Positive effects of an arbuscular mycorrhizal fungus on aphid life historytraits

Two generations of two aphid species (Myzus ascalonicus and M. persicae) we re reared on Plantago lanceolata plants, with and without root colonization by the arbuscular mycorrhizal fungus, Glomus intraradices. Life history tr aits of the aphids measured were nymphal development time, teneral adult we ight, growth rate, total fecundity, adult longevity and duration of postrep roductive life. For both aphids in both generations, mycorrhizal colonizati on increased aphid weight and fecundity, while other traits were unaffected . The increases were consistent between generations. In a second experiment , M. persicae was reared on plants with and without the fungus, under varyi ng N and P regimes. The results of N addition were inconclusive because the re was high aphid mortality. However, under P supplementation, positive eff ects of the mycorrhiza on aphid growth were seen at low and medium P levels , while at high P levels these effects disappeared. The positive effects of mycorrhizal colonization reported here are contrary to the majority of pre vious studies with chewing insects, which have reported negative effects. A number of possible mechanisms for this apparent discrepancy are discussed.