Quantitative study of aphid natural enemies in central Oklahoma canola fields

Authors: Elliott, Norman - Norm; GILES, KRISTOPHER - Oklahoma State University; BAUM, KRISTEN - Oklahoma State University; ELSAY, SARAH - Oklahoma State University

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2021
Publication Date: 12/15/2022
Citation: Elliott, N.C., Giles, K.L., Baum, K.A., Elsay, S.M. 2022. Quantitative study of aphid natural enemies in central Oklahoma canola fields. Southwestern Entomologist. 47(4):821-828. https://doi.org/10.3958/059.047.0403.
DOI: https://doi.org/10.3958/059.047.0403

Interpretive Summary: Winter canola is a rotational winter crop with wheat grown for its oil and to facilitate control of weedy cool season grasses in fields used for frequently for wheat production in Oklahoma. Canola is typically planted in late September through October in central Oklahoma and harvested in June. Three aphid species typically infest canola fields in central Oklahoma, the cabbage aphid, green peach aphid, and turnip aphid. Predatory insects and spiders known to prey on aphids are present in canola fields. In addition, hymenopteran parasitoids of aphids are present in canola fields in central Oklahoma. In this study we sampled a total of 22 canola fields in central Oklahoma during three canola growing seasons. The parasitoid Diaeretiella rapae was the most abundant parasitoid in canola fields whereas spiders were the most abundant predator. Several other predator taxa were encountered in samples. Abundance of most species increased from fall to spring. The density od Diaeretiella rapae and larval lady bird beetles showed a numerical response to aphids in canola indicating a strong linkage in the population dynamics of these two natural enemies with that of the aphids. In spite of the many unknowns regarding the nature of interspecies interactions among natural enemies in canola it is likely that the combined contributions of the aphid specialist natural enemies, D. rapae and several species of lady bird beetle, and perhaps spiders, which are general predators on a broad range of arthropods, exert the greatest impact on aphid infestations in canola fields in central Oklahoma. This study lays the groundwork for more detailed investigations of biological control by natural enemies of aphids in canola.

Technical Abstract: Winter canola (Brassica napus L.) is a rotational winter crop with wheat (Triticum aestivum L) in Oklahoma. Canola is typically planted in late September through October in central Oklahoma and harvested in June. Three aphid species typically infest canola fields in central Oklahoma, the cabbage aphid, Brevicoryne brassicae L., green peach aphid, Myzus persicae (Sulzer), and turnip aphid, Lipaphis pseudobrassicae (Davis). Predatory insects and spiders known to prey on aphids are present in canola fields. In addition, hymenopteran parasitoids of aphids are present in canola fields in central Oklahoma. In this study we sampled a total of 22 canola fields in central Oklahoma during three canola growing seasons. Six fields were sampled in the 2016-2017 growing season and eight fields were sampled in each of the 2017-2018 and 2018-2019 growing seasons. We sampled aphid natural enemies and aphids in canola fields using a D-vac suction sampler in early November and again in mid-March. During the three canola growing seasons aphids in canola ranged from 2.38 to 50.86 aphids per 120 placements of the D-vac sampling head. The parasitoid Diaeretiella rapae (McIntosh) was the most abundant parasitoid ranging from 0.04 to 5.13 per 120 placements among growing seasons, whereas Araneae (spiders) were the most abundant predator ranging from 0.35 to 4.88 per 120 placements among growing seasons. Several other predator taxa were encountered in samples including Chrysopidae, Hemerobiidae, Nabidae, and Syrphidae. Abundance of most species increased from November to March. Correlations of abundance of D. rapae and larval Coccinellidae to aphid abundance were positive and significant suggesting that these species exhibited a numerical response to aphids in canola. In spite of the many unknowns regarding the nature of interspecies interactions among natural enemies in canola it is likely that the combined contributions of the aphid specialist natural enemies, D. rapae and several species of Coccinellidae, and perhaps spiders, which are general predators on a broad range of arthropods, exert the greatest impact on aphid infestations in canola fields in central Oklahoma.