Environmental and Genetic Control of Wing Morph Determination in Three Subtropical Populations of a Cricket, Modicogryllus confirmatus (Orthoptera : Gryllidae)

The effects of photoperiod and temperature on the relative frequency of short-winged (SW) and long-winged (LW) morphs of a cricket, Modicogryllus confirmatus WALKER, were examined in three subtropical populations (Naha : 26.1°N ; Yonaguni : 24.3°N and Ishigaki : 24.2°N) from Okinawa Prefecture, Japan. The genetic basis of wing morph determination was also studied by crossing different wing morphs of crickets recently collected or selected over 30 generations with respect to wing length. The frequency of SW adults was relatively high at a short photoperiod (12L-12D) and low at longer photoperiods (13L-11D to 16L-8D) in the Naha and Yonaguni populations. Photoperiod did not influence wing morph determination in the Ishigaki population. No significant difference was observed in the frequency of SW adults between 25℃ and 30℃ in any population. The three populations showed geographic variation in wing morph ; the frequency of SW individuals under short-day conditions tended to be higher as the latitude increased. After mass selection over 10 generations the frequency of SW adults in a SW selected line increased substantially, whereas it remained at a low level in a LW selected line. Crossing experiments indicated that wing morph was under polygenetic control. Based on these results, we discuss the evolutionary significance of wing dimorphism in this subtropical insect.