Sexual morph production by apterous and alate viviparous Acyrthosiphon pisum (Harris) (Homoptera: Aphididae)

Production of sexuales by wingless and winged individuals of the pea aphid Acyrthosiphon pisum (Harris) was monitored at two constant temperatures and a series of photoperiods using three different clones. Temperatures were either 15 or 20 °C and photoperiods ranged from 15 h light: 9 h dark to 10 h light: 14 h dark. Wingless grandparents from each clone were placed in the constant conditions and allowed to produce a parental generation of wingless and winged aphids. These were maintained under the same conditions until adulthood. Their offspring consisted of viviparae, oviparae, and males in varying proportions. The three clones differed in relation to the photoperiods at which particular proportions of the morphs were produced but all exhibited the same sequence of change in proportion with declining photoperiod. At successively shorter photoperiods the proportion of males among total offspring of wingless parents increased to a maximum of 73% but declined again to near zero at the shortest photoperiods. The proportion of oviparae among the female offspring of wingless parents also increased initially from zero to a maximum of 100% and then declined again to not less than 43%. Winged parents produced oviparae almost exclusively at all photoperiods short enough to induce production of sexuales.