by Mark Hoddle, Department of Entomology, University of California, Riverside
Eretmocerus eremicus is a tiny parasitic wasp (~1 mm in length) that is indigenous to the southern desert areas of California and Arizona (Rose and Zolnerowich, 1997) and is an important parasitoid of whiteflies in these areas (Hunter et al., 1996).
Female E. eremicus are pale lemon yellow with green eyes and clubbed antennae. The name Eretmocerus is derived from Latin, meaning "oar-like," and refers to the shape of the female antennae. Male wasps have longer, elbowed antennae, and are yellowish brown in color. Whitefly pupae that have been parasitized by E. eremicus appear beige in color whereas healthy whitefly pupae are white or pale yellow. This aphelinid parasitoid does not deposit fecal-like material within the host before emergence as do some other parasitoids of whiteflies. E. eremicus can only emerge through the upper surface of the host. This is accomplished by chewing a circular exit hole.
E. eremicus have been released inundatively in the Imperial Valley of California, to control Bemisia argentifolii on cotton. Inundative releases have also been made to suppress whiteflies infesting ornamental and vegetable crops in greenhouses.
E. eremicus attacks whiteflies (Homoptera: Aleyrodidae) including greenhouse whitefly (Trialeurodes vaporarium), sweetpotato whitefly (B. tabaci), silverleaf whitefly (Bemisia argentifolii), and bandedwinged whitefly (T. abutlonea).
Both male and female E. eremicus develop as primary parasitoids of whiteflies. In commercial mass rearing with greenhouse whitefly as the host, this wasp has a sex ratio of 1:1 (female:male), however in the field the sex ratio may favor females. E. eremicus females locate whitefly hosts, in part, by olfaction. Females lay their eggs between the whitefly nymph and the leaf surface. Females will oviposit under all immature whitefly stages, except eggs, but second instars may be preferred.
The E. eremicus egg hatches about 4 days after being laid (the exact time is dependent on temperature) and the wasp larva develops as an external-internal parasitoid. The newly emerged larva attaches its hook-like mouthparts to the underside of the whitefly nymph and chews a small hole into the whitefly. After 3-4 days of chewing the parasitoid larva enters the host where it remains dormant until the whitefly pupates. Once the whitefly pupal stage is reached, the wasp larva releases digestive enzymes, and begins ingesting the semi-liquid body parts of the pupa.
The wasp larva passes through three instars, requiring about 12 days to complete development. The adult wasp chews its way out of the whitefly cadaver. Adult female wasps can live for 6-12 days at 27°C. Longevity depends on temperature and availability of food, such as honeydew produced by whiteflies. Females lay 3-5 eggs per day. Female wasps also kill whitefly nymphs by repeatedly probing with their ovipositors and feeding on the haemolymph (blood) that exudes from the wound.
E. eremicus is an aggressive searcher, covering around 1.3 mm/s on some plants. Females will inspect all whitefly stages with the same relative frequency as their encounter rate. Around 74% of nymphs that are probed with the ovipositor are parasitized. Optimum temperatures which will facilitate rapid development and egg production occur at 25-29°C. In the greenhouse environment, the temperature should be manipulated to ensure that E. eremicus will develop more quickly than its host. On greenhouse grown poinsettia in the northeastern US, a release rate of 3 female E. eremicus/plant/week achieves very high levels of mortality (> 98%) of silverleaf whitefly in the first 6-8 weeks of the crop.
E. eremicus is assumed to be susceptible to pesticide residues and fumigants. Releases of E. eremicus will be most effective in crops that have not been sprayed for 10-14 days. Employ the Encarsia formosa recommendations for E. eremicus from the Koppert side effect list of pesticides for beneficial organisms (available from Koppert Biological Systems).
Gerling, D., (1965) Studies with whitefly parasites of Southern California II. Eretmocerus californicus Howard (Hymenoptera: Aphelinidae). The Canadian Entomol. 98: 1316-1329.
Headrick, D. H., Bellows, T. S., Perring, T. M., (1995) Behaviors of Eretmocerus sp. nr. californicus (Hymenoptera: Aphelinidae) attacking Bemisia argentifolii (Homoptera: Aleyrodidae) on sweet potato. Environ. Entomol. 24: 412-422.
Hunter, M.S., Antolin, M.F. & Rose, M. (1996) Courtship, behavior, reproductive relationships and allozyme patterns of three north American populations of Eretmocerus nr. californicus parasitizing the whitefly Bemisia sp. tabaci complex (Homoptera: Aleyrodidae). Proceedings of the Entomological Society of Washington 98: 126-137.
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Rose, M. & Zolnerowich G. (1997) Eretmocerus Haldeman (Hymenoptera: Aphelinidae) in the United States with descriptions of new species attacking Bemisia (tabaci complex) (Homoptera: Aleyrodidae). Proceedings of the Entomological Society of Washington 99: 1-27.