Crop pests and predators exhibit inconsistent responses to surrounding landscape composition

The idea that noncrop habitat enhances pest control and represents a win–win opportunity to conserve biodiversity and bolster yields has emerged as an agroecological paradigm. However, while noncrop habitat in landscapes surrounding farms sometimes benefits pest predators, natural enemy responses remain heterogeneous across studies and effects on pests are inconclusive. The observed heterogeneity in species responses to noncrop habitat may be biological in origin or could result from variation in how habitat and biocontrol are measured. Here, we use a pest-control database encompassing 132 studies and 6,759 sites worldwide to model natural enemy and pest abundances, predation rates, and crop damage as a function of landscape composition. Our results showed that although landscape composition explained significant variation within studies, pest and enemy abundances, predation rates, crop damage, and yields each exhibited different responses across studies, sometimes increasing and sometimes decreasing in landscapes with more noncrop habitat but overall showing no consistent trend. Thus, models that used landscape-composition variables to predict pest-control dynamics demonstrated little potential to explain variation across studies, though prediction did improve when comparing studies with similar crop and landscape features. Overall, our work shows that surrounding noncrop habitat does not consistently improve pest management, meaning habitat conservation may bolster production in some systems and depress yields in others. Future efforts to develop tools that inform farmers when habitat conservation truly represents a win–win would benefit from increased understanding of how landscape effects are modulated by local farm management and the biology of pests and their enemies

Identifying Leafhopper Targets for Controlling Aster Yellows in Carrots and Celery

Aster yellows phytoplasma (Candidatus Phytoplasma asteris) is a multi-host plant pathogen and is transmitted by at least 24 leafhopper species. Pathogen management is complex and requires a thorough understanding of vector dynamics. In the American Midwest, aster yellows is of great concern for vegetable farmers who focus on controlling one vector, Macrosteles quadrilineatus—the aster leafhopper. However, vegetable-associated leafhopper communities can be diverse. To investigate whether additional species are important aster yellows vectors, we surveyed leafhopper communities at commercial celery and carrot farms in Michigan from 2018 to 2019 and conducted real-time PCR to determine infection status. Leafhoppers were collected within crop fields and field edges and identified with DNA barcoding. Overall, we collected 5049 leafhoppers, with the most abundant species being M. quadrilineatus (57%) and Empoasca fabae—the potato leafhopper (23%). Our results revealed the most abundant aster yellows vector in Michigan in both crops is M. quadrilineatus, but we also found that E. fabae may be a potential vector for this pathogen. While several taxa reside in and near these crops, we did not find strong evidence that they contribute to phytoplasma infection. These findings indicate that M. quadrilineatus should be the primary target for controlling this pathogen

Elucidating the Common Generalist Predators of Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae) in an Organic Apple Orchard Using Molecular Gut-Content Analysis

Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), plum curculio, is a serious direct pest of North American tree fruit including, apples, cherries, peaches and plums. Historically, organophosphate insecticides were used for control, but this tool is no longer registered for use in tree fruit. In addition, few organically approved insecticides are available for organic pest control and none have proven efficacy as this time. Therefore, promoting biological control in these systems is the next step, however, little is known about the biological control pathways in this system and how these are influenced by current mechanical and cultural practices required in organic systems. We used molecular gut-content analysis for testing field caught predators for feeding on plum curculio. During the study we monitored populations of plum curculio and the predator community in a production organic apple orchard. Predator populations varied over the season and contained a diverse assemblage of spiders and beetles. A total of 8% of all predators (eight Araneae, two Hemiptera, and six Coleoptera species) assayed for plum curculio predation were observed positive for the presence of plum curculio DNA in their guts, indicating that these species fed on plum curculio prior to collection Results indicate a number of biological control agents exist for this pest and this requires further study in relation to cultural practices

Molecular Diagnostic for Boll Weevil (Coleoptera: Curculionidae) Based on Amplification of Three Species-Specific Microsatellites

The boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), is a serious pest of cultivated cotton, Gossypium hirsutum L., in the Americas, and reinfestation of zones from which they have been eradicated is of perpetual concern. Extensive arrays of pheromone traps monitor for reintroductions, but occasionally the traps collect nontarget weevils that can be misidentified by scouts. For example, the congeneric pepper weevil, Anthonomus eugenii Cano, and other superficially similar weevils are attracted to components of the boll weevil lure or trap color. Although morphologically distinguishable by trained personnel, the potential for misidentification is compounded when captured weevils are dismembered or partially consumed by ants or ground beetles that sometimes feed on them in the traps. Because misidentification can have expensive consequences, a molecular diagnostic tool would be of great value to eradication managers. We demonstrate that a cocktail of three primer pairs in a single polymerase chain reaction (PCR) amplify species-specific microsatellites that unambiguously distinguish the boll weevil from three other weevil species tested, including pepper weevil; cranberry weevil, Anthonomus eugenii musculus Say; and pecan weevil, Curculio caryae Horn. However, it does not distinguish the boll weevil from the subspecific “thurberia” weevil. A universal internal transcribed spacer primer pair included in the cocktail cross-amplifies DNA from all species, serving as a positive control. Furthermore, the diagnostic primers amplified the target microsatellites from various boll weevil adult body parts, indicating that the PCR technology using the primer cocktail is sensitive enough to positively identify a boll weevil even when the body is partly degraded

5. Analysis file for individual plant species composition on neonicotinoid concentration

Analysis file containing neonicotinoid residue data and plant species composition of pollen load data

1. Landscape composition data at 1500 m radius

Landscape composition data for the 24 selected sites at a 1500 m radius

Data from: Honey bee dietary neonicotinoid exposure is associated with pollen collection from agricultural weeds

Neonicotinoid insecticides have been linked to bee declines. However, tracking the primary exposure route for bees in the field has proven to be a major logistical challenge, impeding efforts to restore pollinator health in agricultural landscapes. We quantified neonicotinoid concentrations and botanical species composition in 357 pollen samples collected from 114 commercial honey bee colonies placed along a gradient of agricultural intensity between June and September. Neonicotinoid concentrations increased through the season, peaking at the end of August. As a result, concentrations in pollen were negatively associated with collection from woody and crop plants that flower early-mid season, and positively associated with collection from herbaceous plants that flower mid-late season. Higher clothianidin and thiamethoxam residues were correlated with samples containing a greater proportion of pollen collected from agricultural weeds. The percentage of agricultural land within 1,500 m was positively correlated with thiamethoxam concentration; however, this spatial relationship was far weaker than the relationship with the proportion of pollen collected from herbaceous plants. These results indicate that both plant species identity and agricultural dominance are important in determining honey bee neonicotinoid exposure through the pollen diet, but that uncultivated plants associated with agriculture are the source of the greatest acute exposure

2. Neonicotinoid residues detected in collected pollen samples

Neonicotinoid residues (thiamethoxam, clothianidin, and imidacloprid) detected in honey bee-collected pollen samples at both the sample and trapping event scale

3. Pollen composition data

Identity and proportion data for the honey bee pollen load