Genus. Pediculoides.
Pediculoides ventricosus, Newport, 1850.
Syn.: Heteropus ventricosus, Newport, 1850; Acarus tritici, Lagrèze-Fossot, 1851; Physogaster larvarum, Lichtenstein, 1868; Sphærogyna ventricosa, Laboulbène and Mégnin, 1885.
Males are oval in shape, 0·12 mm. in length and 0·08 mm. in breadth, flattened. There are six pairs of chitinous hairs on the dorsal surface and a lyre-shaped lamella on the posterior part. The female in the non-gravid state is cylindrical in form, 0·2 mm. in length and 0·07 mm. in breadth; when gravid the posterior part of the body becomes enlarged into a ball, which may attain 1·5 mm. in size, as in the case of Pulex penetrans and of the female Termites. On emerging the young are already provided with four pairs of legs and copulate soon after birth.
Fig. 353.—Pediculoides ventricosus. a, male; b, young female; c, gravid female. Enlarged. (After Laboulbène and Mégnin.)
These animals live on the stalks of cereals, and feed on vegetable and animal juices; they are also found on corn-infesting insects. They invade the barns and seek out the insects living in the dry grains of corn, or wait for an opportunity of obtaining food. They have been repeatedly observed on human beings, particularly labourers occupied in handling grain; their bite causes severe irritation, local elevation and reddening of the epidermis, as well as fever. It cannot be positively asserted that all cases of the occurrence of cereal mites on man relate to P. ventricosus, as the descriptions are often insufficient. Geber states that one form is Chrithoptes monunguiculosus, or Acarus hordei; Flemming mentions Tarsonemus uncinatus; Koller Oribates sp.; and Karpelles Tarsonemus intectus.
[The pregnant female Pediculoides has a large round inflated abdomen, in which the ova hatch and the young mature. Later they escape from the parent as adults.—F. V. T.]