Predicting emergence in a Midwestern population of Cotinis nitida (Coleoptera: Scarabaeidae): An update

The Green June beetle, Cotinis nitida (L.), is an important pest of grapes, peaches, blackberries, blueberries, apples, and pears that is native to North America. The control measures (sprays or cultural control) require á priori planning and proper timing of operations.

To that end, the number of cumulative degree days (CDDs) that this species requires for outbreak have recently been delineated in our preliminary research between 2009 and 2013 using traps baited with isopropanol. To verify the validity of our CDD calculations for 2009–2013, we extended the period of green June beetle monitoring by 7 consecutive years (2014–2020) in the same location, using the same methods.

The mean (±SE) number of CDDs at the first flight calculated for 2009–2013 equaled 888.96 ± 36.78, and that recorded for 2014–2020 reached 867.17 ± 11.23. No significant differences were found (t = 0.6543, df = 10, P = 0.5277). Similarly, there were no differences between mean numbers of CDDs at the peak of green June beetle population density. From 2009–2013 the number of CDDs equaled 1,237.68 ± 25.31, whereas in 2014–2020 it reached 1,259.17 ± 36.68. Again, no significant differences were found (t = 0.4408, df = 10, P = 0.6687). CDDs averaged across all 12 years of the monitoring period (2009–2020) equaled 876.25 ± 15.99 for first catch and 1,250.22 ± 23.14 for the peak.

Our findings presented herein validate the method of predicting Green June beetle outbreaks proposed previously by our team.