Revealing the Diet of Generalist Insect Predators in Strawberry Fields: Not Only Pests, But Other Predators Beware.

Generalist invertebrate predators contribute to pest management in agriculture, providing an important ecosystem service, particularly in organically managed fields. DNA-based methods to study food webs and feeding interactions in unrestricted field conditions have transformed dietary analysis of generalist predators. In this study, we used MiSeq next-generation sequencing (NGS) technology and universal arthropod primers to investigate the diet of several generalist insect predators collected in commercial organic Florida strawberry fields from November 2017 to March 2018. Of 12 predator insect taxa, Geocoris spp. (Say) (Hemiptera: Geocoridae) was the most abundant early in the growing season (November) and was collected consistently until the end of the season (early March). DNA sequences from 105 predator samples were matched to 44 arthropod families, and of these, 17 were categorized as pest families, 10 as nonpest or nonpredator families, and 17 as predator families. Drosophilidae was the most detected pest family, and Dolichopodidae was the most detected predator family. Prey diversity differed among the predators. Chrysoperla spp. (Neuroptera: Chrysopidae) consumed more prey earlier in the season than did other predators, whereas the other predators consumed a greater diversity of other predators regardless of month. Our results showed a high amount of intraguild predation, but also that predators are contributing to pest suppression in organic strawberries and providing an important biological control service in Florida organic strawberries.

Effect of European Chafer Larvae (Coleoptera: Scarabaeidae) on Winter Wheat and Role of Neonicotinoid Seed Treatments in Their Management.

A critical density of four third-instar larvae per 900 cm2 for European chafer, Rhizotrogus (Amphimallon) majalis (Razoumowsky), in winter wheat, Triticum aestivum L., was derived from small-plot greenhouse and field experiments conducted under favorable crop growing conditions at several Ontario and Michigan locations from 2001-2003. On average, plant weight was decreased by 14% and plant stand by 11% between zero and four larvae per 900 cm2. In a commercial field under moisture stress, a yield loss of 35% occurred at a density of two third-instars per 900 cm2. In short-term greenhouse experiments, density-dependent mortality was evident, whereas low larval recovery in field experiments indicates a high level of overwintering mortality, regardless of larval density. Winter wheat seed treatments of neonicotinoid insecticides, clothianidin, imidacloprid, and thiamethoxam provided protection from damage by larvae, but the level of protection was inconsistent between greenhouse and field small plots, and there was no apparent difference in protection amongst active ingredients or between application rates. There was little evidence of larval mortality owing to seed treatment, which supports the suggestion that neonicotinoid insecticides protect seedlings from loss by a nonlethal mechanism. Overall, we estimate that a low rate of neonicotinoid insecticide used at larval densities just less than the critical density will mitigate winter wheat losses by 85%.

Ground and rove beetles (Coleoptera: Carabidae and Staphylinidae) are affected by mulches and weeds in highbush blueberries.

Biological control of insects by predators may be indirectly influenced by management practices that change the invertebrate community in agroecosystems. In this study we examined effects that mulching and weeding have on predatory beetles (Carabidae and Staphylinidae) and their potential prey in a highbush blueberry field. We compared beetle communities in unweeded control plots to those that were weeded and/or received a single application of compost or pine needle mulch. Compost mulch and weeding significantly affected the carabid community while the staphylinid community responded to compost and pine needle mulches. Effects because of mulch tended to intensify in the year after mulch application for both families. Estimates of species richness and diversity for Carabidae and Staphylinidae were similar in all plot types, but rarefaction curves suggested higher Carabidae richness in unmulched plots despite fewer individuals captured. Carnivorous Carabidae, dominated by Pterostichus melanarius, were most frequently captured in compost plots both years, and omnivores were most frequently captured in unweeded compost. Density of millipedes, the most abundant potential prey, was generally greater in mulched plots, whereas seasonal abundance of small earthworms varied among mulch types. Our results have potential implications for biological control in mulched highbush blueberries depending on beetle consumption rates for key pests and how rates are affected by alternative prey.

Emergence of blueberry maggot flies (Diptera: tephritidae) from mulches and soil at various depths.

Control of blueberry maggot, Rhagoletis mendax Curran, typically is achieved with insecticides targeting adult flies before females oviposit in ripening fruit. Management strategies targeting other life stages have received less attention. We tested effects of compost or pine needle mulches on emergence of blueberry maggot flies under laboratory and field conditions. Few flies emerged from pupae that were buried under 20 cm of pine needles in all experiments, but burial in 20 cm of compost did not always result in low fly emergence. Burial of pupae in 5 cm of compost or pine needles did not reduce fly emergence compared with 1 cm in soil. Low emergence with increased mulch depth appeared to be primarily because of failure of flies to ascend to the surface after they exited puparia. Low emergence also was associated with high moisture levels causing rotten, discolored pupae, particularly in the laboratory in compost. No flies emerged from pupae buried in 1 cm of pine needles in the field. In this case no flies exited puparia, likely because high temperatures (>30°C) at the surface killed pupae. Thus, mulch application under highbush blueberries (Vaccinium corymbosum L.) after maggots drop from berries can reduce emergence success of flies from buried pupae, but the level of control will depend on mulch depth and may vary with rainfall and temperature.

Control decision rule for European chafer (Coleoptera: Scarabaeidae) larvae in field corn.

After greenhouse and outdoor microplot experiments, a critical density of two third instars per microplot for third instars of European chafer, Rhizotrogus (Amphimallon) majalis (Razoumowsky), in corn, Zea mays L., was derived. On average, the number of missing or damaged plants increased approximately 8% from zero to two larvae per 900 cm2. Furthermore, 23 fields in 2 yr were sampled for larvae along transects by using a golf cup cutter as the sampling tool and the critical density of 0.2 larva per sampling unit as the critical density. The sampling unit was one golf cup cutter with a diameter of 10.8 cm or 91.4 cm2 (10 sampling units approximately 900 cm2 approximately 1 foot2). Fieldwide means and variation were modeled to Taylor's power law, a = 1.42 and b = 1.47, and 20 of 23 fields fit the negative binomial probability distribution. Wald's formula for a sequential sampling plan was most accurate and least time-consuming, according to the operating characteristic and the average sample number function, relative to Iwao's and converging lines formulae. Percentage of sand, topography, soil bulk density, and proximity to trees were measured as potential predictors of areas with high larval density. Percentage of sand and soil bulk density were significant predictors, and topography and proximity to trees were not significant predictors. Field areas where the percentage of sand is high and the soil bulk density is low to moderate or where the percentage of sand is moderate and the soil bulk density is low should be chosen as sampling locations.

The effect of pH on heat denaturation and gel forming properties of soy proteins.

This study is focussed on the influence of pH on the gel forming properties of soy protein isolate and purified glycinin in relation to denaturation and aggregation. At pH 7.6 more fine-stranded gels were formed characterised by low G' values, and a smooth, slightly turbid appearance, whereas at pH 3.8 coarse gels were obtained with a high stiffness and a granulated, white appearance. Low G' values, as found at pH 7.6, correlate with a high solubility of glycinin and soy protein isolate (ca. 50%) after heating at low protein concentration. At pH 3.8 all protein precipitated upon heating, which correlates with relatively high G' values. The role of beta-conglycinin during gelation of SPI seems to be minor at pH 7.6, which is indicated by the fact that, in contrast to pH 3.8, notable gel formation did not start upon heat denaturation of beta-conglycinin. Furthermore, the mechanism of gel formation seems to be affected by pH, because at pH 7.6, in contrast to pH 3.8, the disulphide bridge between the acidic and the basic polypeptide of glycinin is broken upon heating.