Intra-and Interspecific Interactions Of Myzus Persicae(Sulzer) And Lipaphis Erysimi(Kaltenbach) On Cabbage(Brassica Oleraceavar.capitata)

The green peach aphid Myzus persicae(Sulzer)and the turnip aphid Lipaphis erysimi(Kaltenbach)(Homoptera:Aphididae)are pests of cabbage and other cruciferae vegetables in most countries. Field studies of their population biology showed that the two aphid species usually co-occurred on the same plant under feasible conditions. This paper studied the intra- and interspecific interactions of M. persicae and L. erysimi on cabbage(Brassica oleraceavar.capitata). And previous infested cabbages mediated intra- and interspecific interactions between this two aphid species. We also examined the performance of either aphid species on the same cabbage leaf by previous feeding of M. persicae or L. erysimi and measured nutritional changes in the leaves ,i.e. amino acid composition and concentration. The main results are as follows:1.The density-dependent effects of M. persicae and L. erysimi were weak at the density of 5 and 10 aphids per plant. Longevity and progeny of this two species of aphids at the density of 15 aphids per plant were significantly lower than that of 5 and 10 aphids per plant. And negative density-dependent effects were observed in this two species of aphids when they reached a certain density. 2.When M. persicae and L. erysimi were reared together, their fecundities and longevity were significantly lower than that of reared alone at the density of 10 and 15 aphids per plant, indicating that the population of this two species of aphids was affected by interspecific competition. Longevity and progeny of L. erysimi were significantly lower than that of M. persicae when they were reared together at the density of 10 or 15 aphids per plant in each species, indicating that the interspecific competition of L. erysimi was less than that of M. persicae. 3.Behavioral responses of this two aphid species to healthy cabbages and infested by conspecific and hererospecific aphids were studied by using H-shaped olfactometer. The results showed that both M. persicae and L. erysimi oriented significantly towards healthy cabbages. The cabbages infested by one aphid species at the density of 50 aphids per plant had no significant effects on conspecific aphids.But at the density of 100 aphids per plant, L. erysimi preferred healthy cabbages.Both M. persicae and L. erysimi preferred healthy cabbages compared to those plants damaged by heterospecific aphids. At the density of 50 aphids per plant, M. persicae had no preference between cabbages damaged by conspecific and heterospecific aphids. But M. persicae preferred the cabbages damaged by conspecific aphids at the density of 100 aphids per plant. At the density of 50 or 100 aphids per plant, L. erysimi preferred the cabbages damaged by conspecific aphids to those damaged by heterospecific aphids.4.The reproductive rate of M. persicae was reduced by previous infestation of L. erysimi, although no effects on increase of the aphid biomass. Previous infestation by M. persicae had a strong negative effect on the reproductive rate and the increase of biomass of L. erysimi. This phenomenon indicated that the aphid infestation had a strong negative effect on the L.erysimi performance, interaction existing in this two aphid species was interspecific competition, and the effects of competition on L.erysimi were larger than that of M. persicae. 5.The performance of M. persicae and L.erysimi on leaves different from previous infested leaves had no significant difference with the control, except that the reproductive rate of L.erysimi was lower. 6.The amounts of free amino acids in the leaves infested by M. persicae was a little higher while that of in the leaves infested by L. erysimi was a little lower than that in the control leaves. On the whole, the total amount of amino acids in the leaves infested with M. persicae and L. erysimi were similar to that of in uninfested leaves. Amino acid composition in leaves infested by M. persicae and L. erysimi had little difference compared with that of in uninfested leaves, indicating that this two aphid speci...