Vertical Distribution of Black Vine Weevil (Coleoptera: Curculionidae) Immatures and Infection by Entomogenous Nematodes in Soil Columns and Field Soil

Abstract

Vertical distribution of black vine weevil, Otiorhynchus sulcatus (F.), larvae and pupae, and depth of penetration of entomogenous nematodes on field-grown yews, Taxus cuspidate Siebold &Zuccarini, was studied. Black vine weevil larvae were found as deep as 30 cm, but the majority (>90%) were found in the top 15 cm. Distribution of pupae was similar to that of larvae. The distribution of infected black vine weevil immatures following an application of the nematodes Steinernema carpocapsae (Wieser) (All strain), S. feltiae (Filipjev), and Heterorhabditis bacteriophora (Poinar) (strains Cl and HP88) was studied in soil columns and field soils. Soil columns may not be effective models of nematode infection in undisturbed field soils. All species of nematodes tested were capable of moving to the bottom of 20-cm soil columns at a moisture content near field capacity to infect black vine weevil larvae. However, in the field, only S. carpocapsae infected larvae at that depth. S. feltiae infected larvae at depths of 17.5 cm, and H. bacteriophora (CI), which performed well in soil columns, did not infect larvae below 12.5 cm. In a laboratory bioassay, H. bacteriophora (CI) was 10 times more virulent (LC95 = 77 nematodes per cm2) than S. carpocapsae (LC95 = 794 nematodes per cm2). However, both species were equally effective in a field trial at the highest rate tested (2 × 105 nematodes per plant).