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Hemisarcoptidae

Hemisarcoptidae

Taxonomic placing: Acari, Acariformes, Astigmata.

Common name: None.

Geographical distribution: Widely distributed around the world, wherever armored scale insects (Diaspididae) occur.

Morphology: These are small, whitish mites with a prodorsal sclerite. The genital and anal orifices are beyond coxae IV, confluent in the females, separate in the males. All tarsi terminate with an elongate, sucker-like ambulacrum. The hypopodes are dark brown, with a pair of eyes and a caudal, ventral attachment plate. Their tarsi lack the sucker-like ambulacra of the other stages, and the fourth pair of legs terminates with 2-3 long setae.

Biology: Hemisarcoptidae occur on insects, in nests of vertebrates or in sheltered habitats, e.g. subcortical tree bark; the life history of most forms is unknown. Hemisarcoptes is the only genus whose biology has been studied; all its species feed on Diaspididae and the hypopodes are phoretic on Adults of the genus Chilocorus (Coccinellidae), which feed on the same prey. During feeding (either as a predator of the eggs or as an ectoparasitoid of the other stages) the bodies of the whitish mites acquire the colour of the body fluids of the host scale. Hemisarcoptes spp. prefer to attack ovipositing host females, and usually mate thereon, prior to dispersal. Under optimal conditions (around 25°C) a generation may be completed in a fortnight and each female produces 40-60 eggs. In the field the sex ratio may fluctuate widely (often depending on the host), but tends to be 1:1. These mites are very tolerant to harsh conditions, being able to survive and reproduce in very cold or hot climates.

When the development of the mite’s larvae or protonymphs is undisturbed and rapid, the latter stage molts to become the tritonymph. But if development is prolonged for any reason, especially lack of food, the protonymph molts to the deutonymph, the hypopus, which is attracted to and dispersed by Chilocorus spp. This phoresy enables the mites to find new hosts/prey in unexploited areas, facilitates their dispersal between patches over short or long distances, and the dark integument protects them against desiccation and radiation during dispersal. The termination of the hypopodial period, after a minimal sojourn on the beetles, seems to be triggered by environmental and chemical cues, such as humidity and the presence of hosts. The location and number of hypopodes on the beetles seems to be determined by the pattern of microsetae, or spines, that are located on the elytra’s underside. Areas of dense spines (located mostly along the anterior margin of the wings) are unsuitable for the mites, which prefer the smoother surfaces. The specificity of Hemisarcoptes for Chilocorus is probably genus- rather than species- specific, and in rare cases, when these beetles are not available, the mite may also attach itself by other Coccinellidae.

Economic importance: These mites are efficient natural enemies of several armored scale insect pests (e.g. Parlatoria blanchardi in the Sahel or Lepidosaphes ulmi in Canada). Their efficacy seems to depend on the particular host attacked and on the absence of other, more efficient natural enemies. Except for Hemisarcoptes spp., other members of this family do not have any economic importance.

References

Calmasur, Ö. and Özbek,H. 2007. Biological observations on Hemisarcoptes coccophagus Meyer (Acari: Astigmata: hemisarcoptidae) associated with willow armored scale, Chionaspis salicis (L.) (Hemiptera: Diaspididae) in Erzurum, Turkey. Proceedings of the Entomological Society of Washington 109: 829-835._

Gerson, U., OConnor, B.A. and Houck, M.A. 1990. Acari. In: Rosen, D. (ed) Armored Scale Insects: Their Biology, Natural Enemies and Control, Volume 4B, pp. 77-97. Elsevier, Amsterdam.

Houck, M.A. 1999. Phoresy by Hemisarcoptes (Acari: Hemisarcoptidae) on Chilocorus (Coleoptera: Coccinellidae): influence of subelytral ultrastructure. Experimental and Applied Acarology 23: 97-118.

Houck, M.A. and OConnor, B.M. 1996. Temperature and host effects on key morphological characters of Hemisarcoptes cooremani and Hemisarcoptes malus (Acari: Hemisarcoptidae). Experimental and Applied Acarology 20: 667-682.

Izraylevich, S. and Gerson, U. 1995. The hypopus of Hemisarcoptes coccophagus Meyer: distribution and apolysis. Acarologia, 36: 333-339.

Ji, L., Gerson, U. and Izraylevich, S. 1994. The mite Hemisarcoptes sp. (Astigmata: Hemisarcoptidae) parasitizing willow oyster scale (Homoptera: Disapididae) on poplars in Northern China. Experimental & Applied Acarology 18: 623-627.

Lord, F. T. and MacPhee, A.W. 1953. The influence of spray programs on the fauna of apple orchards in Nova Scotia. VI. Low temperatures and the natural control of the oystershell scale, Lepidosaphes ulmi (L.) (Homoptera: Coccidae). Canadian Entomologist 85: 282-291.

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