三种瓢虫集团内捕食卵对初龄幼虫生长发育的影响

种内和种间捕食卵现象常见于对食蚜瓢虫的研究报道中。源自亚洲、入侵北美和欧洲的异色瓢虫(Harmonia axyridis)由于卵含有生物碱而被认为可能是威胁本土瓢虫生存的原因,但该推测只有在明确异色瓢虫在原产地是否对本土瓢虫具有类似负面影响后,才能确证。通过饲喂实验,旨在明确异色瓢虫在原产地是否对本土七星瓢虫(Coccinella septempunctata)和龟纹瓢虫(Propylea japonica)具有食卵负面作用,为揭示异色瓢虫入侵机理提供依据。实验中用蚜虫(对照)和3种瓢虫卵对瓢虫初孵1龄幼虫进行饲喂处理,观察幼虫生长发育指标。对瓢虫初龄幼虫存活表现的分析结果表明:(1)龟纹瓢虫初孵幼虫取食同种卵和七星瓢虫卵后存活至2龄的比率均高于取食异色瓢虫卵的近7倍;(2)七星瓢虫幼虫取食异色瓢虫卵未存活到2龄,但取食其他瓢虫卵和蚜虫后85%以上个体存活至2龄;(3)异色瓢虫初孵幼虫取食同种和其他2种瓢虫卵后有90%以上存活至2龄。龟纹瓢虫和七星瓢虫1龄幼虫取食异种卵比同种卵后的发育历期显著延长,但异色瓢虫并未表现出差异。龟纹瓢虫和异色瓢虫1龄幼虫取食同种和异种卵后的体增重相同,但七星瓢虫取食龟纹瓢虫卵后体增重比取食同种卵减小。研究结果说明,异色瓢虫卵对七星瓢虫和龟纹瓢虫初孵幼虫的生存具有负面影响,反之不然。所以,取食异色瓢虫卵本身并非是导致北美和欧洲本土瓢虫数量减少的原因。

Effects of intra-guild egg predation on neonate larva development in three ladybird beetles (Coleoptera: Coccinellidae)

Intra- and inter-specific predation of eggs is well documented in aphidophagous ladybird beetles. Chemical defenses of eggs of Asia-originated invasive Harmonia axyridis is the possible reason for population declines of native ladybirds in North America and Europe. However, this supposition cannot be confirmed without determining whether H. axyridis eggs are toxic to native ladybirds in its original areas. To investigate mechanisms responsible for H. axyridis invasion, we conducted a feeding experiment 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 from the 1^st to the 2^nd instar stage 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 2^nd 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 not confirming the supposition that chemical defense of H. axyridis eggs is a potential factor for population declines of native ladybirds in North America and Europe.