J. A. DAVIDSON’s research while affiliated with University of Maryland, College Park and other places

Life histories were studied for 9 aspidiotine species, one in the greenhouse and 8 in the field. Observations on the latter were made weekly when possible. The time of appearance and duration of each stage were determined and data were compiled for the species. As a result, seasonal history charts are presented and discussed for Abgrallaspis ithacae (Ferris), A. townsendi (Cockerell), Aspidiotus cryptomeriac Kuwana, Diaspidiotus liquidambaris (Kotinsky), D. mccombi McKenzie and Hemiberlesia lataniae (Newstead); seasonal development is discussed for Aspidiotus nerii Bouché, “Diaspidiotus” osborni (Newell and Cockerell) and Hemiberlesia diffinis (Newstead). Information on predators and parasites includes parasite emergence times. There are keys to immature and adult stages and to 1st and 2nd instars of the 9 species studied. Morphological features are discussed in detail for all immature stages and are illustrated. Specific characters are discussed for all immature stages and are illustrated for all 1st- and 2nd-instar males and 2nd-instar females. Characters of the immature stages indicate that diffinis belongs in Hemiberlesia Cockerell instead of Abgrallaspis Balachowsky and that osborni is probably misplaced in Diaspidiotus Cockerell. The correct generic placement of osborni cannot be determined until the immature stages of additional species of the Aspidiotini are studied.

Sexual dimorphism in 2nd-instar diaspidids has been shown by few workers. Bennett and Brown (1958) reported color differences between both eggs and crawlers of males and females of Pseudaulacaspis pcntagona (Targioni Tozzetti), and sexual dimorphism was reported in the 1st instar of Geodiaspis arundinariae Tippins and Howell (1973). In early 1971, after comparing all stages of 16 aspidiotine species, Stoetzel discovered a setal pattern that distinguished the sex of all stages at the tribal level. The following species were studied: Abgrallaspis ithaeae (Ferris), A. townsendi (Cockerell), Aonidiella taxa Leonardi, Aspidiotus cryptomeriae Kuwana, A. nerii Bouche, Diaspidiotus liquidambaris (Kotinsky), D. mecombi McKenzie, D. osborni (Newell and Cockerell). Hemiberlesia diffinis (Newstead), H. lataniae (Signoret), Melanaspis obscura (Comstock), M. smilacis (Comstock), M. tenebricosa (Comstock), Pseudaonidia paeoniac (Cockerell), Quadraspidiotus juglansregiae (Comstock), and Q. perniciosus (Comstock).

A 3-year study of the life history variations of the obscure scale, Melanaspis obscura (Comstock), has revealed asynchronous development of this insect on white oak and pin oak in Maryland. A figure is included which gives the occurrence of all stages on both hosts. Explanations are given to support the premise that the 2 populations are reproductively isolated, and the expected distribution and collection sites of the obscure scale are shown. Attention is given to development of the adult female cover as a means of predicting crawler emergence for use by those interested in control of the obscure scale.

The biology of Melanaspis obscura (Comstock) (Homoptera: Diaspididae) was investigated using a population on pin oak in Prince Georges County, Maryland, in 1968-69. M. obscura is a univoltine species which overwinters on pin oak as 2nd-stage males and females. A figure is included which gives the seasonal occurrence of all stages. The obscure scale was found to be parasitized by 8 species of Hymenoptera and preyed upon by 14 species of mites and 3 species of coccinellids. Nine species of mites believed to be free living were found associated with the scale. The pink scale-fungus, Nectria diploa Berkeley and Curtis, was found attacking M. obscura. Crawler transfers from pin oak to red maple, silver maple, grape, and hickory were unsuccessful although the obscure scale is recorded in the literature from these hosts. The sexes of slide-mounted early 2nd instars can be distinguished, since females have a pair of submedian clusters of 7-14 long microducts each on the dorsum of the cephalic region just anterior to the prothorax, while males have a row of 10-16 long microducts on each side of the dorsal margin extending from the metathorax through the 1st abdominal segment.