A Histological and Bionietrical Study of Wing Development in the Grasshopper Melanoplus lakinus1,2

Abstract

Melanoplus lakinus Scudder (Orthoptera: Acrididae) is a brachypterous grasshopper of Arizona rangeland that occasionally shows macropterism. Wing development is similar histologically to that in holometabolans, although the epidermal cells are less attenuated in this species. The cells extend to the middle membrane and generally are not continuous with opposing cells. They become distorted after the procuticle is secreted. Nuclei elongate and migrate toward the middle membrane to varying degrees. The middle membrane may be as much as 3 µ thick. Granular molting fluid occurs in large quantity and is prevalent during the last half of each instar. Chromatolysis may occur in the last stage of growth in the hindwing. On the surface of the wing pads polygonal cuticular plaques change to “shingled” rows in the last 2 instars. Two characteristics of mitotic activity in wing pads are revealed: (1) mitoses occur in distinct bursts and at fluctuating low levels, and (2) the process begins while the epidermis is still attached to the endocuticle and continues after deposition of the procuticle. A mitotic burst could be followed from its initiation to its termination, over a 6-hr period, by successive sampling of the 4 wings of 1 specimen. Mitotic activity corresponds well with the increase in nuclei during each instar. There are no obvious structural differences between nymphs of brachypterous and macropterous adults. The regression coefficient of wing length on hind femur length increases significantly during most instars. The large increase in wing length of the macropterous form occurs in the last instar and deviates greatly from simple allometric growth. Thus far, mating of macropterous forms in cages has increased their frequency from less than 4% to 39% in the F1 generation.