Know Your Friends

Leptomastix dactylopii

Leptomastix dactylopii is a tiny parasitic wasp in the Family Encyrtidae that attacks the citrus mealybug (Planococcus citri). It does not reproduce well in other mealybug species. This wasp is a native of Brazil. It was introduced into the United States (California) and permanently established in 1934-35. L. dactylopii is used in augmentative biological control mostly in greenhouses, interiorscapes, and conservatories. It has also been used successfully in outdoor situations such as fruit plantations.

L. dactylopii is a yellowish-brown, approximately 3.0 mm long, parasitic wasp that moves around by short hopping flights. Females are generally larger than males and have non-hairy, long, straight antennae. Males have hairy, slightly bent antennae. Females live 27 days on average, whereas males live approximately 24 days. The lifecycle consists of an egg stage, 4 larval instars, pupa, and adult. The lifecycle can be completed in 18 to 25 days depending on temperature (18 days at 81F and 25 days at 75F). Adult females can live up to 35 days.

Adult female L. dactylopii are attracted to the odor of infested host-plants and of unparasitized mealybugs. They can "smell" which mealybugs have already been parasitized and avoid laying eggs in them. They prefer to lay eggs in third instar nymphs and young adult stages of citrus mealybug. They will occasionally attack second instars, but not egg-laying adults. Females can lay 60 to 100 eggs within a 10 to 14 day period. This species is a solitary endoparasitoid, meaning only a single wasp larva develops inside each mealybug. The eggs hatch in 1 1/2-2 days and the wasp larvae develop through four instars, each of which lasts about 2 days. The developing larva eventually turns the mealybug into a legless, brown, barrel-shaped mummy. After a 7-8 day pupal period, the emerging adult chews through the mummy and cuts an opening at one end. After emerging, the adult wasp feeds on honeydew produced by mealybugs, which may act as a supplementary carbohydrate source. However, it does not feed directly on the blood of its host as do many other wasps. The sex ratio is generally 1:1 with male eggs laid into small mealybugs and female eggs laid into larger mealybugs.

L. dactylopii has excellent searching abilities and can locate low densities of mealybugs. This ability makes it a good biological control agent to release when mealybug populations are low or spotty. Releases of L. dactylopii should be made near mealybug infestations at a rate of 2 per square meter of infested area or 5 per infested plant. Larger conservatory plants will require a higher release rate. Additional releases may be needed, but only one or two releases are generally necessary.

L. dactylopii is readily available from most biological control suppliers. They are normally shipped as live adults in small vials and must be released immediately upon arrival. In conservatories and/or interiorscapes they can be used in conjunction with the mealybug destroyer, Cryptolaemus montrouzieri, which feeds on the eggs or first instar mealybugs (and also feeds on many mealybug species, not just citrus mealybug which the wasp is limited to). The beetle is most useful where mealybugs occur in large colonies; the wasp is more effective when mealybugs are scattered among the plants. This combination improves the efficacy of biological control of citrus mealybug.

- Raymond A. Cloyd, Purdue University

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