No abstract

Commonly three species of aphids infest oats in New Brunswick, Canada. These aphids are Rhopalosiphum padi (L.), Macrosiphum avenae (Fab.), and Rhopalosiphum maidis (Fitch), named in the order of their abundance. Over a 5-year period (1959–1963 incl.) infestations varied from peaks of less than 1 aphid to 250 aphids per tiller. The aphids infested the crop for approximately 7 weeks, from the time the plants were 3 in. high until the panicles had emerged. When the panicle stage was reached (normally in the fourth or fifth week of the infestation), a winged generation of aphids developed and dispersed from the oats, resulting in an abrupt decline in the population.

From similar initial populations, aphid infestations became higher in herbicide-treated areas of oats than in similar untreated areas. Fewer coccinellids were present in these treated areas. The inclusion of an aphicide with the herbicide applications held subsequent populations of aphids to the level of those in untreated plots. Although populations as high as 250 aphids per tiller occurred, no reduction in yields of grain or straw was found in 1962 or 1963.

Fifty-eiqht species of aphids frorn a wide range of hust plants, one l d o per species frorn Vilir sp., m d n pqillid from rliriicr rugma have been exarnindfor their salivary abiEity to hydrolyze carbaxymelh I cellulose (CMC) substrates. Most of these insects, when allowed to prohe a d s e c r e t e P X~~M into CCMC-filled parafilm "sachets", reduced the CMC to glucosc and sometimes to glucose and cclIobiow. The presence of this cellulose-hydroIyzing factor varied among species, and within species according to rnorph, season, and hwt plant from which the insect culture had been derived. Thc behavior of the insects on the sachets resembled the characteristic "test probing" of aphids described by many authors. I t is suggested that salivary components secreted during such test probes play a role in host plant selection and subsequent exploitation.

Extracts of 12 species of aphids differed in their capacities to reduce the viscosity of methyl cellulose (MC) substrates. The activity of these extracts varied from as much as 60% reduction of viscosity in 48 hours, when the species Myzus cerasi Fab. from Prunus pennsylvanica L. was used, to zero change when the extracts were from Tuberolachnus salignus (Gmelin) from Salix babylonica L. Extracts from the remaining 10 species reduced the viscosity of MC substrates by about 25% in the same period. In many cases the activity of these extracts was almost doubled if the extract was heated in a boiling water bath for 5 minutes prior to being incubated with the MC; in only a few cases was it reduced. The plant host on which the aphids were cultured appeared to influence both the rate of activity and the effect of heating.