Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/5/2004
Publication Date: 6/1/2004
Citation: Leland, J.E., Mcguire, M.R. 2004. Strain selection of a fungal entomopathogen, beauveria bassiana, for control of plant bugs (lygus spp.). National Cotton Council Beltwide Cotton Conference. Interpretive Summary: A fungus that kills insects is naturally found in populations of an important cotton insect pest, tarnished plant bug (TPB), and is being considered as an option for controlling this pest. This fungus was much less prevalent in TPB populations from Mississippi than in populations of western tarnished plant bug (WTPB) from California. Fungal collections from the TPB and WTPB were studied for characteristics important to their use in controlling these insect pests. These included; spore production, ability to kill the two insect pests at 25°C and 35°C, potential for killing beneficial insects, and survival of the fungus in sunlight. Many of the fungi collected were ten times better at killing the two pests at 25°C than a fungus that is now commercially-available. Although the fungi collected grew at 35°C, they did not kill many of the insects. When a large amount of the fungus was applied to certain beneficial insects it did not kill many of the ladybugs, immature lacewings, or immature pirate bugs, but it did prevent some of the lacewings from reaching adulthood and killed a large percentage of adult pirate bugs. Some of the fungal collections from WTPB survived longer in sunlight than the commercial fungus. Further work will determine the potential for using this fungus for controlling TPB and WTPB and potential impacts on beneficial insects in the field.
Technical Abstract: Surveys of natural Beauveria bassiana infection levels in tarnished plant bug (Lygus lineolaris) populations from the delta and hill country regions of Mississippi were conducted. Natural infection levels in L. lineolaris were significantly lower than those observed in L. hesperus populations from the San Joaquin Valley (SJV), CA in previous surveys. Infection levels in L. hesperus ranged from 0 to50% with an overall average of approximately 10%, whereas overall percentage infection in natural L. lineolaris populations was less than 0.3% with the highest infection level from a site being 8%. There was a trend toward higher infection levels occurring later in the both surveys, which were conducted from May through November, with nearly all isolates from L. lineolaris being collected in mid August through mid October. Isolates from L. hesperus were highly variable with regards to pathogenicity to L. hesperus and growth temperature optima. Seven isolates from L. hesperus and L. lineolaris that were more pathogenic than the commercial B. bassiana isolate (GHA) and able to grow at 35°C were selected for further evaluation of characteristics relevant to mycoinsecticide development. These characteristics included spore production, growth at 35°C, pathogenicity at 35°C, pathogenicity to select beneficial insects, and survival under solar radiation. Six of the seven isolates were prolific sporulaters producing spore concentrations equal to or greater than the GHA isolate. Although the seven isolates were able to grow at 35°C at a reduced rate, they had very low pathogenicity to L. lineolaris at this temperature. Thus far, bioassays against beneficial insects have only been conducted with isolates from L. lineolaris and the GHA isolate. Pathogenicity was low to ladybugs (Hippodamia convergens), lacewing larvae (Chrysopa carnea), and pirate bug (Orius insidiosis) nymphs. However, only approximately 30% of lacewing larvae treated with high spore concentrations that formed pupae emerged as adults and sporulation was observed in pupa (vs. 90% control emergence). Pathogenicity to O. insidiosus adults was high, similar to that observed in L. lineolaris adult bioassays. The isolates selected from L. hesperus survived longer under exposure to simulated solar radiation than the GHA isolate, whereas survival of isolates from L. lineolaris was similar to the GHA isolate. Two to four isolates will be selected from these characteristics for scaled-up spore production sufficient to conduct field trials against L. lineolaris in wild host plants and L. hesperus in alfalfa, and further bioassays against beneficial insects.