High-throughput molecular gut content analysis of aphids identifies plants relevant for potato virus Y epidemiology.

Aphids are phloem-feeding insects that reduce crop productivity due to feeding and transmission of plant viruses. When aphids disperse across the landscape to colonize new host plants, they will often probe on a wide variety of nonhost plants before settling on a host suitable for feeding and reproduction. There is limited understanding of the diversity of plants that aphids probe on within a landscape, and characterizing this diversity can help us better understand host use patterns of aphids. Here, we used gut content analysis (GCA) to identify plant genera that were probed by aphid vectors of potato virus Y (PVY). Aphids were trapped weekly near potato fields during the growing seasons of 2020 and 2021 in San Luis Valley in Colorado. High-throughput sequencing of plant barcoding genes, trnF and ITS2, from 200 individual alate (i.e., winged) aphids representing nine vector species of PVY was performed using the PacBio sequencing platform, and sequences were identified to genus using NCBI BLASTn. We found that 34.7% of aphids probed upon presumed PVY host plants and that two of the most frequently detected plant genera, Solanum and Brassica, represent important crops and weeds within the study region. We found that 75% of aphids frequently probed upon PVY nonhosts including many species that are outside of their reported host ranges. Additionally, 19% of aphids probed upon more than one plant species. This study provides the first evidence from high-throughput molecular GCA of aphids and reveals host use patterns that are relevant for PVY epidemiology.

Dietary history of click beetles and wireworms in the genus Limonius (Coleoptera: Elateridae) revealed by molecular gut content analysis.

Wireworms, the larval stage of pest click beetle species (Coleoptera: Elateridae), are pests of many crops in North America including root vegetables and cereals. There is cause for concern amongst growers who are facing pressure from wireworms because there are a decreasing number of effective pesticides that can be used for wireworm management. Most research on pest elaterids has focused on the wireworm stage, which is the damage causing life stage. Recently, the focus in elaterid research has shifted to the adult click beetle stage, including identification of semiochemicals and development of effective traps. However, there is still a lot to be discovered about the basic biology of click beetles, including their feeding ecology. In an effort to understand the feeding ecology of click beetles, we investigated the presence of plant DNA in the digestive tracts of Limonius californicus (Mann.), L. canus (LeConte), and L. infuscatus (Mots.) beetles collected in 3 different locations within central Washington. To examine dietary histories of beetles and wireworms, specimens were collected from natural habitats and high-throughput sequencing of the plant genes trnF and ITS was used to identify their dietary history. Results revealed that click beetles do feed on a large variety of plants, which included a large quantity of brassicaceous plants commonly found in areas surrounding wireworm infested plots. The identification of the dietary history of the click beetles allowed us to infer their landscape-scale movements thus providing a means to better understand their behavior.

Effect of temperature on long-term storage of codling moth granulovirus formulations.

Codling moth, Cydia pomonella (L.), is the major pest of apple (Malus spp.) in the western United States and many other regions of the world. The codling moth granulovirus (CpGV) provides a selective and safe means of its control. We assessed the long-term stability and storage potential of two commercial formulations of CpGV, Cyd-X, and Virosoft. All assays were performed with individual C. pomonella neonate larvae in 2-ml vials on 1 ml of artificial larval diet that was surface inoculated with 10 microl of the test virus suspension. Baseline quantitative assays for the two formulations revealed that the LC50 and LC95 values (occlusion bodies per vial) did not differ significantly between the formulations. For year-long studies on Cyd-X stability, the product was stored at -20, 2, 25, and 35 degrees C, and quantitative bioassays were conducted after 0, 3, 6, and 12 mo of storage. Cyd-X retained good larvicidal activity from -20 to 25 degrees C, and it was the least negatively affected at the lowest temperature. Storage of Cyd-X at 35 degrees C was detrimental to its larvicidal activity within 3 mo of storage. For longer term storage studies, Cyd-X and Virosoft formulations were stored at 2, 25, and 35 degrees C, and assayed for larvicidal activity over a 3-yr period. For recently produced product, a 10-microl sample of a 10(-5) dilution of both formulations resulted in 95-100% mortality in neonate larvae. Larvicidal activity for the Cyd-X formulation remained essentially unaffected for 156 wk when stored at 2 and 25 degrees C, but it began to decline significantly after 20 wk of storage at 35 degrees C. The Virosoft formulation stored at 2 degrees C also remained active throughout the 3-yr study, but it began to decline in larvicidal activity after 144 wk at 25 degrees C and 40 wk at 35 degrees C. The information reported in this study should be useful to growers and commercial suppliers for avoiding decreases in CpGV potency due to improper storage conditions.

