Host Selection Behavior Of Helicoverpa Armigera(Hübner) Under The Odor Environment Of Multiple Host Plants

To elucidate the effect of plant diversity on herbivoral host selection, enrich the related theories of biodiversity and herbivore-plant co-evolution, and provide a scientific accordance for the application of intercropping and the development of ecological controlling of insect pests, the author systemically studied the ovipositional and feeding responses of a generalist, Helicoverpa armigera, to the volatiles of six host plant species as tobacco, cotton, tomato, hot pepper, peanut, and maize, as well as their different combinations in the laboratory, and the tested stages included adults, newly-hatched larvae, and fourth instar larvae. The main results are summarized as follows:(1) All the ovipositing females exhibited significant ovipositional preference to the volatiles derived from the six host species when each paired with clean air, suggesting that all the test plants were the preferred oviposition hosts for this generalist. H. armigera females preferred to tobacco volatiles in a dual choice bioassay when each tobacco plant was paired with the other five host plants, suggesting tobacco was the most preferred host for H. armigera. When multiple combinations of the other five host plants were added to the environment of tobacco, and paired with tobacco, we found that the combinations of peanut, hot pepper, and maize, mixed in binary or ternary combinations, showed fairly strong interferences to the choice response of H. armigera to the most preferred host species, e.g. tobacco, but the quartery combinations or higher-level combinations did not exhibit remarkable interferences, suggesting that a threshold of host diversity assessing may present in the selection of most preferred host species from a complex of host species.(2) The newly-hatched larvae exhibited fairly strong approaching response to the volatiles emitted from the six host plants when each was paired with clean air, in accordance with the choice of the adults. The new-borns preferred to tobacco leaf volatiles in a dual choice bioassay when each tobacco leaf disc was paired with the other five host plant leaf discs in the same size, or in a multiple choice bioassay when all the leaf discs from the six plants were presented together, this was in accordance with adult choice again. Peanut volatiles could mask the tobacco volatiles, while the addition of cotton volatiles to tobacco volatiles showed stronger attractiveness to the new-borns than the paired pure tobacco volatiles, suggesting that different combinations of plants, even the combinations of host plant species, could interfere the approaching response of the new-borns, which could be considered as “naive” for they were tested without any host plant experience.(3) The fourth instar larvae showed different feeding preference to different host leaf discs when tobacco leaf discs were paired with the other five host leaf discs, among them tobacco, cotton, and peanut leaf discs were feeding more than those of maize, hot pepper, and tomato, in accordance with natural feeding preference order of the late instars, but the reaction speeds had not significant difference in a dual choice bioassay when tobacco were paired with the other hosts, or the orthogonal combinations of the other five host species were added to tobacco paired with tobacco alone, suggesting that olfactory played a secondary role in the host selection of the late instars.All together, the adult is the key host selection stage, and olfactory plays a primary role during this process, and the new-born offspring may compensate the ovipositional decision of their mother depend on olfactory in a fairly short distance, but the late instars may choose their preferred host mainly depend on gustory system. Therefore, the regulation of oviposition choice should be considered as a emphasis in the design of intercropping system intending to control the generalist pests via host plant diversity.