Interactions between Larval Parasitoids and Their Hosts

The Interactions between 7

Larval Stage Parasitoids

and Their Hosts

Michael R. Strand

Department of Entomology, 420 Biological Sciences Building,

University of Georgia, Athens, GA 30602–2603, USA

Introduction

Parasitoids are free-living insects as adults, but are parasites of other

arthropods during their immature stages. Hosts are usually located by the

adult female, who lays her eggs in or on the host’s body. The parasitoid

larva then completes its development by feeding on host tissues. A few

parasitoids oviposit in only the general proximity of where hosts occur.

Hosts are then parasitized by either ingesting a parasitoid egg or are

located by mobile parasitoid larvae. Most parasitoids have limited host

ranges and parasitize only a specific life stage (egg, larval, pupal or adult).

Most parasitoids also complete their development by feeding on only one

host, and hosts are almost always killed as a consequence of being parasit-

ized. Parasitoids in which a single offspring develops per host are referred

to as solitary species, while those that produce two or more offspring per

host are called gregarious. Parasitoids are also distinguished by whether

larvae feed on the outside (ectoparasitoids) or inside (endoparasitoids) of

hosts, and whether hosts cease to develop after parasitism (idiobionts)

or remain mobile and continue to grow after parasitism (koinobionts).

Idiobionts include ectoparasitoids that permanently paralyse their hosts

and endoparasitoids that attack sessile host stages, such as eggs or pupae.

Most koinobionts are endoparasitoids that parasitize insect larvae. Taxo-

nomically, approximately 80% of all parasitoids belong to the order

Hymenoptera (ants, bees and wasps), 15% to the order Diptera (flies),

and the remaining species are restricted to a few genera of Coleoptera

(beetles), Neuroptera (lacewings, ant-lions) and Lepidoptera (moths and

butterflies) (Quicke, 1997). There are approximately 70,000 described

species of parasitoids, which constitute about 9% of all insects. However,

some estimates suggest that up to 20% of all insects are parasitoids and

CABInternational2002.The Behavioural Ecology of Parasites
(eds E.E. Lewis, J.F. Campbell and M.V.K. Sukhdeo) 129