Production of Sexuals and Sex Ratios in Cryptomyzus Species in Relation to Dispersal and Host-Alternation (Homoptera: Aphidinea: Aphididae)
Guldemond, J. Adriaan; Tigges, Wouter T
The production of sexuals in aphids is not only influenced by day length and temperature, but also by aphid morpho Winged females of non host-alternating species of Cryptomyzus Oestlund 1922 give birth to relatively fewer male and more parthenogeneticmale (virginoparae), compared to wingless females. This might implicate differences in population structure encountered by these morphs, leading to an increase in mating of siblings and the maximization of the number of overwintering eggs produced by clones. This change of the sex ratio within a species is in agreement with theories on local mate competition. Non host-alternating species of Cryptomyzus living on herbaceous host plants were compared with a Cryptomyzus living on a woody host. In autumn the species on herbaceous plants produce, after a peak of sexuals, many parthenogenetic femalec that continue reproducing in mild winters. In contrast, the species on the woody plant ends the season with mainly sexuals and few parthenogenetic females; the latter are not likely to survive leaf fall. Further, the formation of sexuals differs considerably between conspecific hostalternating and non host-alternating forms. This flexibility in the production of sexuals is related to population structure, life cycle and host plant ecology.