ROW-TYPE OVIPOSITION IN NEODIPRION SAWFLIES AS EXEMPLIFIED BY THE EUROPEAN PINE SAWFLY, N. SERTIFER (GEOFF.)

Abstract

Many Neodiprion sawflies lay their eggs in a row in small pockets cut into the edges of the mature needles of various pines. These rows of eggs are remarkable for the regularity of the spacing between successive egg pockets. The regularity of egg spacing by N. sertifer is shown to arise from a stereotyped pattern of leg movements during the shift between the sites of successive egg pockets. Spacing is effected by two sets of leg movements, in each of which the three pairs of legs move forward in order from back to front. While the effective forward movement of all legs is the same, the total forward movement of the metathoracic legs is greater than that of the other legs by an amount equal to the length of an egg pocket. The metathoracic legs retrace their steps by this length as the initial incision for each new egg pocket is cut, evidently providing the force by which this incision is made. The grip-points of the legs are on the needle edge opposite to that receiving eggs, so that the wider the needle, the greater the proportion of leg length required to reach across it, and the smaller the proportion of leg movement reflected in the spacing between eggs. In this way egg spacing varies inversely with needle width. Observations on copulation, antennal movement, and related oviposition behavior are included.