Host range expansion of diamondback moth,Plutella xylostella to peas:Effects on its parasitoids in Kenya

摘要

A population of the diamondback moth(DBM)，Plutellaxylostella L.，was recently found on sugar snap peas and snowpeas(Pisum sativum L.)in the Rift Valley in Kenya，causing heavy damage. The impact of this host range expansion on the interaction with associated parasitoids was investigated. In laboratory experiments，we studied the role of host plants in host location of the indigenous Diadegma mollipla(Holmgren)，regarded as a generalist，and the exotic Diadegma semiclausum(Hellen)，which is considered a specialist.Host location was tested in a Y-tube olfactometer.Results showed that the specialisation of D. semiclausum is mediated by host plant signals associated with crucifers.which are not encountered in peas. In contrast，D.mollipla does not use crucifer volatiles as primary cues for host location. In field studies，peas provided an enemy-free space for DBM.Local parasitoids occurred only sporadically and in very low numbers on DBM on peas. The release of D.semiclausum into the study site led to a reduction of DBM only in kales.With strong competition on kales，D.mollipla was assumed to find a niche in peas.However，it did not occur in larger numbers in peas. In conclusion，we demonstrated that the host plant had a strong influence on host location of the specialist parasitoid. The inclusion of a new host plant into its feeding repertoire enables the herbivore host to avoid enemy attack.