Diet specialization mediates drivers of Cucurbita herbivory in a semi-arid agroecosystem.

Herbivory is a major fitness pressure for plants and a key driver of crop losses in agroecosystems. Dense monocultures are expected to favor specialist herbivorous insects, particularly those who primarily consume crop species; yet, levels and types of herbivory are not uniform within regional cropping systems. It is essential to determine which local and regional ecological factors drive variation in herbivory in order to support functional agroecosystems that rely less on chemical inputs. Crops in the genus Cucurbita host a suite of both generalist and specialist herbivores that inflict significant damage, yet little is known about the relative contribution of these herbivores to variation in herbivory and how local- and landscape-scale Cucurbita resource concentrations, management practices, and natural enemies mediate this relationship. In this study, we tested whether three foundational ecological hypotheses influenced Cucurbita herbivory across 20 pumpkin fields in the semi-arid Southern High Plains Region of Texas. We used generalized linear mixed models and confirmatory path analysis to assess whether the Density-dependent Herbivory Hypothesis, Resource Concentration Hypothesis, or the Natural Enemies Hypothesis, could explain variation in Cucurbita herbivory and insect dynamics in the context of conventional agronomic practices. We found that herbivory increased over time, indicating that herbivores were causing sustained damage throughout the growing season. We also found that fields with higher local Cucurbita resources had lower herbivory, suggesting a resource dilution effect. Natural enemy communities were more abundant and taxonomically rich in sites with greater generalist herbivore abundance, though predator abundance declined over time, indicating that late-season crop fields are most at risk given high herbivory and low natural enemy-based control. Our findings also suggest that while local resource availability may drive the abundance and richness of arthropod communities, additional agronomic and phenological information is needed to anticipate herbivory risk in an agriculturally dominated landscape.

Nectar Source and Pollinator Cross Contamination and Persistence of Pyriproxyfen Associated with the Use of Autodissemination Techniques for Mosquito Control.

Controlling container inhabiting mosquitoes such as Aedes aegypti and Ae. albopictus is often difficult because of the requirement to treat small and inaccessible cryptic sources of water where larvae are located. Autodissemination approaches based on the dissemination of insect growth regulators (IGRs) have been demonstrated as an effective means to treat these cryptic larval habitats and provide population control. Autodissemination approaches are attractive because they are based on the mosquitoes disseminating small amounts of IGRs compared to more traditional insecticide applications. While dissemination of small amounts of IGRs seems like an advantage, these approaches could lead to unintended transfer and effects on nontarget insect pollinators by delivering highly potent IGRs to nectar sources. Here we looked for the indirect and direct transfer of pyriproxyfen (PPF) to natural and artificial nectar sources and painted lady butterflies, Vanessa cardui, in semifield cages using the release of treated Ae. albopictus males or an autodissemination station. We also performed persistence tests of PPF in oviposition containers and natural and artificial nectar sources when exposed to laboratory and natural conditions. The data suggest that there is direct and indirect transfer to nectar sources and V. cardui associated with the use of autodissemination approaches. We discuss the results in the context of using autodissemination approaches for mosquito control and the potential risks these approaches may pose to nontarget insect pollinators.

Indirect transfer of pyriproxyfen to European honeybees via an autodissemination approach.

The frequency of arboviral disease epidemics is increasing and vector control remains the primary mechanism to limit arboviral transmission. Container inhabiting mosquitoes such as Aedes albopictus and Aedes aegypti are the primary vectors of dengue, chikungunya, and Zika viruses. Current vector control methods for these species are often ineffective, suggesting the need for novel control approaches. A proposed novel approach is autodissemination of insect growth regulators (IGRs). The advantage of autodissemination approaches is small amounts of active ingredients compared to traditional insecticide applications are used to impact mosquito populations. While the direct targeting of cryptic locations via autodissemination seems like a significant advantage over large scale applications of insecticides, this approach could actually affect nontarget organisms by delivering these highly potent long lasting growth inhibitors such as pyriproxyfen (PPF) to the exact locations that other beneficial insects visit, such as a nectar source. Here we tested the hypothesis that PPF treated male Ae. albopictus will contaminate nectar sources, which results in the indirect transfer of PPF to European honey bees (Apis mellifera). We performed bioassays, fluorescent imaging, and mass spectrometry on insect and artificial nectar source materials to examine for intra- and interspecific transfer of PPF. Data suggests there is direct transfer of PPF from Ae. albopictus PPF treated males and indirect transfer of PPF to A. mellifera from artificial nectar sources. In addition, we show a reduction in fecundity in Ae. albopictus and Drosophila melanogaster when exposed to sublethal doses of PPF. The observed transfer of PPF to A. mellifera suggests the need for further investigation of autodissemination approaches in a more field like setting to examine for risks to insect pollinators.

Use of nest bundles to monitor agrochemical exposure and effects among cavity nesting pollinators.

Cavity nesting bees are proficient and important pollinators that can augment or replace honey bee pollination services for some crops. Relatively little is known about specific pesticide concentrations present in cavity nesting insect reed matrices and associated potential risks to cavity nesting bees. Nesting substrates (Phragmites australis reeds in bundles) were deployed in an agriculturally intensive landscape to evaluate colonization and agrochemical exposure among cavity nesting pollinators over two consecutive field seasons. Composition of insect species colonizing reeds within nest bundles varied considerably; those placed near beef cattle feed yards were dominated by wasps (93% of the total number of individuals occupying reed nest bundles), whereas nest bundles deployed in cropland-dominated landscapes were colonized primarily by leaf cutter bees (71%). All nesting/brood matrices in reeds (mud, leaves, brood, pollen) contained agrochemicals. Mud used in brood chamber construction at feed yard sites contained 21 of 23 agrochemicals included in analysis and >70% of leaf substrate stored in reeds contained at least one agrochemical. Moxidectin was most frequently detected across all reed matrices from feed yard sites, and moxidectin concentrations in nonviable larvae were more than four times higher than those quantified in viable larvae. Agrochemical concentrations in leaf material and pollen were also quantified at levels that may have induced toxic effects among developing larvae. To our knowledge, this is the first study to characterize agrochemical concentrations in multiple reed matrices provisioned by cavity-nesting insects. Use of nest bundles revealed that cavity nesting pollinators in agriculturally intensive regions are exposed to agrochemicals during all life stages, at relatively high frequencies, and at potentially lethal concentrations. These results demonstrate the utility of nest bundles for characterizing risks to cavity nesting insects inhabiting agriculturally intensive regions.

