A Parasitic Wasp (Eretmocerus mundus Mercet) Can Exploit Chemically Induced Delays in the Development Rates of Its Whitefly Host (Bemisia tabaci Genn.)

Sublethal plant defences, resulting in impaired growth of insect herbivores, may increase the impact of natural enemies upon those herbivores. This study examined whether such effects could be reproduced by chemically altering host growth rates. Fresh residues of piperonyl butoxide (a compound which slows growth in nymphs of the whitefly, Bemisia tabaci (Gennadius)) showed relatively little toxicity to adults and larvae of the parasitoid Eretmocerus mundus (Mercet), and once residues were 48 h old, they caused no discernible lethal or behavioral effects on adult wasps. Piperonyl butoxide had lethal effects on whitefly nymphs, but immature parasitoids continued to develop successfully in those hosts that survived. The hypothesis that slowing the growth rate of hosts might lead to increased parasitism by E. mundus was tested on large host populations in controlled temperature cabinets over two generations. On host populations of comparable size, highly significant increases in parasitism (7–8%, P < 0.0001) were observed. This work provides unique evidence that host growth rates can be artificially manipulated to confer advantage to parasitoids. The implications for biological control strategies and an understanding of plant allelochemical effects are discussed.