Concerted action needed among smallholders when using mass trapping of insect pests

Summary

Mass trapping with pheromones is an effective method for controlling insect pests. However, it is unknown whether this is effective for smallholders with typically fragmented holdings, as local depletion by traps may be (over)compensated by the attraction of male moths from surrounding fields. This was tested on a major pest in eggplant, the shoot and fruit borer moth (Leucinodes orbonalis). In a two-year field experiment in Bangladesh, moth catches and fruit infestation were compared across isolated fields with a grid of 4 (2 by 2) traps, 24 (4 by 6) traps (10 m distance between traps) and farmers’ practice fields (fields without traps but with spraying). Additionally, in one year, three networks with respectively 22, 28, and 40 traps were installed in scattered but nearby fields to compare results to the 24–trap fields. Across each season, moth catch per trap per week was three times higher in the 4–trap fields than in the 24–trap fields or the networks. Fruit infestation was comparable between 4–trap fields and farmers’ practice fields in both years, while fruit infestation in 24–trap fields was 25 percentage points lower, showing effective local depletion of male moths only occurred in 24–trap fields. Trapping with networks of 22 − 40 traps yielded comparable results to the 24 contiguous traps providing evidence that loosely organized networks of multiple traps could also be effective. Given their plots are generally much smaller than 2400 m², smallholders can only make trapping effective if they take concerted action.