Assessment on the potential decrease of insecticide treatments against aphids in 'HoneySweet' plum (Prunus domestica (L.)) plantings

‘HoneySweet’ transgenic plum is protected against the detrimental Plum pox virus (PPV) by a RNA interference mechanism. Field trials performed in different PPV endemic European countries demonstrated that its use represents an efficient strategy for PPV containment. Regulatory authorities in the US have found no safety concerns and approved ‘HoneySweet’ for cultivation. Fruit growers are facing safety issues related to the use of pesticides and are obliged to comply with EU requirements to reduce their use. We have raised the question as to whether some treatments against aphid vectors might be avoided in ‘HoneySweet’ plantings. Aiming to evaluate the requirements, a field trial including ‘HoneySweet’ (Prunus domestica (L.)) and two conventional P. domestica plums cultivars (‘Stanley’ and ‘Reine Claude d’Althan’) was established in 2013. Since ‘HoneySweet’ cannot be naturally infected with PPV by aphids, the question about the use of insecticides arose. Through two years of observations, the situation appeared complex because avoiding some treatments raises questions of direct damages done by aphid feeding and, more importantly, of controlling other important insect pests, i.e., Laspeyresia funebrana (Tr.). Therefore, both pests were monitored at the same time. Our results revealed that a reduced number of insecticide treatments did not lead to significant aphid damage due to their feeding on young shoots and leaves. On the other hand, the flight curve of Laspeyresia funebrana Tr. partly overlaps those of aphids and, consequently, treatments with insecticides are necessary to control this pest, regardless of a need to control aphids. However, the identification of periods when the flight curve of the two pests do not overlap might allow avoiding some treatments. Interestingly, we have identified such a period in September, when the aphids are resuming their flight for a short period and hence, under the conditions of our study, a slight decrease in the number of treatments with insecticides could be possible.