Factors affecting entomopathogenic nematodes (Steinernematidae) for control of overwintering codling moth (Lepidoptera: Tortricidae) in fruit bins.

Fruit bins infested with diapausing codling moth larvae, Cydia pomonella (L.), are a potential source of reinfestation of orchards and may jeopardize the success of mating disruption programs and other control strategies. Entomopathogenic nematodes (EPNs) were tested as a potential means of control that could be applied at the time bins are submerged in dump tanks. Diapausing cocooned codling moth larvae in miniature fruit bins were highly susceptible to infective juveniles (IJs) of Steinernema carpocapsae (Weiser) and Steinernema feltiae (Filipjev) in a series of experiments. Cocooned larvae are significantly more susceptible to infection than are pupae. Experimental treatment of bins in suspensions of laboratory produced S. feltiae ranging from 10 to 100 IJs/ml of water with wetting agent (Silwet L77) resulted in 51-92% mortality. The use of adjuvants to increase penetration of hibernacula and retard desiccation of S. feltiae in fruit bins resulted in improved efficacy. The combination of a wetting agent (Silwet L77) and humectant (Stockosorb) with 10 S. feltiae IJs/ml in low and high humidity resulted in 92-95% mortality of cocooned codling moth larvae versus 46-57% mortality at the same IJ concentration without adjuvants. Immersion of infested bins in suspensions of commercially produced nematodes ranging from 10 to 50 IJs/ml water with wetting agent in an experimental packing line resulted in mortality in cocooned codling moth larvae of 45-87 and 56 - 85% for S. feltiae and S. carpocapsae, respectively. Our results indicate that EPNs provide an alternative nonchemical means of control that could be applied at the time bins are submerged in dump tanks at the packing house for flotation of fruit.

Interactions of two idiobiont parasitoids (Hymenoptera: Ichneumonidae) of codling moth (Lepidoptera: Tortricidae) with the entomopathogenic nematode Steinernema carpocapsae (Rhabditida: Steinernematidae).

Simultaneous use of parasitoids and entomopathogenic nematodes for codling moth (CM) control could produce an antagonistic interaction between the two groups resulting in death of the parasitoid larvae. Two ectoparasitic ichneumonid species, Mastrus ridibundus and Liotryphon caudatus, imported for classical biological control of cocooned CM larvae were studied regarding their interactions with Steinernema carpocapsae. Exposure of M. ridibundus and L. caudatus developing larvae to infective juveniles (IJs) of S. carpocapsae (10 IJs/cm2; approximately LC(80-90) for CM larvae) within CM cocoons resulted in 70.7 and 85.2% mortality, respectively. However, diapausing full grown parasitoid larvae were almost completely protected from nematode penetration within their own tightly woven cocoons. M. ridibundus and L. caudatus females were able to detect and avoid ovipositing on nematode-infected cocooned CM moth larvae as early as 12h after treatment of the host with IJs. When given the choice between cardboard substrates containing untreated cocooned CM larvae and those treated with an approximate LC95 of S. carpocapsae IJs (25 IJs/cm2) 12, 24, or 48h earlier, ovipositing parasitoids demonstrated a significant preference for untreated larvae. The ability of these parasitoids to avoid nematode-treated larvae and to seek out and kill cocooned CM larvae that survive nematode treatments enhances the complementarity of entomopathogenic nematodes and M. ridibundus and L. caudatus.