Parasitoid wasp activity: Cotesia and Apanteles spp.

Have you seen clusters of fuzzy cocoons in your crop canopy?

You may have mistaken them for the eggs of a pest, or perhaps recognised them for what they are – the pupae of beneficial parasitoid wasps.

Parasitoid wasps are an exceptionally diverse group of insects, varying in their host, mode of parasitism, where they develop and how they emerge.

With some parastioids, egg hatching, larvae development and pupation occurs entirely within their host e.g. Trichogramma spp., Copidosoma floridanum

However, other parasitoids exit their host as larvae and pupate externally – making some species easier to spot in crops!

The lifecycle of some Cotesia and Apanteles wasps

We have recently received queries about fuzzy pupae clusters found in the field. These could very well be a species of parasitoid wasp belonging to the Cotesia or Apanteles genera.

Several species of Cotesia or Apanteles wasps begin their lifecycle after male and female adults mate, and the female wasp goes on to lay multiple eggs within a caterpillar with its ‘ovipositor’. These eggs hatch within the caterpillar and the wasp larvae feed on its host from the inside.

Despite this seeming intrusive activity, the caterpillar is still alive although they can behave a bit more sluggish than usual and can look a bit sick.

The wasp larvae grow within the caterpillar until close to pupation when they chew small holes in their host and erupt en masse into the outside world.

Parasitoid wasp larvae erupting from a cabbage white butterfly larva. Photo by Kathy Overton

Soon after emerging from the caterpillar, they spin a white silken cocoon and pupate on or close to the dying/dead body of their host.

Eventually an adult wasp will emerge from each pupa.

This form of parasitism can occur in several species of moth and butterfly larvae. Two pest species which are often seen parasitised like this are the cabbage white butterfly and armyworm.

Use these furry cocoon clusters as an additional indicator that natural enemies are at work in your paddock.

Cover image: Photo by Kathy Overton

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PestFacts south-eastern keeps growers and advisers informed about invertebrate pests and beneficials in broadacre crops and pastures during the winter-cropping season in Victoria and southern New South Wales.


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Since 2019 PestFacts south-eastern has been running through IPMforGrains: Best Practice Insect Pest Management, a project delivered by the National Pest Information Network (Cesar Australia, DPIRD, QDAF, NSW DPI, and SARDI). This project aims to provide grain growers and advisors with information on invertebrate grain pest occurrence and equip industry with the knowledge needed to implement integrated pest management practices. This initiative is a GRDC investment and includes in-kind contributions from all project partner organisations.

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