Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2005
Publication Date: 5/1/2006
Citation: Ugine, T.A., Wraight, S.P., Sanderson, J.P. 2006. The influence of impatiens pollen availability and exposure to beauveria bassiana on bionomics of western flower thrips frankliniella occidentalis (thysanoptera: thripidae). Environmental Entomology. 37:186-195.
Interpretive Summary: Western flower thrips (WFT) is one of the most important insect pests of greenhouse floriculture. This insect has demonstrated a strong capacity to resist chemical insecticides, and alternative control agents are needed for development of sustainable pest management systems. The fungal pathogen Beauveria bassiana is registered in the U.S. for biological control of thrips, and we have recently investigated its potential to control WFT infesting garden impatiens, one of the most important bedding crops in the northeastern U.S. Our studies have revealed that although B. bassiana was highly virulent against WFT in laboratory bioassays, it was ineffective in greenhouse tests. This study was conducted to identify characteristics of the fungus and attributes of the insect host and the insect host plant that limit pest control efficacy. Because pollen is an important nutrient source for thrips and is well known to enhance thrips reproduction, bioassays were conducted in which adult WFT were exposed to a high rate of B. bassiana spores on impatiens leaves supplemented or not supplemented with impatiens pollen. Fungal infection reduced total offspring production by only 56%. Control was limited because the fungus was slow to kill, and infected thrips produced offspring at normal rates until death. Pollen had no negative effects on B. bassiana infection, but stimulated an overall 2-3 fold increase in thrips reproduction. These results suggest that if B. bassiana is to be used successfully as a thrips management tool in impatiens crops, it must be applied before pollen becomes present, and it must be targeted against thrips immature stages to kill the insects before they reach reproductive maturity.
Technical Abstract: Adult female western flower thrips, Frankliniella occidentalis (Pergande), were exposed for 24 h to impatiens leaf disks treated with Beauveria bassiana at two application rates (117 and 1017 viable conidia/mm2) and subsequently maintained on impatiens leaf disks supplemented or not supplemented with impatiens pollen. Offspring production and mortality of insects was monitored daily. Exposure to B. bassiana at the low and high rates significantly reduced thrips longevity by 4.1 and 4.8 days, reduced the ovipositional period by 3.4 and 4.6 days, and reduced lifetime fecundity by 25 and 56% at the low and high rates, respectively. Infection by B. bassiana resulted in no sublethal (pre-mortem) effects on offspring production, even on the day before death. Pollen supplements had no effect on adult female thrips longevity, yet did significantly increase both daily (2.5 and 2.8 times) and lifetime fecundity (2.2 and 2.9 times) compared to control insects in test at the low and high rates, respectively. No significant Beauveria x pollen interactions were detected. The increase in both daily and lifetime offspring production in the presence of pollen and the slow action of B. bassiana suggest that if B. bassiana is to be used successfully as a thrips management tool in impatiens crops, it must be applied before pollen becomes present and targeted against thrips immature stages to kill the insects before they reach reproductive maturity.