**3. The role of plant defense mechanisms against herbivory**

Plants have developed direct and indirect defense mechanisms against herbivores. Direct plant defense is reflected through primary and secondary metabolites (silica, trichomes, proteinase inhibitors, polyphenol oxidases, toxic compounds, and other). The indirect defense is plants' ability to attract insect predators by emitting different volatile organic compounds [21]. Blend structure of volatiles is specific and very complex and depends on plant and herbivore species, plant developmental stage, and environmental conditions [22]. Many plants induce volatile emissions only during the photo phase, while many lepidopteran larvae are nocturnal insects and consume plant material during the night. Damaged plants may emit volatiles for the attraction of natural enemies. Adult insects may avoid these plants for egg deposition; however, lepidopteran larvae could be attracted to induced volatiles [23]. To reveal and better understand signaling pathways between plants and insects, plant defense mechanisms post herbivory attack have been in the focus of many researchers, so far. In a study of the Asian Corn Borer (*Ostrinia furnacalis*), it is found that females laid fewer eggs on damaged plants by insect larvae than mechanically damaged or healthy plants [24]. The blends of plant volatiles are tested to attract gravid females and manipulate with a population of pests as well [25]. The ECB is considered a model insect for studying the sex pheromone communication system [26, 27]. Several strains of ECB (E, Z, and E/Z) are recognized in the world [28], while in eastern Croatia Z-strain is present only [29].

## **4. The role of nitrogen and C/N ratio on the intensity of the ECB attack**

A high amount of nitrogen in the soil system is unavailable for plants. Nitrogen fertilization is applied according to the plans of plant nutrition and expected yields. Nitrogen also rinses in groundwater, so it is necessary to ensure plants with a sufficient amount of nitrogen fertilizer. Plant dry matter contains

**81**

**Table 1.**

*The Role of Irrigation and Nitrogen Fertilization on the Feeding Behavior of European Corn Borer*

2–5% of nitrogen. In soils with higher pH, plants prefer ammonium form of

The quality of host plants influences the feeding behavior of insects. Plant nitrogen and carbon concentrations as well as other metabolites directly affect insect fertility (oviposition, size, and quality of egg masses). The quality of the host plant is being changed due to damage caused by insect feeding [30]. Plants in treatments with nitrogen fertilization have been damaged more intensively from lepidopteran larvae than plants without fertilization. The plants with the highest growth potential attract lepidopteran pests. This attractive behavior of pests is mostly affected by the plants' nitrogen concentration [31]. High nitrogen supply usually increases protein production and decreases carbohydrates, so plants have softer tissue, and they are more susceptible to the ECB attack [32]. Contradictory results are reported on the effect of sulfur and calcium concentration in maize leaves concerning plant defense mechanisms. The consensus has been made, and their interaction is very important in plant protection against herbivores [33]. Mixtures of lignin, proteins, minerals, and carbohydrates are organic compounds that contain a different ratio of carbon and nitrogen, which is usually abbreviated to the C/N ratio. Preferably, ECB attacks plants that contain higher nitrogen concentration and a narrower C/N ratio. The susceptible plants, those with the highest damages, are characterized by high lignin content and decreased C/N ratio [34]. We aimed to evaluate the role of irrigation and nitrogen fertilization on the

The open field experiment was set up at the Agricultural Institute Osijek, Croatia (45° 33′27.11N, 18°40′46.52E) during three vegetation seasons: 2012, 2013, and 2014. We tested the efficacy of three treatments of irrigation and nitrogen fertilization on ECB attack on four different maize genotypes. Soybean was used in crop rotation. A factorial experimental design, the split-split plot, was used with three replications. Each independent variable was one factor in experimental design. Three levels of irrigation and nitrogen fertilization are applied for each

**Factor A B C**

(control)

A2—60–100% FWC

A3—80–100% FWC

**Irrigation Nitrogen fertilization Hybrid**

B1—soil nitrogen (control) C1—OSSK 596

B2—100 kg N ha<sup>−</sup><sup>1</sup> C3—OSSK 602

B3—200 kg N ha<sup>−</sup><sup>1</sup> C3—OSSK 552

C2—OSSK 613

The area of the experimental field was 0.5 ha. The basic plot consisted of two maize rows 10 m long. Row spacing was 70 cm. The first three rows at the edges of fertilization plots were omitted in evaluations. Maize was sown with hand planters

with two seeds per together and thinned in the phase of 4–6 leaves plants.

*DOI: http://dx.doi.org/10.5772/intechopen.92598*

ECB attack on maize in Croatia.

tested maize genotype 3 × 3 × 4 (**Table 1**).

