Aphid parasitoids are small wasps, typically measuring 2-5 mm in length, with a slender body and distinctive narrow waist. They are commonly black or brown in color. In Australia, various families of parasitoid wasps contain numerous species that target aphids. The most prevalent genera are Aphidius, Aphelinus, Diaeretiella, Lysiphlebus, and Trioxys (subfamily Aphidiinae).
Mature female wasps lay their eggs inside aphid bodies, often depositing hundreds of eggs during their lifespan. The parasitoid's immature stages develop entirely within the aphid, feeding on it from the inside until pupation and emergence. This process results in the aphid's skin hardening, swelling, and drying into a bronze-colored "mummy." The presence of aphid "mummies" in crops indicates ongoing parasitism, suggesting that many more aphids have likely been parasitized as well.
Developmental times vary depending on the species and temperature, typically taking about one to two weeks for the immature parasitoids to emerge as adults.
While some parasitoid species have a narrower host range, targeting specific aphid families or even individual species, others possess broader abilities to parasitize various aphid hosts within a given habitat. Importantly, aphid parasitoids exclusively attack and eliminate aphid and do not cause harm to plants, other insects, livestock, or humans.
Most parasitoids can be found in any habitat where aphids are, including both greenhouse and open field crops. They thrive in protected environments with well-developed foliage, such as crops.
Creating diverse habitats with hedgerows, cover crops, brushpiles and wildflower strips can support generalist predator population, by providing additional food sources, nesting sites, and protection from pesticide exposure or extreme weather conditions. This aids parasitoid survival during non-crop periods or when crop conditions are suboptimal, improving early season control.
Many parasitoid species are highly sensitive to these insecticides, and excessive use can be detrimental to parasitoid populations and their effectiveness as biological control agents.
Consider adopting integrated pest management (IPM) practices, which involve using pesticides judiciously and as a last resort. Targeted application of pesticides, avoiding broad-spectrum ones, and selecting insecticides that have minimal impact on non-target organisms can help preserve parasitoid populations.