Cool Caterpillars: Low temperature biological control of a climbing cutworm

The growing season for many pests is during the summer where temperatures are often high; however, not all pests conform to this pattern. Abagrotis orbis is a climbing cutworm pest of vineyards in the Okanagan Valley. Eggs are laid and hatch in the fall and larvae overwinter as early instars. In the spring, the larvae begin to climb the grape vine and cause considerable damage by consuming the nascent buds. Thus the only windows for controlling this pest are in the fall and spring when temperatures are relatively cool.  The optimal development temperature for A. orbis is 15°C, and therefore it is important to find microbial control agents that operate effectively at this temperature. Here we screen a range of commercially available microbial control agents. We tested Metarhizium brunneum(F52), Beauvaria bassiana(GHA), Bacillus thuringiensis kurstaki(Dipel 2X), Heterohabditis megedis, Steinernema feltiae, and Steinernema kraussei in separate laboratory bioassays against A. orbis 1^st and 3^rd larvae at three temperatures: 10°C, 15°C, and 20°C. We found temperature and concentration effects, but no interactions. Both fungi achieved over 60% mortality at 10°C. Though not recommended for this organism, the nematodes were able to complete their lifecycle in A. orbis. H. megedis caused 50% mortality at 20°C, but at 10°C there was less than 15% mortality. S. kraussei  achieved over 60% mortality at 20°C and over 30% mortality at 10°C. The results indicate that either of the fungi will be suitable for field-testing, in addition to S. kraussei and S. feltiae either singly or in combination.