RESISTANCE MECHANISMS IN DYSAPHIS PLANTAGINEA. PRELIMINARY INVESTIGATION ON THE DETOXIFYING ENZYMES

The apple rosy aphid, Dysaphis plantaginea (Passerini), is a serious pest in pome orchards. Insecticide applications of to reduce damages are usually a need and are based on pre- and / or post-flowering treatments. The secondary host of this aphid has no agricultural interest so, differently from other species like Myzus persicae (Sulzer) and Aphis gossypii Glover the summer generations are not treated. This lower selection pressure is certainly the main reason for the quite rare reports of resistance in D. plantaginea. However, following specific control failure reports, it was considered wise to make a preliminary survey on the activity of enzymatic systems of D. plantaginea, that in other aphid species are known to be involved in insecticide resistance. In spring 2008 two populations of D. plantaginea were collected: the first in a commercial orchard with insecticide control failures, the second from an apple tree in an untreated garden far away from commercial fruit orchards. Spectrophotometric and fluorimetric techniques have been used to measure the activity of the following enzymatic systems: esterases, glutathione S-transferases, monooxygenases and acetylcholinesterases. Preliminary results indicate that between the two populations: • there are no significant differences in the activity total esterase; • also the activity of glutathione S-transferase is very similar; • acetylcholinesterase is inhibited equally in the presence of a dimethycarmabate diagnostic concentration that in M. persicae can distinguish among resistant than sensitive specimens; • there are differences in monooxygenase activity: such activity is higher in the specimens from the population that survived the treatments. These observations are consistent with literature data obtained on some French populations several years ago. Further investigations will be needed to clarify the role played by monooxygenases in the sporadic cases reported of treatment efficacy reductio