The effect of temperature and exposure to Beauveria bassiana on tarnished plant bug Lygus lineolaris (Heteroptera: Miridae) population dynamics, and the broader implications of treating insects with entomopathogenic fungi over a range of temperatures

Tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois) (Heteroptera, Miridae) are a major pest of cotton in most cotton growing regions of the Southern US. Studies were conducted to investigate how temperature and Beauveria bassiana (Balsamo) Vuilllemin infection impacted L. lineolaris fecundity and longevity, with the goal of determining what temperatures optimized B. bassiana’s control potential. B. bassiana-treated adult females and controls were maintained at constant 18 °C, 21 °C, 25 °C, 30 °C or 32 °C. The number of eggs laid was determined daily until death. B. bassiana caused large reductions in the total number of eggs laid (45–76%) at all temperatures; however, there was no effect of infection on the daily rate of egg production. There was not a sub-lethal effect of infection on egg production on the last full day of life. Intrinsic rates of natural increase and population doubling times were marginally affected by treatment with B. bassiana; doubling times increased with treatment a mean of 3.5 days (range 0.5–7.7 days). There was a temperature dependent trend in the length of the preoviposition period and the days to death after treatment with B. bassiana. As temperature increased from 18 °C to 32 °C, the number of days to death converged on the preoviposition period. The maximum difference was observed at 18 °C (5.3 days different) compared to 30 °C and 32 °C (0.3 days). These results strongly suggested that treatment of tarnished plant bugs with B. bassiana should be performed when plant bugs are in diapause or when temperatures are cool to minimize reproduction during the disease incubation period.

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► Beauveria bassiana reduced Lygus lineolaris egg laying by 45–76% at temps between 18 °C and 32 °C.
► B. bassiana had little impact on life table parameters including rm, R0, DT, and GT.
► Days-to-death of treated bugs converged on the preoviposition period as temp increased.
► B. bassiana treatments should be performed against bugs in diapause or at cool temps.