar-based insecticide treatments because they transmit pathogens to crops. Despite this, we show that psyllid populations were strongly affected by landscape and climatic factors. Psyllids were more abundant in landscapes with high connectivity, low crop diversity, and large natural areas. Psyllid population dynamics were also mediated by climatic factors, particularly precipitation and humidity. Our results show that many of the same factors that drive insect population dynamics in natural ecosystems can have similar effects in an intensive agroecosystem. More broadly, our study shows that models incorporating landscape and climatic factors can describe pest populations in agroecosystems and may thus promote more sustainable pest management.

A novel application of the Price equation reveals that landscape diversity promotes the response of bees to regionally rare plant species.

Bees are ecosystem service providers that are globally threatened by losses of plant diversity. However, effects of multi-species floral displays on bees in agro-ecosystems with variable landscape context remain poorly understood, hindering pollinator conservation tactics. We addressed this knowledge gap through a novel application of the modified Price equation to evaluate responses of bees to diverse floral communities on 36 farms in Washington, USA, over 3 years. We found that floral richness, not floral identity, was the best predictor of floral visits by bees. However, the benefits of regionally rare floral species (i.e. plants found at relatively few sites) were only fully realised when farms were embedded in diverse landscapes. Our analysis used the modified Price equation to demonstrate that plant diversity, rather than specific plant species, promotes pollinator visitation, and that diverse landscapes promote the response of pollinators to regionally rare plant species.