Submitted to: Journal of Agricultural and Urban Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2003
Publication Date: 10/15/2002
Citation: MCGUIRE, M.R. PREVALENCE AND DISTRIBUTION OF NATURALLY OCCURRING BEAUVERIA BASSIANA IN SAN JOAQUIN VALLEY POPULATIONS OF LYGUS HESPERUS.. JOURNAL OF AGRICULTURAL AND URBAN ENTOMOLOGY. 2002. Interpretive Summary: The Western tarnished plant bug (WTPB) is one of the more devastating pests of cotton production causing economic losses of $30 million per year. Currently, broad spectrum chemical insecticides are used to control this pest. Unfortunately, these pesticides may also reduce predators and parasites that keep other insects such as aphids under natural control. Elimination of the predators and parasites may lead to population increases of the other pest insects. In a search for other natural mortality factors of WTPB, we found a fungus that kills the bugs in the field. The purpose of this report is to document naturally occurring fungus in WTPB populations throughout the San Joaquin Valley of California. We found that the fungus occurs virtually everywhere we looked and causes deaths of up to 50% of the WTPB we collected. However, only approximately 10% of the WTPB we collected in any given sample was infected. We also monitored 9 fields of alfalfa very closely to determine if the level of fungus had an impact on WTPB populations. In our samples less than 10% of the insects were infected and few effects were observed relating to population dynamics of the WTPB. Future work will examine the potential of commercializing some of the fungal strains we collected during this study.
Technical Abstract: Lygus hesperus Knight is a particularly damaging pest of cotton and control methods rely on synthetic chemical pesticides. A brief survey in November 2000 revealed the presence of Beauveria bassiana (Balsamo) Vuillemin in L. hesperus populations. To determine the extent of B. bassiana prevalence, both geographically and seasonally, samples of L. hesperus were obtained several times through the spring, summer and fall of 2001 from six counties in the San Joaquin Valley. L. hesperus were held live to determine percentage infection. B. bassiana was found in all counties throughout the sampling period except for a spring sample in one county. Prevalence of B. bassiana ranged from 0% to 50% and no other pathogens or parasites were found. In addition, weekly samples were obtained from each of several alfalfa fields in Kern County, CA over a two year period. In 2001, six fields were sampled and in 2002, four fields were sampled. B. bassiana was present in all fields but at different levels. In 2001, significant differences existed with respect to prevalence of fungus and L. hesperus. Fields in their first year of production had lower levels of B. bassiana than fields in their second or third year of production. In 2002, these differences were not present. Linear regressions showed a positive but weak relationship between infection level and L. hesperus density in 2001 only. In 2002, a significant linear relationship existed between sample date and percentage infection suggesting a buildup of pathogen with time. These data suggest that B. bassiana is present throughout the San Joaquin Valley and exists in the environment even in the hottest part of summer where temperatures routinely exceed 40°C.