Estimating Corn Rootworm Beetle Populations with Sticky Traps

Objectives

Quantifying corn rootworm beetle populations in the summer allows growers to make better informed decisions regarding management options the following season.
A survey was conducted in 2016 to estimate corn rootworm population levels in fields throughout the central and northern Corn Belt using Pherocon® AM/NB sticky traps.

Study Description

Year: 2016
Locations: 773 fields in Iowa, Illinois, Minnesota, Nebraska, and South Dakota
Sampling Methods:
- Sticky traps placed in field beginning at blister stage (R2)
- Sticky traps placed per field: 1 or 6
- Beetles counted on each trap at 7-day intervals with the average per trap recorded
- Trapping continued for 4 to 6 consecutive weeks
- Trapping was conducted in both continuous corn and corn soybean rotated fields

Results

Corn rootworm population levels were categorized at zero, low, moderate, or high for each sampling location in 2016:
- Zero = no beetles collected
- Low = traps average < 21 beetles/week
- Moderate = traps average 21-50 beetles/week
- High = traps average >50 beetles/week
Maximum corn rootworm beetle population levels observed by location across all weeks (Figure 1 and Figure 2):
- 8.4% of locations had high populations
- 10.9% of locations had moderate populations
- 75.8% of locations had low populations
- 4.9% of locations had zero adults collected
Previous crop appeared to influence beetle populations. Across all locations the average maximum count for corn after corn was 21.6; whereas, corn after soybean was 7.6 (Table 1 and Figure 3):

Table 1. Effect of previous crop on maximum beetle count averaged across all locations.

Previous Crop	Average Beetle Count	Locs
Corn	21.6	408
Soybeans	7.6	305

Action Thresholds

Management Considerations

Although Pioneer studies have shown that the HXRW trait remains an effective tool for corn rootworm management, Pioneer and university research suggests that continuous, uninterrupted use of the same corn rootworm Bt technology can lead to decreased corn rootworm susceptibility to that technology, and may result in reduced product efficacy against these insects.
To help maintain the efficacy of Bt corn rootworm products, it is essential to develop a multi-faceted rootworm management plan.
Your Pioneer Sales Professional or local Extension professionals can assist you in developing best management practices for your operation
Please contact your authorized Pioneer Representative or consult with your local University Extension for more information regarding insect resistance management, best management practices and to understand whether there has been insect resistance documented in your area.