Enhanced Biological Control of the Cereal Leaf Beetle

Many biological and environmental interactions can affect the biological control of the cereal leaf beetle (CLB; Oulema melanopus [L.]). We studied the biological control potential of predatory lady beetles and a parasitoid wasp in fall wheat (Triticum aestivum L.). Lady beetles were surveyed in grain fields with high CLB density (up to 50 CLB larvae per 0.09m2). The effects of sugar applied to wheat as an additional food source for Tetrastichus julis (Walker) were also measured. The CLB population followed the typical pattern of high adult and egg numbers in May, peak larval numbers in late May, and a decline throughout June. High lady beetle numbers (0.06-0.34 per m2, versus 0-0.04 per m2 in control plots) in sugar spray plots resulted in a small decrease (14%) in CLB larval numbers from 23 May to 5 June, 2006. Lady beetles had no impact on CLB densities after 5 June. Two lady beetles, Coccinella septempunctata L. and Hippodamia convergens Guerin, were unable to reproduce for more than three days after being placed on an exclusive CLB larvae diet, suggesting CLB is not a suitable food source. Other lady beetles placed on an exclusive aphid diet, which is a preferred food source, laid eggs for 15 days. Parasitism rates of CLB larvae by T. julis were also tracked, and low rates early in the season (8-30%) developed into high rates later in the season (75-78%). In early June, CLB parasitism in sugar spray plots (26.8%) was higher than parasitism in control plots (8.9%). Later in June, there was no significant difference between treatments. Laboratory results demonstrated an increased longevity of T. julis as a result of accessible sugar in the diet. Overall, results suggest that providing an additional nutrient source at select times of the season where T. julis is established could reduce CLB populations. Thereafter, predation by lady beetles might contribute to suppressing CLB.