Inter-specific relationship among stored-product Coleoptera: role of VOC emissions

Volatile Organic Compounds (VOCs) play a pivotal role routing food and host selection in insects. Among Coloptera, stored-product pests may exploit volatile emissions to discriminate and select trophic sources presenting different palatability values. Here, we focused the attractiveness of food sources toward an external feeder of kernels, Tribolium confusum J. du Val, which is generally a secondary pest of grains. Thus, the presence of previous infestation of primary pests, such as Sitophilus zeamais Motschulsky, enhances T. confusum population as well as other secondary feeders. The present study aimed to evaluate under laboratory conditions the preferences of T. confusum females toward differentially infested rice, highlighting the impact of intra- and inter-specific competition. Tested beetles positive oriented toward S. zeamais-infested rice in choice bioassays and preferred this source over intact rice. Furthermore, to assess the effect of intra- and inter-specific competition, kernels concurrently infested by a primary (S. zeamais) and a secondary pest [T. confusum or Cryptolestes ferrugineus (Stephens)] were tested in no-choice bioassays, highlighting that both food sources were innately attractive for T. confusum females. Nevertheless, the presence of a secondary infestation greatly altered T. confusum responses in choice bioassays. Indeed, when a conspecific infestation occurs, females showed positive chemotaxis toward the double-infested rice, while they avoided the rice infested by C. ferrugineus, averting a far more competitive habitat. T. confusum behavioral responses were in agreement with VOC analyses, which identified 70 volatiles and emphasized significant differences among the tested food sources, highlighting the presence of putative attractive and repellent compounds.