Treatment A1—natural rainfall

**5. Experimental design**

*FWC, field water capacity.*

*Factors and treatments in the experiment.*

nitrogen, and in soils with lower pH, nitrate form.

*The Role of Irrigation and Nitrogen Fertilization on the Feeding Behavior of European Corn Borer DOI: http://dx.doi.org/10.5772/intechopen.92598*

2–5% of nitrogen. In soils with higher pH, plants prefer ammonium form of nitrogen, and in soils with lower pH, nitrate form.

The quality of host plants influences the feeding behavior of insects. Plant nitrogen and carbon concentrations as well as other metabolites directly affect insect fertility (oviposition, size, and quality of egg masses). The quality of the host plant is being changed due to damage caused by insect feeding [30]. Plants in treatments with nitrogen fertilization have been damaged more intensively from lepidopteran larvae than plants without fertilization. The plants with the highest growth potential attract lepidopteran pests. This attractive behavior of pests is mostly affected by the plants' nitrogen concentration [31]. High nitrogen supply usually increases protein production and decreases carbohydrates, so plants have softer tissue, and they are more susceptible to the ECB attack [32]. Contradictory results are reported on the effect of sulfur and calcium concentration in maize leaves concerning plant defense mechanisms. The consensus has been made, and their interaction is very important in plant protection against herbivores [33]. Mixtures of lignin, proteins, minerals, and carbohydrates are organic compounds that contain a different ratio of carbon and nitrogen, which is usually abbreviated to the C/N ratio. Preferably, ECB attacks plants that contain higher nitrogen concentration and a narrower C/N ratio. The susceptible plants, those with the highest damages, are characterized by high lignin content and decreased C/N ratio [34]. We aimed to evaluate the role of irrigation and nitrogen fertilization on the ECB attack on maize in Croatia.

### **5. Experimental design**

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

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].

Plants have developed direct and indirect defense mechanisms against herbivores. Direct plant defense is reflected through primary and secondary metabolites (silica, trichomes, proteinase inhibitors, polyphenol oxidases, toxic compounds, and other). The indirect defense is plants' ability to attract insect predators by emitting different volatile organic compounds [21]. Blend structure of volatiles is specific and very complex and depends on plant and herbivore species, plant developmental stage, and environmental conditions [22]. Many plants induce volatile emissions only during the photo phase, while many lepidopteran larvae are nocturnal insects and consume plant material during the night. Damaged plants may emit volatiles for the attraction of natural enemies. Adult insects may avoid these plants for egg deposition; however, lepidopteran larvae could be attracted to induced volatiles [23]. To reveal and better understand signaling pathways between plants and insects, plant defense mechanisms post herbivory attack have been in the focus of many researchers, so far. In a study of the Asian Corn Borer (*Ostrinia furnacalis*), it is found that females laid fewer eggs on damaged plants by insect larvae than mechanically damaged or healthy plants [24]. The blends of plant volatiles are tested to attract gravid females and manipulate with a population of pests as well [25]. The ECB is considered a model insect for studying the sex pheromone communication system [26, 27]. Several strains of ECB (E, Z, and E/Z) are recognized in the world [28], while in eastern Croatia

**4. The role of nitrogen and C/N ratio on the intensity of the ECB attack**

A high amount of nitrogen in the soil system is unavailable for plants. Nitrogen fertilization is applied according to the plans of plant nutrition and expected yields. Nitrogen also rinses in groundwater, so it is necessary to ensure plants with a sufficient amount of nitrogen fertilizer. Plant dry matter contains

**3. The role of plant defense mechanisms against herbivory**

**80**

**Figure 3.**

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

Z-strain is present only [29].

The open field experiment was set up at the Agricultural Institute Osijek, Croatia (45° 33′27.11N, 18°40′46.52E) during three vegetation seasons: 2012, 2013, and 2014. We tested the efficacy of three treatments of irrigation and nitrogen fertilization on ECB attack on four different maize genotypes. Soybean was used in crop rotation. A factorial experimental design, the split-split plot, was used with three replications. Each independent variable was one factor in experimental design. Three levels of irrigation and nitrogen fertilization are applied for each tested maize genotype 3 × 3 × 4 (**Table 1**).


#### **Table 1.**

*Factors and treatments in the experiment.*

The area of the experimental field was 0.5 ha. The basic plot consisted of two maize rows 10 m long. Row spacing was 70 cm. The first three rows at the edges of fertilization plots were omitted in evaluations. Maize was sown with hand planters with two seeds per together and thinned in the phase of 4–6 leaves plants.

