**2.2 Potential of ECB natural enemies**

During the vegetation, ECB has been exposed to different species of natural enemies, such as wasps and flies that feed on eggs or larval stages of this pest. The most investigated natural enemies of ECB are *Trichogramma* spp*.* Contradicting results on their effectiveness have been reported [18]. *Trichogramma* wasps are insect egg parasitoids. We have detected the natural parasitism of ECB eggs by these wasps in Croatia on the second generation of ECB. We reported low populations of natural enemies in the field crop, insufficient to significantly reduce the population of ECB and keep it under the economic threshold. Only artificial release of

**Figure 2.** *Leaf damage from ECB larvae (Photo: Sarajlić, 2010).*

*Pests, Weeds and Diseases in Agricultural Crop and Animal Husbandry Production*

tool in integrated pest management programs against ECB. Plant breeders successfully developed hybrids with stronger stalk, a larger root system, and such plants are more tolerant to this pest. Tolerant hybrids are also characterized by the low potential of plant lodging and yield losses in conditions of the highest ECB infestation and stalk damage [3, 4]. One ECB larvae per plant on commercial hybrids can reduce yield up to 6.05% [5]. The amount of plant-available water has been studied as a potentially important factor for ECB infestation and damage. Irrigated plants have a higher yield, and grain quality is better [6]. If the water supply is satisfactory, plants will adsorb more micro and macro elements. Nitrogen is the most important essential element, and plants adsorb it in a mineral form. Agricultural soils usually contain 0.1–0.3% of nitrogen, and from this, only 1–3% is available for plants. Maize plants under nitrogen fertilization treatment are attractive for ECB females for laying eggs. Such plants contain more quality ingredients for larval nutrition. The positive correlation between nitrogen fertilization and ECB oviposition and larval feeding was found by many researchers [7–9]. C/N ratio is important for immobility and mineralization processes and varies with levels of nitrogen fertilization. If the C/N ratio is wider than 1:25, nitrogen would become immobile. However, if the ratio is narrower, the mineralization is possible. Plants alone are complex systems in which a lot of factors interact; therefore, we should elucidate damage potential of ECB in changing environments and techniques that will enable better and sustainable protection of

European corn borer (*Ostrinia nubilalis* Hübner) (Crambidae, Lepidoptera) (**Figure 1**) is a destructive pest on maize, but it also occurs on many other plant species such as peppers and tomatoes. In eastern Croatia, ECBs have been studied for many years [10, 11], population dynamics and intensity of attack of ECB have been monitored since 1965 (Ivezić, personal commun.). In Croatia, ECB usually develops two generations per year; however, the third generation may occur in years with favorable agro-climatic conditions [12]. Larvae feed on aboveground parts of a plant and pass through five larval stages before attaining the pupal stage. The first larval stage tends to move toward higher moisture conditions in

**78**

**Figure 1.**

*Female and male of European corn borer (Photo: Sarajlić, 2010).*

plants against this pest.

**2. European corn borer**

#### **Figure 3.** *ECB pupae inside maize stalk (Photo: Sarajlić, 2010).*

these wasps may be considered as a reliable suppressant of ECB [19]. *Trichogramma* spp*.* has a great potential in biological control of sweet maize, where ECB has been controlled by chemicals that pose an environmental and toxicological threat [20].
