Laboratory, semi-field and field studies to evaluate the effect of pesticides on psyllids

Cacopsylla pyri and C. melanoneura are considered important pests for pear and apple orchards in north Italy: the first caused direct damages on pear plants while the second is involved in transmission of apple proliferation phytoplasma. Every year several insecticides are required in order to control these psyllids. Data obtained from laboratory, semi-field bioassays and field trials are important to develop new IPM strategies. The present work reports three methods to evaluate the effect of pesticides on psyllids. A baseline was determined for C. pyri. The used method consisted in treating pear leaves by immersion into pesticide solutions, and rearing larvae of C. pyrion holding cells. The mortality of psyllids was assessed after 72 hours. The efficacy and the persistence of pesticides were then evaluated by semi-field bioassays. Overwintering adults and young instars of C. melanoneura were put on treated potted apple plants, which were isolated with cloth cages, at three different timing (1 hour, 7 and 14 days after the pesticide treatment). Adult survival was recorded after 1, 3 and 7 days after their exposure to the pesticide, while young instar survival was recorded 7 days after they were placed on plants. Finally pesticides were evaluated in field trials to assess both efficacy and side-effects. The experimental design was based on randomized blocks in a commercial apple orchard. Beating method was used to assess the overwintering adult survival of C. melanoneura, while samples of shoots and leaves were collected to count the number of eggs and young instars of psyllids and to assess the presence of beneficials.