Although Sitobion avenae (F.) was less fecund under sexual-inducing photoperiods it did not produce a significantly lower biomass of offspring than apterae reared under long daylength. The lower fecundity is due to the cost of developing the larger male embryos; at birth males were significantly heavier and denser than females. The primary sex ratio in S. avenae is approximately two females to one male but is equal in terms of biomass. Key-words: Sitobion avenae, sex ratio, aphids, reproductive cost
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Newton et al. (1987) studied this question.