Non-consumptive Effects Of Predator On Developmental, Behavioural And Physiological Performance Of Helicoverpa Armigera

The relationship between predator and prey is a basic food web interaction that cascades to influence ecosystem properties and functions through both direct and indirect effects. Although researches have been mainly focused on the direct consumptive effect (CE), both theoretical and experimental work suggests that the non-consumptive effect (NCE) can equal or exceed the effect of direct consumption. NCE is ubiquitous in almost all kinds of species in nature, inducing significant and profound changes in phenotypic plasticities, genetics and population dynamics of prey animals. Arousing attentions have been paid to NCE in a wide range of animal taxa, however, insects, especially terrestrial species, including cotton ballworm (Helicoverpa armigera), are under-represented in studies of NCE. Therefore, the relative researches will provide new clues to clarify the mechanism underlying the induced responses of H. armigera and possibly other holometabolous insect herbivores to non-consumptive predation risk. In this paper, Helicoverpa armigera Hubner (Lepidoptera:Noctuidae), an omnivorous, cosmopolitan pest in terrestrial ecosystem, was used as the prey animal, and its responses to different types of non-consumptive predator stress on ontogeny, reproduction, behavior and physiology were observed. Our main conclusions are as follows:H. armigera was capable of recognizing the risk from the two nonlethal predatory natural enemies used in the tests, namely ladybugs Harmonia axyridis and mercerizing starlings Sturnus sericeus, and showed significant responses in many aspects:(1) After being exposured to non-consumptive predator stress from H. axyridis over three successive generations, H. armigera induced faster development, advanced metamorphosis, inhibited metamorphic success and increasing reproductive effort when food was abundant; (2) Through chronic (long-term) exposure for whole life stages as well as acute (short-term) exposure for 6h on 3rd-instar larvae from non-consumptive H. axyridis, the relative expression of stress-related protein genes hsp70, hsp90, and hsc70 of H. armigera from both treatments showed rise trend at different degree; (3) The outdoor experiments indicated that H. armigera larvae from stress group preferred the lower part, leaf center and stalk of the plant, and 3rd-instar larvae presented more dynamic behaviors than static behaviors when threatened by S. sericeus, meanwhile, the indoor tests suggested that predator stress increased food intake of H. armigera larvae when supplies were abundant, while no significant effect on total population decline caused by cannibalism occurred; (4) Through testing enzymatic activity of peroxidase(POD), catalase(CAT)and superoxide dismutase (SOD) of 3rd instar H. armigera larvae exposed to non-consumptive S. sericeus, increases in POD and SOD enzymatic activity were found at a few time points within 24 hours.Non-consumptive effects of predatory natural enemy on H. armigera couled be influenced by many factors, such as food source signals of predator, developmental stage of prey, stress time duration and so on:(1)H. armigera. responded with larger decrease on pupal weight to stimuli from H. axyridis fed a diet of eggs or larvae of H. armigera than any other food source group, indicating that reaction of H. armigera to predation risk signals from homologous threatened prey might be more intense; (2) Expression of hsp70 and hsp90 changed more obviously by instantaneous stimulation while hsc70 changed more obviously by chronic stimulation from S. sericeus threaten; (3) The sensitivity of anti-predator responses of H. armigera varied in different developmental stages, for example larvae were more significantly affected, while adults hardly get effected on developmental timing, in addition, metamorphic success rate and production dynamic also differed as the NCE accumulated through generation.Our data revealed that H. armigera could implement complex strategies of phenotypic changes in response to predator stress. The defensive siginificance for H. armigera to avoid predation risk and the adaptive siginificance for the population evolution of these strateges were suggested and the potentail ecological consequences were discussed. Through the study of this paper, we hope to emphasize the indirect effects of predator on prey, to further understand both the individual-and population-level consequences of NCE, and to enrich the knowledge of complex internal relations within ecological system. Additional work is warranted to determine the broader implications of these findings for biological control as well as biological conservation outcomes.