PROGRESS REPORT ON THE EUROPEAN CORN BOEER 19 
In some cases it seems that the species of plant selected as food 
or as shelter depends more upon its location with reference to other 
heavily infested plants or plant material than upon its character as 
a plant. The protection afforded to gravid females also appears to be 
a determining factor in some instances, since eggs are deposited 
freely upon certain large-leaved plants, rhubarb for example, which 
afford protection to the females during the day. Moreover, some 
plants in which the larvae are not known to feed are occasionally 
utilized for egg deposition, as will be shown in this discussion. 
In New York, Pennsylvania, Ohio, and Michigan, and in Ontario, 
the infestation to date has been confined mostly to 1 corn, with com- 
paratively slight infestation in the more susceptible weeds. Occa- 
sional borers ako have been found in some of the economic plants in 
the Lake Erie region and in Ontario. During 1923 and again in 
1924 two commercial fields of broomcorn in western New York sus- 
tained infestations which were nearly equal to those of field corn in 
the vicinity. Probably the intensity and variety of infestation in 
susceptible weeds, vegetables, field crops, and flowering plants eventu- 
ally will increase in these areas if the insect should become more 
numerous. It is possible also that the comparatively restricted list 
of host plants in these areas, as compared to New England, may be 
influenced by the fact that in New England two generations usually 
occur annually, whereas in the more western areas and in Ontario 
only one generation has yet been observed, except in favorable sea- 
sons when a few individuals of a second generation have developed. 
Under two-generation conditions the insect begins its feeding activity 
much earlier in the season than where but one generation occurs, and 
continues feeding actively throughout a longer total period for the 
season. Therefore it is able to use as hosts during the early part of 
the season, and again during the late season, many plants which are 
not available in an attractive or susceptible stage of growth during 
the period when the single-generation adults and larvae are most 
active. 
NEW ENGLAND 
In this section, up to January 1, 1924, the European corn borer has 
been found inhabiting a total of 215 different species and varieties 
of plants, some of which apparently serve primarily as shelter rather 
than food for the borers. 
The relative degree of susceptibility of these host plants to P. 
nubilalis, and the parts attacked, are shown in the following list 
(Table 1) compiled for the New England area. In genera where two 
or more species were found to be hosts of P. nubilalis, usually only 
the generic name is listed. 
