Male production by apterous viviparae of the aphid Myzus persicae temporarily exposed to different scotoperiods

Male production by apterous viviparae of a holocyclic biotype of the green peach aphid, Myzus persicae, was induced by pre-natal and/or post-natal exposures to a long-night regime of 15 h dark per diem. When the apterae were exposed to three or more long nights immediately after birth and they subsequently developed under a short-night regime of 8 h dark per diem, they produced females (mostly alate viviparae) during the first 8–10 days of reproduction and a high proportion of males thereafter. When the apterae were exposed to two long nights immediately before their birth and to short nights thereafter, they produced relatively few females (mostly alate viviparae), and males were deposited already after 4–6 days of reproduction, i.e. 16–18 days after the first exposure to the long nights. The proportion of males among the progeny of these apterae was highest when the two prenatal exposures comprised scotophases of 11–15 h; under such long-night regimes many aphids switched to producing males exclusively. To achieve this effect, the two long scotophases had to be separated by a photophase of more than 1–2 h. Fewer males were produced and most of the apterae reverted to the production of females (apterous viviparae) when the duration of the two prenatal scotophases was 9 h 45 min-10 h 30 min, or 18 h and longer.One long night of 15–39 h could also induce temporary male production if the aphids were exposed to it late in the 4th larval instar or as teneral adults.