Lepidopteran larval parasitoids
Locally occuring parasitoids can be highly effective at suppressing pest populations, and there is a wide diversity of parasitoids that target the caterpillars of lepidoptera (moths and butterflies). In Australia, the families Braconidae and Ichneumonidae are the most prevalent parasitoids associated with caterpillar biological control.
Braconidae and Ichneumonidae exhibit similarities in appearance and ecological behavior. Ranging in size from 10mm to 250mm, with Ichneumonidae generally being larger, they display bright markings and females possess a long ovipositor.
Female wasps lay their eggs on or inside caterpillar bodies, often depositing hundreds of eggs throughout their lifespan. The number of eggs per host varies among parasitoid species, ranging from multiple eggs to a single egg.
Parasitoid development relies on the caterpillar host, with the parasitoid larvae feeding on the caterpillar until pupation. The adult parasitoid emerges, while the caterpillar succumbs to the parasitoid's presence. Developmental times vary by species and temperature, typically taking about one to two weeks.
Identifying lepidoptera larval parasitoids requires careful observation. Look for signs of abnormal behavior or physical abnormalities in caterpillars. Parasitized caterpillars may exhibit slowed movement, unusual coloration, or abnormal body shapes. Some parasitoid species develop externally, leaving small grubs or cocoons attached to the caterpillar, while others complete their development entirely inside the caterpillar, becoming apparent in later stages as the larvae develop and pupate (refer to image below).
Infected caterpillars may display altered behavior such as reduced feeding or remaining in exposed positions instead of seeking shelter. Other parasitoids permanently paralyze their hosts to prevent development.
While some parasitoid species have a narrower host range, targeting specific lepidoptera families or even individual species, others possess broader abilities to parasitize various lepidoptera hosts within a given habitat. Importantly, lepidoptera parasitoids exclusively attack and eliminate lepidoptera and do not cause harm to plants, other insects, livestock, or humans.
Parasitoids can be found in various habitats where lepidoptera are present, including greenhouse and open field crops. Adults are commonly observed at flowers or actively searching for hosts around trees, vegetation, or plant litter. 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.