Evidence of sexual reproduction of woolly apple aphid, Eriosoma lanigerum, in New Zealand

Reproduction of the woolly apple aphid, Eriosoma lanigerum (Hausmann), can take place parthenogenetically or sexually when both host plants, apple (Malus domestica Borkh.) and elm (Ulmus americana L.) are available. Since elm is not commonly grown in New Zealand, E. lanigerum, a major pest of apple, is thought to reproduce only parthenogenetically here. During our studies between 1999 and 2003, different morphs of E. lanigerum have been observed on apple trees, which were studied in more detail in 2003 and 2004. In the laboratory, alates reproduced mainly sexual morphs with degenerated mouthparts. Oviparous females lived for 8.95 +/- 0.17 days (n = 20) and males lived for 7.1 +/- 0.12 days (n = 20). Both went through 4 moults, without feeding or changing body size. Oviparous female laid a single egg and died soon after oviposition. In addition to sexual morphs, shiny brown, oblong eggs were seen on apple leaves grown outside as well as in the glasshouse. As the numbers of eggs and sexual morphs on trees grown outside were less than on those grown in the glasshouse, we suggest that alates disperse into the natural environment searching for an apple or elm tree to continue the sexual reproduction while spreading the population.