Behavioural responses of Tribolium confusum to rice kernels: role of intra-and inter-specific competition on VOC emissions and female chemotaxis

Olfaction is a key sense routing insect host selection and grain volatiles may enhance granivorous pest orientation. Tribolium confusum J. du Val, is a secondary pest of stored cereals that benefits from primary pest infestation. However, competition may play a role on chemotaxis, altering the attractiveness of host resources. Here different host sources were evaluated under laboratory conditions. Firstly, we tested the attractiveness of intact and Sitophilus zeamais Motschulsky-damaged rice kernels to T. confusum females. In nochoice assays females positively oriented toward both odour sources, while, in two-choice bioassays, they preferred S. zeamais-infested rice over intact one, regardless the presence of adult maize weevils.To assess the effect of intra- and inter-specific competition, we tested the attractiveness of kernels concurrently infested by a primary (S. zeamais) and a secondary pest [T. confusum or Cryptolestes ferrugineus (Stephens)]. T. confusum females were attracted by both double-infested rices in no-choice assays. However, intra-specific infestation determined positive chemotaxis of females in two-choice tests, while rice simultaneously infested by C. ferrugineus and S. zeamais was less attractive than S.zeamais-damaged one, thus allowing T. confusum to avoid a competitive host-habitat. Lastly, HS-SPME and GCMS analyses showed peculiar Voc profiles for every different infested rice, highlighting the presence of putative attractive and repellent chemicals.