FACTORS AFFECTING MORTALITY OF THE EUROPEAN CORN BORER, OSTRINIA NUBILALIS (HÜBNER), IN ALBERTA

Abstract

A combination of laboratory and field trials, from 1983 to 1985, were used to determine mortality factors affecting all life stages of Alberta populations of the European corn borer, Ostrinia nubilalis (Hübner), feeding on corn. The resulting life table demonstrated that greatest mortality occurred during the first and second larval instars (62.2%), when mature larvae are in diapause (69.5%), and from moth migration and loss in reproductive potential (70.3%). Stages where mortality was slight included the egg stage (11.7%), non-diapausing third- to fifth-instar larvae (2%), and pupae (10.4%).Laboratory trials showed that greater egg mortality occurred at relative humidities (RH) of 35 and 55% than at a RH of 75%. In the field, egg parasitism was nil, predation of early-instar larvae (5.2%) and diapausing larvae (6%) was low, and parasitoids were scarce (emerging from ca. 2% of pupae). Sustained periods of hot, dry weather with high moisture stress were related to mortality of both eggs and early-instar larvae. Death of early-instar larvae also was related to periods of rainy weather with low evaporation. The 64% non-diapause larval mortality was much lower than that reported elsewhere. The dramatic increase in the corn borer since its recent introduction to Alberta may be due to a lack of natural enemies, and because only non-resistant corn hybrids are grown.

Life Table Studies of European Corn Borer (Lepidoptera: Crambidae) with and without Inoculative Releases ofTrichogramma ostriniae(Hymenoptera: Trichogrammatidae)

“…In the absence of augmentative measures, natural mortality of O. nubilalis from egg to established larvae averaged 61% in sweet corn and 80% in Þeld corn in our study. These values are comparable to other studies of O. nubilalis ecology (Frye 1972, Lee 1988, Ross and Ostlie 1990. Inoculative releases of T. ostriniae increased total O. nubilalis mortality to 92% in sweet corn and 93% in Þeld corn.…”

“…A high percentage of O. nubilalis early instars failed to establish on corn (tunnel in stalk, ear, tassel, or leaf veins) based on the difference between the total number of eggs hatching and larvae sampled from plants. Primary factors contributing to this mortality include larval dispersal (Ross and Ostlie 1990), climate (Lee 1988), and predation (Frye 1972). In sweet corn, early-instar mortality averaged 81.3 Ϯ 3.5% in release plots and was lower (51.9 Ϯ 10.1%) in nonrelease plots (t ϭ 2.64, df ϭ 8, P Ͻ 0.01).…”

Natural parasitism of the European corn borer eggs Ostrinia nubilalis Hbn. (Lep., Pyralidae) by Trichogramma in Slovakia—need for field releases of the natural enemy

“…In 1959 in the warmest region of Slovakia. In 1980-1985 of the ECB eggs by Trichogramma evanescens was very low in southwestern Slovakia and at some locations it was not observed by B~ROVA in 1988.…”

Natural parasitism of the second generation European corn borer eggs Ostrinia nubilalis (Hübner) (Lepidoptera, Pyralidae) by Trichogramma spp. in sweet corn fields in Vojvodina, Serbia - short communication

“…Kania (1962Kania ( ) during 1956Kania ( -1959 field research in the vicinity of Wroclaw, Poland stated the same results. Similarly, no egg parasitism emerged from ECB egg masses field-collected in North America (Alberta) (Lee 1985). (Bírová 1988).…”