Native natural enemies in Mediterranean melon fields can provide levels of pest control similar to conventional pest management with broad-spectrum pesticides

Pest control in Mediterranean open-field melon crops currently relies on repeated pesticide applications. A lack of IPM programs that take into account naturally occurring biological control agents in the crop could be due, in part, to a lack of knowledge of the natural enemies associated with melon and their pest control potential. We estimated the abundance of pests and natural enemies in fields managed with a conventional insecticide regime (CPR) and a 'no insecticide' regime (NPR), with all fields receiving fungicide applications (sulphur or triadimenol), as required. In a two-year study, six melon fields were sampled periodically during spring and early summer by visual observations of leaves and the extraction of arthropods from flowers using Berlese funnels. The most abundant phytophagous arthropods on melon leaves were thrips (38.9% of total counts), aphids (31.5%), spider mites (26.8%) and whiteflies (2.8%). Aphis gossypii was significantly more abundant in CPR than in NPR fields, whereas whiteflies and thrips had similar abundance in the two treatments. Spider mites were more abundant in NPR than in CPR fields. The main groups of natural enemies on leaves were Orius spp. (76.1% of total counts), phytoseiids (7.4%), predatory thrips (7.1%) and cecidomyiids (5.6%), and all were significantly more abundant in NPR than in CPR fields. The primary predators in flowers were Orius spp. (67.4%) and Aeolothrips spp. (32.6%), and both were significantly more abundant in NPR than in CPR fields. Orius spp. was inferred to be the primary biological control agent of aphids, as few aphids were mummified by parasitoids. The control of aphids by Orius spp. was probably mediated by apparent competition with thrips, which are a preferred prey of Orius spp. In summary, elimination of pesticides from the management regime enhanced the abundance of natural enemies in the melon crop, and natural biological control limited pest infestations in NPR fields as well as did broad-spectrum insecticides in CPR fields. Therefore, IPM strategies for melon production should consider conservation of natural biological control agents as an effective alternative to conventional regimes that rely primarily upon insecticides.