When Do Annual Bluegrass Weevils Emerge In Spring March 11, 2015

Annual bluegrass weevil eggs are generally three different colors. For 15 weeks, females are capable of laying up to 3 eggs per day, for a maximum of 130 eggs.

The annual bluegrass weevil, Listronotus maculicollis, is the most destructive insect pest of golf course turf in the northeastern United States and Canada. Despite this weevil’s expanding range, there is a fundamental lack of understanding of its life cycle, which leads to increased insecticide usage. With USGA funding, researchers at the State University of New York - Delhi, and University of Massachusetts – Amherst, investigated the reproductive development of emerging weevil populations, determined when feeding and mating occur, and when adults cease to lay eggs.

For two years, the researchers made weekly collections of adult weevils by vacuuming greens, tees, and collars on a golf course in upstate New York. The sampling period began prior to when Forsythia blooms, a traditional indicator used to estimate adult emergence from overwintering sites. Adults were dissected to examine reproductive maturity, feeding, and whether mating occurred. Degree-days, calculated on a daily basis by on-site weather stations using base temperature 50°F, measured heat accumulation required for insect development

Adult emergence by calendar date was substantially different between 2012 and 2013 (March 18 and April 30, respectively), though degree-day accumulation ranges were similar. The scientists observed two peaks in adult density in each year. The first, and most dense peak, occurred at similar temperature ranges (122 and 139 degree-days) despite differing by approximately 3 weeks. Other important findings include:

  • Female weevils arrive on short mown playing surfaces with mature reproductive systems, whereas the majority of males are largely immature and incapable of fertilizing eggs.
  • In both years of the study, only a low percentage of adults fed prior to reaching the short mown turf areas. Adult feeding rapidly increased after the peak in adult density on playing surfaces.
  • Females require multiple matings to continue laying eggs over several weeks to months.
  • Females are capable of laying up to 3 eggs per day, for a maximum of 130 eggs. Egg laying occurred over a 15 week period in both years of the study, with strong correlations to degree-day accumulations for the first 5 weeks (See Figure 1). 

The graph illustrates the relationship between average number of eggs laid per female per week (gray bars) and the degree-days (base 50°F) accumulated during the week (line with circles) in caged egg laying studies during 2012 and 2013.