Photoperiodic determination of gynoparae and males of damson‐hop aphid Phorodon humuli

Abstract

Abstract. Sexual morph production in Phorodon humuli is controlled by daylength. Wingless aphids reared from birth in short‐day conditions (LD 12 : 12 h) and transferred when adult to long‐day conditions (LD 18 : 6 h) produce only gynoparae and males until death some 7 weeks later, whereas those reared in long days and transferred to short days produce 20% wingless parthenogenetic females, 50% gynoparae and 30% of males in an overlapping sequence. No winged morph capable of re‐infesting hop is produced. Less mature embryos are more sensitive to short days than older embryos because 100% of the former became gynoparae after 4 days of exposure of their mothers, and 59% when their mothers were exposed for the 4 days immediately preceding the birth of their offspring. Two days of exposure to short days switches 94% of young embryos from wingless to gynopara production when mature. The response to short days is irreversible. Wingless aphids reared from birth to adult in short days produce 30% fewer offspring than those reared to the same stage in long days and are male‐biased, with 76–78% of their offspring being male.