The Western Flower Thrips (WFT), Franklinella occidentalis, causes significant economic losses in glasshouse crops via feeding damage and virus transmission. The ability to rapidly develop resistance to pesticides makes it an excellent candidate for alternative methods of management. One promising alternative for thrips management in glasshouses is the entomopathogenic fungus, Beauveria bassiana.
In commercial production, there is ambiguity as to the efficacy of B. bassiana products against WFT. To better understand the pathogen-insect interaction, some fundamental questions need to be addressed. How do thrips, which are highly cryptic, acquire a lethal dose of conidia? Where are conidia located on the insect’s body? Are doses acquired on certain body parts better correlated with mortality than those on other parts?
To begin answering these questions, a series of laboratory experiments were conducted using two commercially available formulations of B. bassiana strain GHA, BotaniGard ES and BotaniGard 22WP, and an unformulated technical powder, all of which were provided by the Mycotech Corporation (Butte, Montana). An efficient bioassay was developed and B. bassiana was found to be highly virulent against thrips (LC50 of=20 conidia/mm2). This result was used to determine an experimental range of five doses. Second instar WFT were allowed to feed for 24 h on leaves treated with conidia. The total number and location of conidia on each insect was determined by light microscopy and correlated with percent infection.
To compare the laboratory results with results under commercial conditions, a series of greenhouse experiments were performed. Impatiens plants, which were infested with all stages of WFT, were sprayed with BotaniGard 22WP. After 24 h WFT were then sampled and the number of conidia acquired by second instar and adult life stages were determined by light microscopy and correlated with percent infection.
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA