Measuring and modelling the dispersal of Coccinella septempunctata (Coleoptera: Coccinellidae) in alfalfa fields

Abstract

Dispersal of the sevenspotted lady beetle, Coccinella septempunctata, was measured in a series of mark-release-recapture experiments in Utah alfalfa. In three experiments, samples were taken in a radial pattern around the release point. Released beales for the most part left the 0.36 ha (68 m diameter) sample area within 24 hours, and their average residence time in the sample area was calculated as 12, 6 and 1.6 h in the three experiments, respectively. The spatial distribution of beetles around the point of release could be described with normal distributions whose variance increased linearly in time with 3.8. 1.1 and 0.34 m2 per hour. In three additional field experiments the departure of marked beetles was compared between sugar-sprayed plots and control plots. Residence time was 20-30% longer in sugar-sprayed plots than in control plots, with mean residences of 5.3, 3.6, and 2.9 h in the sugar-sprayed plots in the three experiments, respectively, and means of 4.4, 2.7, and 2.4 h in the control plots. The density of unmarked beales rose by a factor of 10-20 in the sugar sprayed plots during the first 4 to 6 hours following early morning spraying of sugar. This rapid and substantial increase in density cannot be explained by the slightly longer residence time in sugar-sprayed plots. We hypothesize that the aggregation in sugar-sprayed plots is mostly due to greatly increased immigration into those plots, in response to volatiles produced by the plant-pest-predator assembly.