An interesting Principle in Economic Entomology and some Useful Applications

Extract

In the course of my investigation of the serious pest of palms, Oryctes rhinoceros, it was observed that a great proportion of the larvae work their way several inches below the floor of the manure pit in which they thrive, for pupation; and it occurred to the writer that attempts should be made to prevent the return journey by the insects as adults. Now the larvae and adults are of about equal girth, but as the former are soft-bodied they can squeeze themselves through holes which are impassable for the rigid-bodied adult. A sheet of expanded metal with meshes 12 by 24 mm. will let the larvae through but not the adults, and therefore should prevent the escape of beetles from manure pits in which the floor has been carefully covered with this metal. How far the idea will be of practical application in the control of the pest under the varying conditions in which manure is stored remains to be seen, but this preliminary note is written to drew attention not to any remedy but to the principle itself, which is important and has a wider application than to the insect from the study of which it was first derived. It has been found, for example, that it operates in the case of flies also, the holes through which the maggots may be able to pass being impassable for the adults. In the case of the house-fly a perforated zinc sheet will let the maggots through, but not the adults, and a trap is under trial in which the flies are attracted to suitable material and the maggots resulting from oviposition have to pass for pupation through a perforated zinc sheet into a chamber from which the flies cannot escape. The success of this trap as well as of the lines of attack now opened up against Oryctes rhinoceros remains to be seen, but the principle is, I believe, of sufficient importance for early attention to be drawn to it in the pages of this journal.