Phosphine Resistance in Thai Local Strains of Tribolium castaneum (Herbst) and Their Response to Synthetic Pheromone
Tribolium castaneum (Herbst), one of the key pests of stored grains worldwide, has been reported to develop resistance to fumigants in several countries. This research was focused on assessing the toxicity of phosphine against two local strains of T. castaneum from Thailand by comparison with the standard susceptible strain (QTC-4) from Australia and evaluating the response of the selected strain to synthetic pheromone. By bioassay under laboratory conditions, it was found that T. castaneum collected from an animal feed mill in Samut Prakan province (SP strain) exhibited resistance to phosphine with resistance ratios of 3–25.8 while the strain from Khon Kaen province (KK strain) showed a much lower resistance level with resistance ratios of 1–1.45. The SP and KK strains were then observed for their responses to the pheromone in an arena of 1 m3 in a glass cage. The results showed that synthetic pheromone could attract female beetles to the traps. Traps containing synthetic pheromone caught a significantly higher number of beetles than those of the untreated control. However, when comparing the response of the resistant strain (SP) with that of the susceptible strain (KK), it was found that both pheromone traps and untreated traps caught significantly lower numbers of resistant females than the susceptible ones. This may have been due to the resistant beetles being less active and wandering around less than the susceptible beetles. The lower response of resistant beetles to pheromone suggested that there is a need to find other alternatives for a monitoring system in areas where resistant populations occur in order to be able to make proper pest management decisions.