Exposure of Foraging Bees (Hymenoptera) to Neonicotinoids in the U.S. Southern High Plains.

Exposure to pesticides is a major threat to insect pollinators, potentially leading to negative effects that could compromise pollination services and biodiversity. The objectives of this study were to quantify neonicotinoid concentrations among different bee genera and to examine differences attributable to body size and surrounding land use. During the period of cotton planting (May-June), 282 wild bees were collected from habitat patches associated with cropland, grassland, and urban land cover and analyzed for three neonicotinoids (thiamethoxam, clothianidin, and imidacloprid). Twenty bees among eight genera contained one or more of the neonicotinoid compounds and detections occurred in all landscape types, yet with the most detections occurring in cropland-associated habitats. Apis Linnaeus (Hymenoptera: Apidae), Melissodes Latreille (Apidae), Perdita Smith (Andrenidae), and Lasioglossum Curtis (Halictidae) had multiple individuals with neonicotinoid detections. Two of the largest bees (Apis and Melissodes) had the greatest number of detections within genera, yet the relatively small-bodied genus Perdita had the three highest neonicotinoid concentrations reported. The number of detections within a genus and average generic body mass showed a marginally significant trend towards larger bees having a greater frequency of neonicotinoid detections. Overall, the relatively low percentage of detections across taxa suggests practices aimed at conserving grassland remnants in intensified agricultural regions could assist in mitigating exposure of wild bees to agrochemicals, while differences in bee traits and resource use could in part drive exposure. Further work is needed to address variable agrochemical exposures among pollinators, to support strategies for conservation and habitat restoration in affected landscapes.

Sestonic Chlorophyll- Shows Hierarchical Structure and Thresholds with Nutrients across the Red River Basin, USA.

The Red River is a transboundary, multijurisdictional basin where water-quality standards are often different across state lines. The state agencies with USEPA Region VI focused resources to organize water-quality data from within this basin and have it statistically analyzed to evaluate the relationships between nutrients and sestonic chlorophyll- (chl-a). There were 152 sites within the Red River basin that had nutrient and sestonic chl-a measurements; these sites were narrowed down to 132 when a minimum number of observations was required. Sestonic chl-a levels increased with increasing nutrient concentrations; these regressions were used to predict nutrient concentrations at 10 µg chl-a L. Total nitrogen (TN) and phosphorus (TP) concentrations (at 10 µg chl-a L) varied across the Red River basin and its ecoregions from 0.10 to 0.22 mg TP L and 0.75 to 2.11 mg TN L. Nutrient thresholds were also observed with sestonic chl-a at 0.14 mg TP L and 0.74 mg TN L using categorical and regression tree analysis (CART). The CART analysis also revealed that hierarchical structure was important when attempting to predict sestonic chl-a from TN, TP, and conductivity. The ranges of TN and TP concentrations that resulted in chl-a concentrations that exceeded 10 µg chl-a L were similar in magnitude to the threshold in TN and TP that resulted in increased sestonic chl-a. This corroborating evidence provides useful guidance to the states with jurisdiction within the Red River basin for establishing nutrient criteria, which may be similar when the Red River and its tributaries cross political boundaries.

Biological assessment to support ecological recovery of a degraded headwater system.

An assessment of the benthic macroinvertebrate community was conducted to characterize the ecological recovery of a channelized main stem and two small tributaries at the Watershed Research and Education Center (WREC, Arkansas, USA). Three other headwater streams in the same basin were also sampled as controls and for biological reference information. A principal components analysis produced stream groupings along an overall gradient of physical habitat integrity, with degraded reaches showing lower RBP habitat scores, reduced flow velocities, smaller substrate sizes, greater conductivity, and higher percentages of sand and silt substrate. The benthic macroinvertebrate assemblage at WREC was dominated by fast-reproducing dipteran larvae (midge and mosquito larvae) and physid snails, which comprised 71.3% of the total macroinvertebrate abundance over three sampling periods. Several macroinvertebrate assemblage metrics should provide effective targets for monitoring overall improvements in the invertebrate assemblage including recovery towards a more complex food web (e.g., total number of taxa, number of EPT taxa, percent 2 dominant taxa). However, current habitat conditions and the extent of existing degradation, system isolation and surrounding urban or agricultural land-uses might affect the level of positive change to the system. We therefore suggest a preliminary restoration strategy involving the addition of pool habitats in the system. At one pool we collected a total of 29 taxa (dominated by water beetle predators), which was 59% of total number of taxa collected at WREC. Maintaining water-retentive pools to collect flows and maintain water permanence focuses on enhancing known biology and habitat, thus reducing the effects of abiotic filters on macroinvertebrate assemblage recovery. Furthermore, biological assessment prior to restoration supports a strategy primarily focused on improving the existing macroinvertebrate community in the current context of the system, thereby reducing costs associated with active channel restoration. Monitoring future biological recovery and determining the contribution of changing assemblages to specific ecological processes would provide a critical underpinning for adaptive management and ecologically-effective restoration.