How long does it take for corn rootworm eggs to hatch?
Western corn rootworm (WCR) and northern corn rootworm (NCR) eggs overwinter in the soil and larval hatch is based on accumulated degree days (ADD) of soil temperatures each year. Average hatching dates for Iowa are in early June, with southern counties experiencing egg hatch before northern counties. Soil texture, snow cover or residue, and depth of egg placement will all effect the ADD of corn rootworm eggs and subsequent egg hatch. Peak egg hatch (or 50%) of corn rootworm happens between 684-767 soil ADD (base 52ºF); expect to see adults emerge 7-10 days after reaching the peak.
How long will adult corn rootworm adults emerge?
The corn rootworm adult emergence period (time between the first and last adult) is lengthy compared to other corn pests. This is due, in part, to highly variable ADD that happens with soil-dwelling insects. Normally the emergence period is about six weeks, but can be extended to eight or more weeks depending on summer temperatures. The summers of 2014 and 2015 are good examples of new adults emerging later in the summer. To estimate how long adult emergence will last, we must determine the biofix (or significant capture). The biofix for corn rootworm is when the first adult detected each year. After the biofix is set, we use ADD with air temperatures and baseline developmental temperatures to estimate important benchmarks. The upper developmental threshold is 95ºF and the lower developmental threshold is 53ºF. Benchmarks for western and north corn rootworms include:
* WCR Males: 50% (118 ADD), 90% (278 ADD), 100% (505 ADD)
* WCR Females: 50% (245 ADD), 90% (429 ADD), 100% (629 ADD)
* NCR Males: 50% (169 ADD), 90% (348 ADD), 100% (570 ADD)
* NCR Females: 50% (268 ADD), 90% (449 ADD), 100% (643 ADD)
In short, WCR develop faster than NCR; males develop faster than females.