Biological Control of Aphids Using Parasitoids
Answer: Biological control of aphids entails correctly identifying the aphid or aphids attacking your horticultural crops so you can select the appropriate parasitoid. However, if you have multiple aphid species then you can purchase “mixtures” of two parasitoids. For example, the container in Figure 1 has two parasitoids; one for “large” aphids (Aphidius ervi) and one for “small” aphids (Aphidius colemani).
You may also want to consider using a banker plant system (Figure 2), which consists of non-crop plants that provide alternative food sources (prey) to enhance establishment of the parasitoids. Below are descriptions of four aphid parasitoids that are commercially available from most biological control suppliers/distributors:
1. Aphidius ervi
Aphidius ervi (Figure 3) parasitizes “large” aphid species, such as the potato (Macrosiphum euphorbiae) and foxglove (Aulacorthum solani) aphid. Adults are 4 to 5 mm long, black, with long antennae. The development time from egg to adult is contingent on temperature. For instance, the life cycle (egg to adult) takes 14 days at 70° F and 20 days at 59° F. Females have “high” searching capacity. Females use their antennae to examine an aphid host in order to assess size and determine if the aphid has already been parasitized. Females lay eggs into aphids by means of rapid movement of the abdomen. A female will curl her abdomen under her body and then “poke” the aphid using her ovipositor (egg-laying device) to insert an egg. Eggs hatch into larvae that consume the internal contents of aphids. The parasitized or “mummified” aphids are golden-yellow to brown in color. Aphidius ervi can parasitize many aphids in a day.
2. Aphidius colemani
Aphidius colemani (Figure 4) parasitizes “small” aphid species including: green peach (Myzus persicae) and cotton/ melon (Aphis gossypii) aphid. Adults are 2 to 3 mm in length with long antennae. Adults possess “high” searching ability in that they can locate low populations or small patches of aphid colonies on plants. The mummies associated with aphids parasitized by A. colemani are leathery and golden-brown in color. The life cycle is similar to A. ervi (described on pg. 14).
3. Aphelinus abdomalis
Aphelinus abdomalis parasitizes potato and foxglove aphids, and other aphid species. Adults are small (3.0 mm long) with short antennae, black and yellow, and are more compact in shape than either A. ervi or A. colemani. Females approach an aphid and then insert eggs, using her ovipositor, into the aphid while walking backwards. The mummies affiliated with aphids parasitized by A. abdomalis are black. The black mummy forms in approximately seven days after an egg is inserted and then after 14 days, an adult emerges from the “mummified” aphid. Aphelinus abdomalis females will host-feed on aphids killing about two aphids per day. Aphelinus abdomalis prefers to walk on a crop instead of flying.
4. Aphidius matricariae
Aphidius matricariae parasitizes green peach aphid, and is similar in appearance to A. colemani. Adult females may live between 15 to 17 days, parasitizing more than 200 aphids in addition to killing aphids when host-feeding. Females’ host-feed in order to obtain nutrition.
Raymond A. Cloyd is professor and extension specialist in horticultural entomology/plant protection at Kansas State University. He can be reached at email@example.com.