Impact of native forest remnants and wild host plants on the abundance of the South American fruit fly, Anastrepha fraterculus in Brazilian apple orchards

In Parana, southern Brazil, apple orchards are commonly bordered by highly biodiverse Atlantic Forest remnants. The main insect pest in these orchards is the highly polyphagous South American fruit fly, Anastrepha fraterculus. Technical advisers recommend that farmers remove wild host plants of A. fraterculus around orchards, which is at odds with the need for forest conservation. We thus investigated whether the presence of Atlantic Forest remnants and A. fraterculus host plants surrounding commercial apple orchards affect A. fraterculus populations in apple orchards in Parana, southern Brazil. For this purpose, we monitored A. fraterculus using McPhail traps in a total of 67 100 m × 200 m apple orchard plots that differed in their adjacent landscape (forest with A. fraterculus host plants, forest without host plants, open areas). In total, we captured 6412 Anastrepha fruit flies during four growing seasons. At the time when the apple fruits were susceptible to A. fraterculus, the probability of occurrence (i.e. of presence or absence) of A. fraterculus did not differ among the adjacent landscape types and was not affected by the presence of specific host plants. Its abundance in traps where at least one individual was found was also not affected. In contrast, at the time when the apple fruits were absent or not susceptible to A. fraterculus, A. fraterculus probability of occurrence was significantly higher in plots adjacent to open area than in plots adjacent to native forest remnants and intermediate in plots adjacent to native forest remnants with A. fraterculus host plants. At that time, its probability of occurrence and its abundance increased only with the presence of Psidium cattleyanum in these forest remnants. These results indicate that forest remnants had a limited impact on A. fraterculus abundance in orchards and do not support the recommendation to indiscriminately remove wild host plants adjacent to apple orchards.