Attracting parasitoids by plants as defences against herbivorous insects

菜粉蝶幼虫专化性寄生小蜂Cotesia regregata(L.)的雌蜂被菜粉蝶(P.rapae L.)、甜粉蝶(P.Melete Menetries)和甘蓝型油菜粉蝶(P.napi L.)幼虫危害的十字花科植物Rorippa inca(L)叶片中的挥发性化学物质引诱。他们的影响持续了五天多。机械危害或其他食草性昆虫的危害对寄生蜂的影响较小。因此，这种植物可能会产生挥发性化学物质来帮助寄生蜂攻击幼虫。然而，这种植物通过吸引寄生蜂所获得的好处并不是马上就能显现出来。当幼虫被寄生蜂杀死时，它们的取食活动就完全结束了。因此，植物通过生产诱人的化学物质来帮助拟鹦鹉攻击幼虫并不是直接有益的。因此，如果蝴蝶通过附近植物上的卵在这些植物上生长，负责帮助寄生蜂寄生的植物的基因将受到自然选择的青睐。这三个种都有有效的规避/防御机制。这种机制很可能是植物和寄生蜂合作的结果。我们试图解释，被蝴蝶幼虫危害的植物印度小蜂已经进化产生了一些挥发性化学物质，吸引了寄生小蜂。

Females of Cotesia glomerata (L.) (=Apanteles glomeratus L.)., a specialist parasitoid wasp of Pieris butterfly larvae, are attracted to volatile chemicals from leaves of a cruciferous plant Rorippa indica (L) Hieron damaged by larvae of three Pieris species, P.rapae L., P.melete Menetries and P.napi L. The volatile chemicals are emitted neither from saliva of Pieris larvae nor from leaf juice of the plant. Their effect continued for more than five days. Mechanical damage or damage by other herbivorous insects had less effect on the parasitoid. Therefore, this plant likely produces volatile chemicals to help the parasitoid attack the Pieris larvae.However, what the plant gains by attracting the parasitoids is not immediately obvious. When the Pieris larvae are killed by the parasitoid, their feeding activities have completely finished. Thus, it is not directly beneficial for the plant to help the parsitoid attack the larvae by paying the cost of producing attractive chemicals.Nearby conspecific plants of R.indica seems to be kin plants each other. Therefore, if butterflies grown on those plants by eggs on the nearby plants, genes of the plants responsible for helping the parasitoid parasitized will be favoured by natural selection. Each of the three Pieris species has effective avoidance/defense mechanisms against C.glomerata. Such mechanisms may well be the result of co-operation between plant and parasitoid. We attempted to interpret that plant R.indica damaged by larvae of Pieris butterfly species has evolved to produce some volatile chemicals attracting the parasitoid C.cotesia.