Submitted to: Southwestern Entomologist
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/10/2006
Publication Date: 12/1/2006
Citation: Behle, R.W., Garcia-Gutierrez, C., Tamez-Guerra, P., Mcguire, M.R., Jackson, M.A. 2006. Pathogenicity of blastospores and conidia of Paecilomyces fumosoroseus against larvae of the mexican bean beetle, Epilachna varivestis mulsant. Southwestern Entomologist. 31(4):289-295. Interpretive Summary: Pest management requires continual searches for new control tactics to combat the development of pesticide resistance and reduce chemical pesticide load in crop production environments. Many fungi are known to provide effective biological contol of insect pests. However, the specific pest control combinations must be tested to demonstrate the potential for particular fungal agents to infect specific target insect pests. In this case, the fungus known as Pfr (Paecilomyces fumosoroseus) was tested for activity against the Mexican bean beetle, an important pest of beans and soybeans throughout much of North America. Two fungal spore types produced by alternative methods both caused infection and death of the target insects. This report opens the door for further research by government and industry scientists to determine the potential for development of this fungus as a biological pesticide.
Technical Abstract: The effects of blastospores and conidia of Paecilomyces fumosoroseus were compared using dipped leaf and topical application bioassay techniques against 3-day-old larvae of Mexican bean beetle (MBB), Epilachna varivestis Mulsant. Blastospores of P. fumosoroseus were produced using strain ARSEF 3581 grown in a liquid basal medium, whereas conidia were produced on potato dextrose agar (PDA). Initial insecticidal activity was demonstrated with a single dosage dipped-leaf assay with MBB larvae using a concentration of 1 x 10(8) conidia or blastospores/mL. Blastospores, conidia, and no fungus control treatments averaged 90%, 86%, and 19% larval mortality, respectively, after 3 days continuous exposure. Subsequently, a dosage response assay was completed to compare two assay conditions. Five spore concentrations, 1.2 x 10(9), 2.4 x 10(8), 4.8 x 10(7), 9.6 x 10(6), and 1.9 X 10(6) spores/mL, were prepared and used for both assay techniques. For the dipped-leaf technique, 25 larvae were exposed to treated leaf disks, 5 larvae to each of 5 treated leaf disks per spore concentration. For the topical assay, 5 uL was applied directly to each of 25 larvae for each spore concentration. After 3 days incubation, blastospores of P. fumosoroseus showed higher activity than conidia; and the topical application technique was more effective (lower LC(50) values and lower X(2) values) than the dipped leaf assay technique. This research demonstrates the insecticidal activity of P. fumosoroseus on MBB and provides a comparison of two basic bioassay techniques that may be useful in future research on this topic.