Effect of Soil Type on Carrot Weevil Movement Behavior

To examine the effect of soil type on carrot weevil, Listronotus oregonensis, (Coleoptera: Curculionidae), movement behavior we conducted a series of laboratory arena experiments with the use of three soil types: mineral soil, organic soil and pure sand. We found that soil type influences carrot weevil burrowing activity and movement and showed that carrot weevil is more inclined to burrow into mineral and organic soils than pure sand and displays avoidance of the latter. While barriers constructed out of pure sand induced burrowing activity only in 3% of tested weevils, mineral and organic soil barriers initiated burrowing in 67% and 38% of tested weevils respectively. All weevils crossed pure sand barriers, whereas 18% (mineral soil) and 6% (organic soil) were arrested and engaged in burrowing activities. In addition, carrot weevil movement behavior at the border of two substrates, revealed high edge permeability of mineral and organic soils and reduced permeability of pure sand edges. Over 70% of weevils released on organic soil ended up not crossing the border with another substrate. All tested weevils released on pure sand crossed the border within less than 1 min. Replication of the experiments with autoclaved soil suggested that the observed differences in carrot weevil movement behavior were largely due to soil texture and not strongly influenced by micro-organisms or odor.