Parasitoids

Parasitoids of Agromyzidae by Professor Sir Charles Godfray

Anyone who tries to rear agromyzids will quickly encounter their numerous parasitoid wasps.  Some of these are astoundingly beautiful insects, at least when examined with a good lens or binocular microscope.  These notes are aimed to be an introduction to agromyzid parasitoids, and an entry into the relevant literature.  These wasps are fascinating in themselves, and there is still much to be discovered, but are also an important scientific resource.  The food webs centred on leafminers and their parasitoids are some of the best understood of all plant-herbivore-natural enemy webs and have provided significant ecological insights.  Please don’t discard your parasitoids!

Biology

Parasitoids are insects whose larvae develop by feeding on the body of another insect.  They differ from parasites in invariably killing their hosts, and from predators in only requiring one host insect for their complete development.  Nearly all agromyzid parasitoids are solitary, only one parasitoid developing per host; in other systems several to hundreds of gregarious parasitoids develop on a single host.  Agromyzid parasitoids have two main types of biology:

Ectoparasitoids.  A female parasitoid locates a host and stings it, leaving it paralysed, and lays an egg on its body.  The egg hatches and the larva feeds externally on the host, pupating in the mine or feeding gallery.  Feeding larvae or pupae can easily be seen in back-lit leafmines (Fig. 1).  Because the agromyzid does not grow after attack, some of the parasitoids that develop on young hosts are very small, much smaller than the fly.  Typically, males develop on small hosts and females on larger hosts.