The susceptibility of eucalyptus tortoise beetle (Paropsis charybdis stål) [Coleoptera: Chrysomelidae] to Beauveria bassiana (Balsamo) vuillemin

Abstract

The relative susceptibility of eucalyptus tortoise beetle (Paropsis charybdis Stål) [Coleoptera: Chrysomelidae] to Beauveria bassiana strains (F 235, F 238 and F 305) and BotaniGard™ (commercial preparation of B. bassiana) was determined under laboratory conditions by measuring mortality of larvae, pupae, and adults and by estimating LT50 values at two concentrations (105 and 107 spores/ml). All strains tested were capable of infecting P. charybdis stages causing different levels of mortality. Strain F 305 was a significantly (P < 0.05) better strain than others. First instar larvae were the most susceptible stage, while adults were significantly (P < 0.05) less susceptible than other developmental stages.

The effects of relative humidity and temperature on the mortality of P. charybdis first instars infected by B. bassiana were assessed. Infection of first instars by B. bassiana strain F 305 at the two concentrations tested occurred in all humidities tested (53%, 75.5%, 85%, 92.5%, and 100% RH) at 25°C. The most favourable temperatures for this strain to infect P. charybdis first ins tars occur between 25 - 30°C.

The effect of leaf substrate was assessed to investigate the residual and direct contact effects of B. bassiana to the target stage of P. charybdis. Strain F 305 appeared to be infective to both P. charybdis first instars, following foliar application, and pupae, following leaf litter application.