Aploneura lentisci (Homoptera: Aphididae) and its interactions with fungal endophytes in perennial ryegrass Lolium perenne)

Aploneura lentisci Pass. is endemic to the Mediterranean region where it is holocyclic, forming galls on its primary host, Pistacia lentiscus and alternating over a 2 year period between Pistacia and secondary hosts, principally species of Graminae. This aphid is widely distributed in Australia and New Zealand on the roots of its secondary hosts, ryegrass (Lolium spp.) and tall fescue (Schedonorus phoenix) where it exists as permanent, anholocyclic, parthenogenetic populations. The aphids produce copious amounts of flocculent white wax which likely protects them from soil moisture extremes, microbes and predators. Winged morphs have been trapped in both Australia and New Zealand but have not been observed in field populations sampled from either country. Mobile young nymphs can be found on herbage and it is hypothesized these may be wind dispersed. Two pot trials were conducted to investigate aphid populations on roots of perennial ryegrass infected with three strains of the symbiotic fungal endophyte Epichloë festucae var lolii. These obligate biotrophs protect their host grasses from certain species of insect herbivores via the production of alkaloids. In both pot trials, aphid numbers were lowest on plants infected with endophyte strain AR37 at all sampling times. In plants infected with the common toxic strains, aphid numbers overall were lower than on uninfected plants or those infected with strain AR1, but numbers did not always differ significantly from these treatments. Populations on AR1-infected plants were occasionally significantly higher than those on endophyte-free. There was no discernible seasonal pattern in populations per plant or root mass. Cumulative foliar growth was reduced in AR1 and Nil treatments relative to AR37 due to A. lentisci in both trials and root dry weight was reduced in one trial. In four Petri dish experiments survival of A. lentisci on plants infected with AR37 declined to very low levels after an initial phase of up to 19 days during which time aphids fed and populations were similar to those on plants without endophyte. Aphids on AR37-infected plants became uncoordinated in their movement and developed tremors before dying suggesting a neurotoxin was responsible for their mortality.