Phenology of the Adult Spotted Cutworm 1 in the Yakima Valley

Abstract

In Washington, there were 2 flights of adult spotted cutworm, Amathes c-nigrum (L.), yearly and 2 generations of larvae; the 2nd-generation larvae overwintered and completed development in the spring. A partial, small 3rd flight appeared occasionally. The sex ratio of laboratory-reared specimens was 1♂:1♀. Blacklight (BL) traps caught as many as or more females than males 16% of the time, which indicated that both sexes were attracted equally, but 84% of the time BL traps caught 15–20% more males than females because of the abundance and behavioral differences of males. The sex ratio became skewed in favor of males in the 2nd flight; females diminished to as little as 5–10% of the catch in Sept. and Oct. The female spotted cutworm proved to be polygamous, and some mated as many as 9 times. The average number of matings was 2 for 1st flight and 3 for 2nd flight females. There were seasonal increases in mating frequency in each flight. Most mated females that were trapped were in a reproductive condition. Populations were observed to grow and decline in response to environmental factors and not necessarily as a reflection of the size of the preceding population. The specific environmental factors that cause such fluctuations have not been isolated.