Injuries to plants caused by insect toxins. II

Abstract

The author's first review of the literature on plant diseases caused by the toxic feeding of insects included the available refer? ences up to and including 1938. This supplement, having been de? layed for various reasons, brings the review up to the end of 1950. The order of presentation has been slightly changed to avoid arbitrary separation of effects produced by one group or species of insect. For example, the effects of leafhopper feeding, whether they be leaf spotting, hopperburns or systemic effects, are all in? cluded under the heading " Cicadellidae ". An exception to this is the section on insect galls. The whole field of inquiry suffers somewhat from deficiencies in clearly defined criteria whereby toxins can be established as causal. Many writers simply describe symptoms, without discussing the nature of the causal entity. Others have difficulty in separating traumatic effects from those caused by toxins. These two are probably often closely associated. Several careful studies, how? ever, seem to have established the toxic nature of insects' feeding. With some groups of insects, notably the Capsidae, the effect of the insects' feeding appears to be so violent that mere trauma un? doubtedly can be discounted. These groups appear to be increas? ingly important on many culitvated crops. Certain fundamental considerations appear to have received some attention. The similarity of certain feeding effects to those achieved by hormonal action, the effect of host feeding sequence in conditioning secretions, and the similarity between certain gallproducing substances and neoplasmagenic substances indicate that this field of inquiry may contribute to the study of neoplasms as well as to the broader field of evolution.