Effect Of Helicoverpa Armigera Experiences On Feeding And Oviposition Behaviours

The author studied the effects of larval feeding experience and adult host-contacting experience of generalist Helicoverpa armigera (Hiibner) on subsequent choice feeding behaviour and ovipositional choice, respectively; then tested the interactions among four host-derived secondaiy metabolites as well as that between four non-host-derived feeding deterrents, piperine and sanshool, whose anti-feedding mechanism was elucidated. The main results are summed as follows:(1) I tested the larvae feeding behavior of H. armigera by means of forced host-switching (at two hour interval) and cross-coating of secondary metabolites (at natural concentrations) from four common host plant species of the larvae:tobacco, hot pepper, tomato, and cotton. The results show that, in all the cases, the dietary-mixing did not significantly increase the overall leaf consumption of the fourth instar larvae, moreover, some combinations inhibited feeding amounts and others had no effect, suggesting that nutritional compensation hypothesis could not explain the dietary mixing behavior of the larvae. Both tobacco leaf and its major secondaiy metabolite, nicotine hydrate, significantly inhibited the leaf consumption of all the other host species, while neither hot pepper leaf nor its secondary metabolite, (E)-capsaicin, showed effect on feeding amounts of all the other host species. Although tomato leaf in dietary-switching groups did not affect the consumptions of all the other three host leaves, α-tomatine showed significant feeding deterrence when coated on the leaf of hot pepper or cotton. The consumption of tobacco leaf discs increased in cotton-tobacco switching group compared with that in tobacco non-switching group, but the coating of (+)-gossypol on tobacco leaf discs decreased the feeding amounts. Cotton and hot pepper leaf showed no significant interactive effect, neither in force-switching bioassay nor in cross-coating bioassay.(2) I investigated the short-term effect of larval feeding experience type and induction time on feeding choice in the laboratory, and the long-term effect of field feeding experience. The result indicates that the naive group did not exhibit feeding preference between cotton leaf and tobacco leaf, while the group with 6 h feeding induction on tobacco leaf preferred tobacco to cotton significantly. However, the individuals with 3 h feeding induction on cotton leaf showed significant feeding preference on tobacco, not the experienced host plant (cotton). Tobacco leaf consumption of field collected tobacco-developed larvae was significantly more than those of all the other three host plants, while the cotton leaf consumption of the cotton-developed larvae was only significantly more than that of hot pepper.(3) Effect of feeding experience on olfactory-based approaching behaviour:the larvae with either tobacco feeding experience or hot pepper feeding experience approached to hot pepper more often than tobacco, but the naive group did not show any difference between tobacco and hot pepper. The group with tomato feeding experience approached to tomato more often than to cotton, but the cotton-experienced group and the naive group did not show any preference, suggesting that the re-shaped activity of tomato feeding experience to olfactory system was stronger than that of cotton. The naive group and the tomato-experienced group significantly preferred tomato to tobacco, but tobacco feeding experience could weaken this preference remarkably, so does cotton feeding experience under the dual choice condition of cotton paired with tobacco.(4)Effect of adult host-contacting experience on subsequent oviposition beahviour:H. armigera mated females showed innate oviposition preference to tobacco leaves, and tobacco-contacting experience group showed similar trend, while after conacted with the other three host plants, the oviposition preference to tobacco was disappeared, suggesting that adult experience could also re-shape ovipositional behaviour, but the innate preference could only be masked but not be reversed.(5) I studied the action mechanism of two non-host-derived feeding deterrents, piperine and sanshool, then tested the effect of previous feeding experience of the two compounds, treated alone or combined, on the subsequent choice feeding response. Both the two substances were deterred feeding via post-ingestive gustatory mechanism. Gustatory habituation did not appear to occur in pipeline and sanshool when used alone, at least at AFC50 concentration of the fourth instar. Cross-habituation occurred in the piperine-experienced group when tested under the condition of sanshool versus control, but not vice versa.Taken together, the feeding experiences of tomato, tobacco, and cotton could re-shape larval olfactory system, so did adult host-contacting experience, but the latter could only mask the innate ovipositional preference but could not reverse it.