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Individual study: Effects of tillage and irrigation practices on wild bees on pumpkin farms in northern Virginia and Maryland, USA

Published source details

Julier H.E. & Roulston T. H. (2009) Wild bee abundance and pollination service in cultivated pumpkins: farm management, nesting behaviour and landscape effects. Journal of Economic Entomology, 102, 563-573


Tillage (ploughing/cultivation) and irrigation may affect ground-nesting bee species, such as the common Eastern bumblebee Bombus impatiens and the squash bee Peponapis pruinosa (which collects pollen only from the family Cucurbitaceae, including pumpkins Cucurbita pepo). This study examined the effects of no-tillage and irrigation on wild bee abundance on pumpkin farms in northern Virginia and Maryland, eastern USA.

Twenty farms were selected, each with at least 0.4 ha of pumpkin, grown for at least one year before the study. Ten farms had tilled the previous year’s pumpkin patch to an average depth of 25 (± 5.5 cm) cm in autumn or spring. Nine of these had also tilled a new pumpkin patch, usually in a different location. These were paired with 10 farms (2.3 – 17.6 km away) with similar histories of pumpkin cultivation and similar levels of insecticide use but which had not tilled the previous year’s pumpkin patch, leaving it undisturbed or planting a no-tillage crop.
Bees visiting pumpkin flowers were identified and counted between 8:00 and 10:00 h in mid-July and again in August 2006, on five 50 m transects of pumpkin field at each study farm.
Six farms were irrigated, five with overhead irrigation, one with drip irrigation.

There was no significant difference in the number of squash bees or bumblebees between farms that tilled after the pumpkin crop and those that did not. However, the pumpkin crop flowers later than other cucurbits and the authors suggest a tillage effect on squash beesmay have been masked by bees dispersing early in the season to find forage elsewhere.

Irrigation increased the number of bees, perhaps by making the soil softer. Irrigated farms had significantly more squash bees than paired non-irrigated farms (average of 27.2 bees recorded at irrigated farms and 9.0 bees at non-irrigated farms).

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