2007 Season Review: Agronomic Insects

Larry Bledsoe, Department of Entomology, Purdue University

Primary crop pests in 2007 were corn rootworm and soybean aphid. Second stage western corn rootworm, Diabrotica virgifera, (WCR) larvae were first detected in Tippecanoe County in corn roots on 23 May. First stage larvae were likely present by 18 May. This emergence estimate was about 10 days earlier than observed in 2006 and was probably related to the warm spring temperatures. WCR adults were first detected in emergence traps in northwest Indiana in late June. WCR adult abundance was average. The variant WCR was still a primary concern in counties north of Indianapolis. The incidence of first and second-generation European corn borer, Ostrinia nubilalis, (ECB) infestations followed the pattern of decline observed for several years. The pervasive use of ECB-resistant corn hybrids has markedly diminished the pest status of this insect.

Soybean aphid, Aphis glycines, (SBA) abundance in the fall of 2006 was abnormally high which suggested a potential outbreak in 2007. The host plant, Rhamnus cathartica and SBA broke dormancy during the abnormal warm March temperatures. This was followed by extreme cold in early April. SBA surveys conducted before and after the aberrant weather suggested that the SBA population in northern Indiana had diminished greatly from the levels detected in the previous fall. The abnormally hot late summer temperatures were associated with reduced SBA fecundity and/or increased mortality. Natural control agents may also be adjusting to the presence of SBA and contributing to the stabilization of regional populations. Very few localized SBA outbreaks occurred requiring pesticide application. Japanese beetle, Popillia japonica, adult and larval injury to field crops was very localized and the overall impact was minimal.

Corn earworm, Helicoverpa zea, adults were present in high numbers late in the season, however, only trivial injury to field corn was reported. Alfalfa weevil, Hypera postica, injury to alfalfa was moderated by the below freezing temperatures that occurred in early April and never recovered to significant pest status.

Potato leafhopper, Emposaca fabae, injury tended to be severe at midsummer in areas where droughty conditions reduced alfalfa growth and recovery. Several new crop pests reached levels in Indiana in 2007 that warranted greater consideration. The western bean cutworm, Striacosta albicosta, became more prominent in field corn in several north-central and northwestern counties. The level of infestation of corn ears was reported to range from trivial to a few reports of about 25% in localized areas of fields. Asiatic garden beetle, Maladera castanea, larvae were found to be damaging corn roots in very localized areas within fields with sandy soils in several northeast counties.