Designing an exclusion net for Grapholita molesta (Busck) (Lepidoptera: Tortricidae)

Different mesh sizes have been used for fruit protection and pest exclusion against various pests, but no information or experimental results concerning exclusion of Grapholita molesta (Busck) (Lepidoptera: Tortricidae), Oriental fruit moth, were found in the available literature. There is no accepted methodology to assess the efficacy of insect-proof screens, but in theory the mesh pore size (the space between warp threads) should be equal to or smaller than the thorax width of the insect. Thorax diameter has been considered as the most suitable dimension to take into account, because the thorax is the most rigid part of the insect body. A published reference providing the thorax width of Oriental fruit moth was not found, so specimens in the Canadian National Collection of Insects (CNC) at Agriculture and Agri-Food Canada (AAFC) were measured. The average size of the thorax of the wild population was 1.61±0.16mm (range 1.16 to 2mm). We performed additional measurements of Cydia pomonella (thorax width 1.87±0.32mm) and did comparisons with a recently tested multiple pest exclusion net in Quebec. In conclusion, we propose a screen with pore size 1.6mm or smaller for pest exclusion of Grapholita molesta.