Project Number: 3072-22000-016-35-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 25, 2017
End Date: Jan 31, 2019
Objective 1: Determine host suitability and preference for sorghum feeding aphid species by the sugarcane aphid parasitoid Aphelinus nr. nigritus. Objective 2: Evaluate the effects of Aphelinus nr. nigritus and other natural enemies on population suppression of sugarcane aphid in grain sorghum fields.
Laboratory colonies of four aphid species that typically infest sorghum will be utilized in studies of host suitability. A laboratory colony of the parasitoid A. nr. nigritis will be established from individuals collected from sorghum fields in Oklahoma and/or Texas. Newly emerged (within 24 hours) mated female parasitoids from this colony will be used in the experiments. Individuals of each aphid species will be exposed to newly emerged A. nr. nigritis females. After 24 h the female parasitoid will be removed, and the caged plant will be returned to the growth chamber. All mummies (parasitized aphids) that form on a plant will be removed, placed in a plastic petri-dish and returned to the growth chamber. Mummies will be checked periodically to determine the number of adult parasitoids that emerge. Ten such replicates for each of the four aphid species will be established. We will determine whether A. nr. nigritis exhibits preference for parasitizing sugarcane aphid or the most suitable co-occurring cereal aphid in sorghum in the Southern Plains. Data resulting from suitability and preference experiments will be subjected to analysis of variance to determine whether differences in suitability or preference exist among aphid species in sorghum. Natural enemy exclusion experiments will be conducted in experimental grain sorghum plots in summer 2018. The experimental plantings will be made at two locations. Two sorghum varieties will be planted in replicated plots in a randomized block design at each location. One variety will be susceptible to sugarcane aphid, while the second variety will contain a moderate level of genetic resistance to sugarcane aphid. Three treatments will be initiated in sorghum plants when they are in the six leaf stage of development: 1) A fine mesh enclosure, which is fine enough to prevent all insects from entering the enclosure (complete exclusion); 2) A coarse mesh enclosure, which is coarse enough to permit entry of parasitoids but not predaceous coccinellids (ladybird beetles) or other aphid predators typically found in grain sorghum fields; and 3) the same coarse mesh enclosure, but with a 15 cm diameter hole cut in each side, which will allow access by aphid predatory insects. One replicate of each treatment will be positioned within each subplot. Each cage will be infested with 10 adult, greenhouse-reared sugarcane aphids. At the end of four weeks the foliage from within each cage will be cut and placed into a bag, labeled, and placed in an ice chest for transport to the laboratory. Aphid population growth for complete exclusion, parasitoid only, and predator and parasitoid cages will be compared among resistant and susceptible sorghum varieties using analysis of variance for a split plot experimental design.