Infestation of maize cobs by Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae)—Aspects of biology and control

Abstract

Listen

Translate article

The initial attack and subsequent development of Prostephanus truncatus on maize cobs, with husk intact, was investigated at 27°C and 40, 50 and 70% r.h. The beetles showed a strong tendency to attempt infestation by first boring into the maize cob cores although they eventually gained access to the grain via the apex of the cob by walking between the grain and husk. At 50 and 70% r.h., the rate of oviposition over the first 2 wk was particularly high, while at 40% r.h. the rate was more or less constant. Some F 1 generation completed their development within 32–39 days at 50 and 70% r.h. and within 39–46 days at 40% r.h. Under all three moisture conditions, adult dispersal from the cobs was first detected at the end of the sixth week. Estimates were made of the rate of increase of P. truncatus under each of the three moisture conditions. The population increased most rapidly at 70% r.h. and was at its peak between the eighth and twelfth weeks during which time grain damage and weight loss had effectively reached 100%. At 50% r.h., this stage was reached between the twelfth and sixteenth weeks while by this time at 40% r.h. the grain weight loss was only 40%. Two novel techniques were tested for protecting maize cobs from infestation by P. truncatus. The exposed ends of maize cob cores were dipped into permethrin, 0.1% w/v aqueous dispersion or 0.5% w/w dilute dust, or untreated cobs were kept with permethrin-treated expanded-polystyrene blocks which acted as alternative refuges. Such treatments were examined at two beetle population densities. Dipping of the maize core was particularly effective in the prevention of infestation at low population density. This technique should be the subject of a field trial and if successful will offer important advantages over currently recommended control procedures.