Pupation by Viburnum leaf beetle (coleoptera: chrysomelidae): behavioral description and impact of environmental variables and entomopathogenic nematodes

Pyrrhalta viburni (Paykull), a new landscape pest in the United States, feeds in both the larval and adult stages on foliage of plants in the genus Viburnum. The insect is univoltine, with larvae active in spring and adults throughout the summer months. Experiments were conducted to determine the depth of pupation in the soil; the impact of substrate texture, moisture content, and temperature on pupation success; and ability of entomopathogenic nematodes to kill larvae when they enter the substrate to pupate. Larvae burrowed only a short distance into the substrate when pupating; 97-100% were found within the top 3 cm of a column of soil or sand and soil mixture in the laboratory. Larval mortality before pupation was low at 22 degrees C but considerably higher at 30 degrees C; at both temperatures, pupation success was lowest on a mixed substrate and higher (and equivalent) on sand or soil alone. Survivorship to adult was influenced by both temperature and substrate moisture content; at 22 degrees C, 56% percent of pupating larvae emerged as adults at 75% moisture content compared with only 25 at 25% moisture content. Emergence of adults was negligible at 30 degrees C, regardless of moisture content. Heterorhabditis bacteriophora and Steinernema carpocapsae were very effective biocontrol agents in laboratory bioassays, reducing adult emergence by 76-100%, with nematode applications made before pupation being more effective than those made after pupation, and H. bacteriophora consistently (but not significantly) more effective than S. carpocapsae. Management methods that take advantage of pupation behaviors are discussed.