When Do Annual Bluegrass Weevils Emerge in the Spring?
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.
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
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
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
- 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
- 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.|
Determining the Reproductive Phenology of Emerging Overwintering
Annual Bluegrass Weevil Populations for the Optimization of Management Programs