INTRODUCTION It is considered that Aphidoidea evolved in the Carbo- niferous period, approximately 280 million years ago (Dixon, 1998) and since then they have followed several evolutionary pathways. One evolutionary trajectory is cyclical parthenogenesis, the alternation between an annual sexual and several asexual generations, which first appeared in the lower Permian (Heie, 1967; Dixon, 1998). This reproductive strategy combines the advan- tages of sexuality (i.e. creation of new genotypes, elimi- nation of deleterious mutations) and parthenogenesis which involves the telescoping of generations, providing high rates of population increase. A widespread phe- nomenon in Aphidoidea, however, is the partial or total loss of sexuality. It is often observed within species, e.g. in certain populations of a species or in genotypes of a given population. The number of species thought to be totally parthenogenetic is rather small (Blackman & Eas- top, 2000). This intraspecific variation in reproductive strategy has been studied in several species of the family Aphididae, e.g. Aphis gossypii Glover (Takada, 1988), Sitobion avenae Fabricius (Dedryver et al., 2001), Rhopa- losiphum padi (L.) (Simon et al., 1991) and Myzus per- sicae (Sulzer) (Blackman, 1971; Margaritopoulos et al., 2002). Four life cycle categories have been described. There are genotypes (holocyclic) with a sexual phase which produce both males and mating females (in Aphididae, as opposed to Adelgidae and Phylloxeridae, all parthenogenetic females are viviparous and mating females are oviparous), while others (anholocyclic) are permanently parthenogenetic. There are also genotypes with a partial loss of sexuality, which produce mainly parthenogenetic females along with a few males (andro- cyclic) or with some males and mating females (interme- diates). The genotypes with a sexual phase and those with a partial loss of sexuality are not reproductively isolated one from each other; they experience at least some gene flow (Blackman, 1972, Dedryver et al., 1998; Simon et al., 1996, 1999; Delmotte et al., 2001). The sexual phase is triggered by environmental changes, with photoperiod and temperature being the most crucial factors (Hille Ris Lambers, 1960; Lees, 1966; Kawada, 1987). Photoperiod provides the timing mechanism for sexual morph production. According to Blackman (1974), when genotypes with a sexual phase occur, their photoperiodic response is tuned to local con- ditions. Temperature often interacts with photoperiod modifying its effect. At temperatures above 25°C, the production of sexuals is inhibited in most aphid species (see Kawada, 1987 and references therein). Temperature is also responsible for the regional pattern of life cycle variation observed in aphids (Blackman, 1974; Rispe et al., 1998; Rispe & Pierre, 1998; Dedryver et al., 2001). The effect of photoperiod in the production of sexual morphs by genotypes with a sexual phase has been well studied in many aphid species, e.g. M. persicae (Matsuka Eur. J. Entomol. 103: 337–346, 2006 ISSN 1210-5759 Effect of temperature and photoperiod on the life cycle in lineages of Myzus persicae nicotianae and Myzus persicae s. str. (Hemiptera: Aphididae) DESPOINA POUPOULIDOU, JOHN T. MARGARITOPOULOS*, THIRESIA E. KEPHALOGIANNI, KOSTAS D. ZARPAS and JOHN A. TSITSIPIS Laboratory of Entomology and Agricultural Zoology, Department of Agriculture, Crop Production and Rural Environment, University of Thessaly, Nea Ionia 384 46, Magnesia, Greece Key words. Myzus persicae, Myzus persicae nicotianae, males, mating females, sexual morphs Abstract. Male production was examined in 70 Myzus persicae s.str and M. persicae nicotianae clonal lineages at 17°C and 10L : 14D. Sixty nine were characterised by a partial loss of sexuality (androcyclic producing few males, and intermediates producing some males and mating females), and one was found to be permanently parthenogenetic. High within and between lineage variation was detected. Most (81%) of the clonal lineages produced few males (0–5 males per parent) and only 6% had male production (10–16 males per parent) comparable to that (12–23 males per parent) of seven lineages with a sexual phase (holocyclic) which were examined under the same conditions. The length of prenatal exposure to 10L : 14D increased the production of males. Continuous rearing under 10L : 14D at 12°C adversely affected male production in another intermediate clonal lineage. Temperature was found to affect the production of sexuals and to modify the short day photoperiodic response. The production of males and mating females was higher at 12°C than at 17°C in most of the 20 aforementioned clonal lineages with a partial loss of sexuality. Six lineages were permanently parthenogenetic at 17°C, but two of them produced a few males and the other four a few males and mating females at 12°C. Seven lineages which produced a few males at 17°C, also produced some mating females at 12°C. Lastly, photoperiod simi- larly affected the production of sexuals in two of the aforementioned clonal lineages, one with a sexual phase and one intermediate, although the regimes for the peak of sexuals were different. In both lineages, however, males appeared in a 0.5–1 h shorter scoto- phase than mating females. 337 * Corresponding author; e-mail: jmarg@uth.gr