Selected flowering plants as a habitat for pollinators and natural enemies in field margins of a watermelon crop—implications for crop yield

The practice of field margins management using mixtures of selected plants to provide habitats for pollinators and natural enemies of pests, and possible impact on crop yield, was studied for two mixtures (mixture A: <i>Borago officinalis</i>, <i>Coriandrum sativum</i>, <i>Glebionis coronaria</i>; mixture B: <i>Vicia sativa</i>, <i>Sinapis alba</i>, <i>Phacelia tanacetifolia</i>) in watermelon, cv. Karistan. The sown margins attracted primarily <i>Apis mellifera</i> and Halictidae bees (<i>Lasioglossum</i> spp.), and a few other Apidae (<i>Anthophora</i> sp., <i>Eucera</i> sp., <i>Bombus</i> sp.) over a flowering period of 6 weeks (beginning of April to mid-May). Pollinators on watermelon flowers were mainly Halictidae (<i>Lasioglossum</i> spp.) and fewer honey bees, from mid-May to mid-June. Shannon’s <i>(Η)</i> diversity index of parasitoids was higher in mixture B while their abundance did not differ between the plant mixtures, although it varied during the season. Higher weight/fruit, lower proportion of undeveloped/mature seeds per fruit, and higher Brix level in the field with the sown margins compared to a commercial watermelon, cv. Karistan, field, under common agronomic practices, suggest a positive effect of the sown margins on the crop yield.