Study On Effects Of An Artificial Diet With Non-insect Ingredient On Biological, Biochemical And Predatory Characteristics Of Harmonia Axyridis (Pallas)

The multicolored ladybeetle Harmonia axyridis (Pallas), an excellent predatory insect, is of highvalue in biological control application. At present most of artificial diets for H. axyridis result in lowfecundity and the evaluation of artificial diets are limited in biological category. In this study wedetermined the effects of an artificial diet with non-insect ingredient on the biological, biochemical andpredatory characteristics of H. axyridis, to provide theoretical basis for improvement of the artificial dietand large-scale artificial propagation. The main results obtained from this research were as follows:1. The effects of the artificial diet and the natural prey Acyrthosiphon pisum (Harris) on thebiological characteristics of H. axyridis were determined. The results showed that H. axyridis couldcomplete the whole life cycle on the artificial diet individually and lay a small number of eggs. Younglarvae survived better on the artificial diet while elder larvae did better on A. pisum, which indicatedthat larvae fed on the artificial diet/prey during young/elder instars would have the highest survival rate.The artificial diet had significant influences on the growth and development of H. axyridis. Comparedwith the prey, the larvae fed on diet showed significantly longer developmental time, lower pupalweight. The artificial diet led to higher female proportion and longer life-span for adults, but had noeffects on emergence rate. There were significant effects of diets on the fecundity of H. axyridis.Compared with A. pisum, the rate of fertile female reduced, the pre-oviposition period extended, and thetotal number of eggs laid within10days declined dramatically. However, no significant difference wasfound for hatchability of eggs. The number of eggs laid by females fed on A. pisum that were treatedwith diet during larval stage accounted for80%of that by control, which indicated that the artificial dietcould be used as larval food in mass production or as extra-nutrition in storage. Using the A. pisum asstandard reference, the amino acid score (AAS) was used to find out the three limiting amino acids inthe artificial diet, which were Phe+Tyr, Lys and Arg. The supplement of the three limiting amino acidsin artificial diet produced little effects on growth or fecundity of H. axyridis.2. The impacts of the artificial diet and the natural prey on the biochemical characteristics of H.axyridis were determined. The concentration of total protein in H. axyridis fed on artificial diet is lowerthan that fed on A. pisum though without statistical significance. Feeding diet resulted in certaindecrease of enzymatic activity, among which the activities of general protease, trypsin-like enzyme andchymotrypsin-like enzyme were significantly lower compared with the control. The activities ofenzymes were different among4thinstar larvae, female and male when fed on the same food.3. The effects of the artificial diet and the natural prey on the predatory behavior of H. axyridiswere studied. The results showed that the predations of larvae, female and male adults fed on both foodswere in line with the Holling Ⅱ model. The artificial diet had effects on the functional responseequation parameters of4thinstar larvae and female, but not on male adult. The searching efficiencydeclined corresponding to the increase of prey density. The best searching densities for4thlarvae,female and male adults were forecasted by new Holling functional response model which were1:28, 1:30,1:22for H. axyridis fed on diet, and1:37,1:37,1:19for those fed on A. pisum. Therefore the H.axyridis fed on the artificial diet could perform better in pest control in the case of low prey density andwere more likely to survive when lacking prey.