Progress towards a multi-species lure: comparison of behavioural bioassay methods for multi-species attractants against three pests of stored grain

The object of the study reported here was to establish the best behavioural bioassay to ascertain the responses of three representative species of stored-grain insect pests to potentially attractive odours. The insects tested were Oryzaephilus surinamensis, Sitophilus granarius and Cryptolestes ferrugineus. Following consideration of different types of behavioural bioassay, the Y-tube olfactometer and the pitfall bioassay were chosen for comparison. Both were tested with a representative substance known to be attractive to the test species: carob (Ceratonia siliqua) aeration extract in pentane, and a pentane control. A number of physical and biological factors were taken into account in order to ascertain the most efficient bioassay method while retaining similarity to the natural environment of the insects. The Y-tube olfactometer was used with these species for the first time and it gave good differentiation between test and control with O. surinamensis and S. granarius but not with C. ferrugineus. With the pitfall bioassay, the optimum conditions for screening potential attractants for all three species were 20°C and 50% relative humidity, with a bioassay duration of 1 h. Therefore, the optimum bioassay method for mixed sex adults of the three species tested was the pitfall bioassay. The increased response to the attractant with increased temperature (from 15°C to 20°C) shows that changing temperature may affect the insects’ responses.