Photoperiodic determination of the male and female sexual morphs of Myzus persicae

Abstract

The chronology of the photoperiodic determination of sexual morphs in holocyclic Myzus persicae was studied in the laboratory by transfer of synchronized batches of aphids between long-day (16 hr) and short-day (10 hr) régimes at a constant temperature of 20°C. The length of exposure to the short-day régime was measured in terms of the number of long dark-periods received by the aphids. The photoperiodic response extended over four generations (P, G 1, G 2, and G 3 respectively). When P generation aphids were given short days from the fourth instar, alate viviparae and males appeared successively in generation G 2, oviparae in G 3. Increasing the number of long dark-periods received during the development of G 2 embryos had a cumulative effect on the number which developed into alate viviparae. Determination of all the first-born G 2 aphids as alatae occurred only if their mothers had been exposed to the short-day régime throughout larval development. Alate viviparae gave birth to oviparae if they received a minimum of 4 long dark-periods, starting from a late stage in their embryonic development. The critical stage for ovipara determination in the G 3 embryo was on the sixth or seventh day after ovulation, more than half-way through embryonic development. G 2 aphids were determined as males before ovulation if their parents received 4 (in some circumstances only 3) long dark-periods. In the clones studied, male determination, once initiated in the G 1 parent, could not be reversed by later back-transfer to the long-day régime.