Olive fruit volatiles route intraspecific interactions and chemotaxis in Bactrocera oleae (Rossi) (Diptera: Tephritidae) females.

Plant nutritional quality and chemical characteristics may affect the fitness of phytophagous insects. Here, the olfactory preferences of Bactrocera oleae (Rossi) females toward olives with different maturation and infestation status were evaluated in three cultivars: Ottobratica, Roggianella and Sinopolese. Volatile profiles from olives were identified by SPME/GC-MS. Choice tests were performed to determine the responses of B. oleae adult females toward fruits and pure chemicals linked to infestation degree. Cultivar was the main source of variability explaining the differences recorded in volatile emissions. Moreover, three VOCs [ß-myrcene, limonene and (E)-ß-ocimene] were associated to infestation status across all olive varieties. In choice-tests, B. oleae females always preferred the olfactory cues from low-infested over high-infested fruits. Therefore, choice-tests using synthetic VOCs, emitted in greater amount by high-infested fruit, were arranged in order to identify putative B. oleae kairomones. While females were indifferent to ß-myrcene, the highest dosages of limonene and (E)-ß-ocimene were unfavoured by the tested flies, which preferentially moved toward the empty arm of the Y-tube. Furthermore, females preferred the lowest concentration of ß-ocimene compared to the highest one. These results supported our hypothesis that fruit VOCs may serve as kairomones for female flies.

VOC emissions influence intra- and interspecific interactions among stored-product Coleoptera in paddy rice.

Olfaction is a pivotal sense for insects and granivorous pests may exploit grain volatiles for food selection. Tribolium confusum, is a secondary pest of stored cereals that benefits from primary pests' infestation, as other secondary feeders, triggering competition. This study aimed to evaluate the preferences of T. confusum females toward different-infested paddy rice, highlighting the impact of intra- and interspecific competition. Tribolium confusum showed positive chemotaxis toward rice infested by larvae of a primary pest (Sitophilus zeamais), but not for grain attacked by adults alone. Furthermore, kernels concurrently infested by a primary (S. zeamais) and a secondary pest (T. confusum or Cryptolestes ferrugineus) were evaluated in Y-tube bioassays, highlighting that both food-sources were innately attractive for T. confusum females. Moreover, females positively oriented toward rice infested by conspecifics, while they avoided grain infested by C. ferrugineus, averting an extremely competitive habitat. Behavioural responses of T. confusum females and volatile emissions of different-infested rice highlighted the occurrence of plant-mediated interactions among insects from the same trophic guild. Seventy volatiles were identified and significant differences among the tested food-sources were recorded, emphasizing the presence of 6 putative attractants and 6 repellents, which may be useful biocontrol tools.