Effects Of Intra-and Inter Specific Egg Predation On Developmental Performances And Oviposition Selection Behavior Of Three Lady Beetles

Generalist predatory lady beetles are of importance in aphid pest control in their native and introduced areas as well.Harmonia axyridis and Coccinella septempunctata,for example,native to Asia,become effective biological control agents after introduced into North America and Europe against aphids and other insect pests.However,their highly competitiveness threatens native ladybird diversity,leading to a growing debate about their benefit and harm.Cannibalism and intraguild predation are common in aphidophagous predators,and attributed as causes of the ladybird invasiveness in North America and Europe.In my thesis study,I first made a feeding experiment to examine the impact of cannibalism and intraguild predation on the developmental performance of H.axyridis,C.septempunctata,and then performed a choice trial to examine the effect of predation risk on oviposition strategy.1.Effects of conspecific egg predation on developmental performances of Harmonia axyridisTo examine the impact of cannibalism on the development and survival in H.axyridis,a feeding experiment was made to observe developmental performance of H.axyridis larva,pupa and adult,which fed on either aphids(control)or conspecific eggs from neonate.The results indicated that H.axyridis developed well and survived feeding conspecific eggs and aphids.Survival of H.axyridis neonates to the next instar was over 90%when feeding on conspecific eggs,and significantly higher than feeding on aphids.However,the survival of H.axyridis emerge to adult when feeding on conspecific eggs was lower than aphids.Although neonate developmental duration to the next instar was shortened when feeding on conspecific eggs as opposed to aphids,developmental duration of 2nd larva to adult was significantly prolonged.Body weight of 2nd to 4th larva,pupa and adult when feeding on conspecific eggs were significantly lower than feeding on aphids.These results suggest that conspecific eggs can make H.axyridis complete the entire development,mainly benefiting the survival and development of neonate larvae.2.Effects of intra-guild egg predation on neonate larva development in three predatory ladybeetlesFeeding experiments were conducted to examine neonate developmental performance of three sympatric ladybird beetles,Propylea japonica,Coccinella septempunctata,and H.axyridis,which fed on aphids(control),conspecific or heterospecific eggs.The results indicated that H.axyridis eggs were lethal or sub-lethal to P.japonica and C.septempunctata neonate larvae,whereas the reverse was not the case.Survival rate from the 1st to 2nd stadium in P.japonica was almost seven-fold higher when feeding on conspecific and C.septempunctata eggs than on H.axyridis eggs.C.septempunctata neonates did not survive to the next instar when feeding on H.axyridis eggs,whereas over 85%survived when feeding on other types of food.In contrast,survival of H.axyridis neonates to the next instar was over 90%when feeding on either conspecific or heterospecific eggs.Although P.japonica and C.septempunctata neonate developmental duration to the next instar was prolonged when feeding on heterospecific as opposed to conspecific eggs,H.axyridis neonates did not exhibit the difference between feeding heterospecific and conspecific eggs.Both P.japonica and H.axyridis neonate larvae ended up with body weight gain at molting into the 2nd instar as same when feeding on conspecific eggs as when feeding on heterospecific eggs,whereas C.septempunctata neonate larvae decreased body weight gain when feeding on P.japonica eggs as compared to feeding on conspecific eggs.Our study results suggest that H.axyridis eggs are toxic to both C.septempunctata and P.japonica neonate larvae,but the reverse is not true,thereby validating the supposition that chemical defense of H.axyridis eggs may be a potential factor for population declines of native ladybirds in North America and Europe.3.Oviposition behavior of Coccinella septempunctata and Harmonia axyridis in the presence of conspecifics and heterospecificsA choice experiment was conducted to examine C.septempunctata and H.axyridis oviposition responses in relation to conspecific and heterospecific adult tracks and eggs in the laboratory.(1)C.septempunctata was deterred from ovipositing on plants in the presence of conspecific and heterospecific adult tracks and eggs,without significant differences between conspecific and heterospecific track treatments.The deterring effect of heterospecific adult tracks and eggs was stronger than that of conspecific counterparts.(2)H.axyridis was deterred from ovipositing on plants in the presence of conspecific adult tracks and eggs,but not in the presence of heterospecific adult tracks and eggs.The results of this study suggest that both C.septempunctata and H.axyridis avoid ovipositing in the presence of conspecificadult tracks and eggs,whereas C.septempunctata also avert ovipositing in the presence of heterospecific adult tracks and eggs.