The feeding punctures of 36 examples of forms of 19 species of aphids on their host plants were examined histologically. The types of plant penetration by the aphids' stylets were compared with the occurrence of pectinase in the saliva of these insects. In 17 cases the aphids penetrated only between cells, and all these insects possessed pectinase; in 9 cases the aphids penetrated directly through cells, and all these aphids lacked pectinase. In five instances aphids possessing pectinase penetrated directly through cells; and there were five examples, all possessing pectinase, that penetrated both between and through cells in the same probe. No aphid lacking pectinase penetrated between cells in the pectic middle lamella. I t is suggested that pectinase aids intercellular enetration by its hydrolytic action, but that the enzyme is not necessary when t i e aphid penetrates directly through cells.'Manuscript

Pectinase was found in the saliva of 23 species of aphids, one species of leafhopper, and one species of adelgid. The enzyme was not found in four species of aphids in their apterous form, and one species of psyllid, or in the saliva of the alate form of five species of aphids that contained pectinase in the apterous form. These results emphasize the need to consider each form of a species of aphid individually. The discussion considers similarities in the mode of tissue penetration by fungi and insects, and briefly the possibility that cell wall digestion by pectinase may facilitate the extraction of virus particles by insect vectors.

No abstract

In the laboratory, it has been found that females of R. pomonella (Walsh) mating frequently throughout their lives laid about twice as many fertile eggs as females allowed to mate only a few times during their first two weeks after emergence. However, mating had little effect on the total numbers of eggs laid. Females mating frequently averaged 395 eggs and 95% were fertile whereas those mating only a few times averaged 360 eggs and 46% were fertile.

A chromatographic technique demonstrated the presence of the enzyme pectin polygalacturonase in saliva ejected by Mysus persicae (Sulz.). The amount per gram of salivary gland was estimated to be 2.4 × 10−3 gm., a concentration presumed adequate to hydrolyze pectin in the cell walls adjacent to the feeding puncture of this species of aphid.