166 Acarology 



"sphere" in order to obtain food. They do not leave the mother but 

 remain clustered about the genital opening and fertilize the females as 

 they emerge. A full-sized gravid female is capable of producing 200 

 to 300 offspring, and retains its vitality throughout the birth of its 

 progeny. 



The life cycle of Siteroptes {— Pediculopsis) gramumm (Reuter) 

 is even more interesting than that of the preceding species. During at- 

 tachment to food the hysterosoma of the female swells from 100 to 500 

 times the original body volume and within this sack the eggs are formed 

 and develop into adult mites. In this species, however, there is a mass 

 birth marked by a breakdown of the hysterosoma, although an early 

 larva, nymph, or especially male may be extruded before the mass birth. 

 Only a few males are born, each brood containing at least one male. 

 Mating takes place within the sack before birth, as well as after birth. 

 Virgin females give rise to males, which have the haploid number of 

 chromosomes. This species, as well as Pyemotes, possesses heteromor- 

 phic males. 



Other members of this family are little known and apparently of no 

 economic importance. Banks 1915 stated that migratorial forms of a 

 Pygmephonis have been found on a mole, flies, and thrips, and Vitz- 

 thum states that Pygmephorus is carnivorous. Pygmephonis americanus 

 Banks has been reported as a "pseudoparasite" of Musca domestica and 

 Stomoxys calcitrans. Jacot 1936 has described a few east coast species 

 and given a key to distinguish the more common genera Pyemotes 

 {— Pediculoides) , Siteroptes (= Pediculopsis), Pygmephorus, and 

 Resinacarus. 



Pyemotes {— Pediculoides) ventricosus (Newport) is the causative 

 agent of the hay or grain itch. Normally it is an ectoparasite of various 

 insect larvae such as the Angoumois grain moth, Sitotroga cerecdella 

 (Olivier), the satin moth, Stilpnotia salicis (L.), the peach twig borer, 

 Anarsia lineatella Zeller, and of many other insects. When grain in- 

 fested with the parasitized grain moth larvae is handled at threshing, 

 in storage, or on the docks, these mites will attack man, especially in 

 hot weather when the need for moisture is great, and cause an intense 

 itching. All parts of the body are affected, although the arms and neck 

 are the regions usually attacked. As many as a thousand bites have 

 been recorded from one individual. They cannot burrow under the 

 skin or persist long on man, however. Swan 1934 describes the erup- 

 tions as follows: 'The wheals vary in size and form with different 

 subjects. They present, especially after rubbing, a raised whitish area 



