European corn borer and its parasites overwintering abundance and damages on different corn FAO maturity groups

Abstract

European corn borer (ECB) is one of the most significant maize pests in the world and also in Croatia. ECB causes yield reduction from 2 to 25%, even more in years favorable for its development. According to estimations, these losses are around 7%. About 90% of the hybrids had some resistance to whorl-leaf feeding (first-generation ECB) and 75% had some resistance to sheath and sheath-collar feeding (secondgeneration ECB). Along with resistance, modern maize hybrids possess certain level of tolerance. The main aim of this paper was to determine moth eclosion of the overwintering generation and presence of the parasites of ECB larvae during the overwintering as well as to estimate population density of ECB on maize growing area in Croatia. Also, the aim was to establish the differences among maize FAO maturity groups in damage caused by ECB larvae. Estimated overwintering population was over 8,000 moths/ha i.e. more than 4 million larvae of first generation. During the overwintering four different parasites attacked the larvae. Two species belong to the order Hymenoptera (Cotesia marginiventris Cresson and Eriborus terebrans Gravenhorst) and two species belong to the order Diptera (Ramonda spathulata Fallén and Lydella thompsoni Herting). One caterpillar predator species Paragymnomerus spiricornis Spinola (Hymenopetra) overwinters in maize stalks as well. The highest attack of the first ECB generation was recorded on FAO maturity group 500. The damage from second ECB generation was the highest on FAO groups 400 and 500. The maize of the higher FAO groups has high and robust stems with large number of big leaves. That intensive vegetative growth is a biological characteristic that attracts first generation of ECB to intensifying egg lying. High population level of the first generation may lead to high level of second ECB Original scientific paper

Weather Conditions and Maturity Group Impacts on the Infestation of First Generation European Corn Borers in Maize Hybrids in Croatia

“…For example, Patch [ 35 ] reported that the height of maize or a factor, such as maturity correlated with height, was the main factor in the selection of maize by the ECB moths for oviposition. Maize hybrids planted earlier and the hybrids with extensive vegetative growth were attractive to moths to lay eggs, and therefore those hybrids suffered higher infestation from first generation ECB [ 25 , 32 ]. Recent investigations conducted by Leppik and Frérot [ 36 ] reported on maize odorscapes under field conditions that may improve host plant detection in ECB moths during oviposition.…”

“…The results with Croatian hybrids and their tolerance to ECB reported by Ivezić and Raspudić [ 15 ], Lemić et al [ 25 ] and Augustinović et al [ 33 ] were based either on smaller number of hybrids or on the few locations included in the investigation. The lack of correlation between the FAO maturity group and the percent of infestation obtained in our study was in line with the data reported by Augustinović et al [ 33 ], who reported significant differences in the intensity of the damaging effects on different locations and no significant differences concerning various hybrids.…”

“…Overwintering success together with climatic conditions are the key factors determining the abundance and intensity of the attack of the first generation [ 25 ]. Lemić et al [ 25 ], in their research, estimated that 8000 moths/ha can overwinter if a corn field is left unploughed. If one female moth can lay approximately 500 eggs [ 26 ] that results in 4 million larvae of the first generation.…”

“…This is a biological characteristic that attracts the first generation of ECB, and thus, they lay more eggs. A high population level of the first generation could lead to a high level of second ECB generation, which can cause a yield reduction in the hybrids with longer vegetation periods (medium-late FAO maturity groups) [ 25 ].…”

“…FAO maturity groups may differ in their sensitivity to the first generation of ECB [ 25 , 33 ]. However, the sensitivity is also correlated with weather conditions, in particular with the average daily temperatures, relative air humidity, and the total amount of rainfall in May and June when egg laying and hatching and larval development is expected.…”