Parasitoid Wasps (Aphidus spp.)

Aphidius colemani, Aphidius ervi and Aphelinus abdominalis are all natural aphid parasites and very useful and effective for the prevention and low-infestation management of various aphid species. These 2-3 millimeter mini-wasps are best used for preventing the establishment of more than 40 species of aphids. They can also tackle light to medium infestations. And, if established, they can adequately protect a crop throughout the season.

Aphidius colemani, which are normally shipped as ready-to-emerge mummies (expect to see some hatched adults on arrival), seem to be the product of choice when melon or cotton aphids (Aphis gossypii) are present as these are typically the aphid species on which they are reared. But it will also attack the green peach aphid (Myzus persicae), the tobacco aphid (Myzus nicotianae) and the bird cherry-oat aphid (Rhopalosiphum padi) commonly used on banker plants.

Aphidus_ervi.jpeg

Aphidius ervi, is shipped as mummies (expect to see some hatched adults on arrival), and is an excellent parasite of potato aphid (Macrosiphum euphorbiae), foxglove aphid (Aulacorthum solani) and the pea aphid (Acyrthosiphon pisum). A strong flier, it can locate small aphid colonies, making it excellent for preventive applications. Capable of parasitizing hundreds of aphids, it can be used for curative applications, but should be used in conjunction with aphid predators such as green lacewings.

Aphid Parasite - aphelinus abdominalis.jpg

Aphelinus abdominalis is a specialized parasitoid of aphids. Female Aphelinus select aphids by palpating them with their antennae. Having located a host aphid of an appropriate size and species, the tip of the ovipositor is inserted into the ventral surface of the aphid and an egg is laid. The egg hatches within the aphid and the resulting larva consumes the body contents, finally feeding on vital organs when nearly fully grown. The aphid host continues to feed and grow during this process and may initially produce some offspring. As the development of the parasite larva proceeds this ceases. When the parasite larva is fully grown the host dies and a distinctive black mummy is formed. At (68°F) 20°C this occurs 7 days after parasitism. The mummy then takes a further 14 days to develop before an adult wasp emerges. In one of the principal hosts, Macrosiphum euphorbiae, Aphelinus prefers to parasitize second and third instar aphids. Larger aphids are less frequently attacked, while first and small, second instars are used as a source of food by the adults. This host feeding is an important source of mortality in the aphids, with each female A. abdominalis killing approximately 2 aphids per day. By host feeding, the parasite obtains a source of proteins, which allows it to continue development of eggs and so increase the total number of offspring it produces.

Target Pest: Aphids

Parasitic wasps are very often used to control populations of agricultural pests. Aphelinus first searches its prey with its antenna. Then it swings around and curls up the tips of the wings. The female stabs her ovipositor into the aphid, to paralyze it.

Optimal Environment: The conditions for optimum performance will be between 64-75°F with a relative humidity of around 80%. But these are optimum conditions and not necessarily a prerequisite of successful implementation. Please note, however, significantly cooler or warmer temperatures and humidity fluctuations may hamper reproduction and development a certain degree.

Release Rates:

Aphidius colemani

Preventative: 1-5 per 100 square ft., weekly

Hot spots: 5-25 per 100 square ft., weekly

Aphidius ervi

Preventative: 1-5 per 100 square ft., weekly

Hot spots: 5-25 per 100 square ft., weekly

Aphelinus abdominalis

Preventative: 2-5 per 100 square ft., weekly

Hot spots: 10-25 per 100 square ft., weekly

Lifecycle: These parasitoids work by laying eggs in aphids. And they can lay 200-300 eggs! The wasps’ larvae which hatch from the eggs, slowly weaken and kill the aphids from within (endoparasitism). The aphids then turn into “mummies” as the wasps pupate. The life-span of these parasitoids is roughly 2 weeks in their immature stages, then 2 weeks as adults.

Strategic Considerations: Yellow sticky traps should be removed prior to releasing these mini-wasps. To monitor for thrips, use blue traps. If yellow traps must be used for whiteflies, etc., hang them for only two days per week. Ants, if present, should be controlled. They will defend aphids from predators and parasites to protect their honeydew food. Use barrier, exclusion products or boric acid products to control the ants. If your planting doesn’t have any ants, check to be sure that the honeydew isn’t too heavy. This may prove to be a hindrance to the parasitoids’ performance; they may spend too much time cleaning themselves.

Selected References

University of Maryland. College of Agriculture and Natural Resources. Parasitoid Wasps (Hymenoptera).

UC IPM. Aphidius spp.

Aphelinus abdominalis – Sound Horticulture

Aphid Control with Aphidius & Aphelinus parasites - GreenMethods