Are Bactocera oleae adult traps really useful? Are captures correlated with infestations? Which captures are intervention or alarm thresholds?

In IPM of olive groves, setting traps to monitor adult populations of Bactrocera oleae (Rossi), olive fruit fly, either males by pheromones or both sexes by yellow and food attractants, is a practice still widely suggested, sometimes considered mandatory, by the phytosanitary services of many Mediterranean countries, Italy first. Despite this, rarely an intervention or alarm threshold based on adult catches is indicated and, when it occurs, the alarm threshold to start sampling drupes is rather low (1-3 adults/trap). Thanks to our decades-long investigations on the efficacy of different methods of controlling B. oleae infestations, by analysing a large amount of data, we have sought a correlation between the average catches of three pheromone traps and the active infestation detected in the same untreated plot in the same week, and after one and two weeks. The correlation between the captures of males and the infestation levels of the three weeks considered, resulted very low, not allowing the definition of both alarm and intervention threshold.. Consequently, captures of adults of B. oleae, a monophagous insect that tends to remain in the olive groves even in unfavorable environmental conditions, suspending its oviposition, are useless in assessing the risk of attack. Therefore, attention should be addressed towards direct monitoring of the levels of infestation in the drupes, preferably with simplified methodologies (sequential sampling, external observation of the drupe) which can certainly provide more reliable and useful data than captures of adults.