Yellowing, morphology and behaviour in sexually mature gynandromorphs of the desert locust Schistocerca gregaria

The morphology, colouration and sexual behaviour of two gynandromorph adults of the desert locust Schistocerca gregaria Forskål are described. In each of these specimens, the left half of the external genitalia has male characteristics and the right half has female characteristics. Yellowing of the epidermis occurs to different degrees in normal sexually mature male and female adult S. gregaria under crowded conditions. Two hypotheses are known to explain this phenomenon. One suggests involvement of a sex‐hormone/receptor complex, whereas the other proposes different sensitivities of the epidermis to the same hormonal environment. To examine which hypothesis is more likely, one gynandromorph adult is kept under crowded conditions and the other is maintained under isolated conditions. In the former, the left half of the body turns bright yellow, as in a sexually mature crowded male, and the right half is brownish with little yellowing, as in a sexually mature crowded female of the same age. The bilaterally divided body colouration may support the second hypothesis. In the second gynandromorph, which is isolated after adult emergence, the body colour remains brownish. Upon sexual maturity, this individual is kept together with normal male or female adults for behavioural observations. It attempts to mount a female but is approached and mounted by males.