**3. Results**

It has been verified that of the 866 Bt maize plants evaluated in the vegetative physiological stage V6, 699 (80.7%) of the plants were attacked by the *D. melacanthus* stinkbug. The maize leaves presented evident damage by the presence of punctures or holes produced by the feeding of bed bugs with an average number of 6.1 punctures per plant. On the other hand, 167 maize plants (19.9%) were not attacked or did not present the characteristic symptoms described for *D. melacanthus* (**Table 1**).

The average number of *D. melacanthus* plants attacked was 87.4 ± 7.8 and 20.8 ± 2.79 not attacked, from an average population of 108.2 plants, considering the eight Bt maize areas evaluated in which there were between 100 and 117 plants.

The high value of maize plants attacked is due to the fact that the Cry protein, expressed by the Bt event, the seed treatment and the foliar application with neurotoxic insecticides were unable to provide protection to the maize plant from the


#### **Table 1.**

*Number of Bt maize plants and height of plants (cm) attacked by* D. melacanthus *and not attacked.*

*Productive and Economic Losses Caused by* Dichelops melacanthus *in Transgenic Bt Maize… DOI: http://dx.doi.org/10.5772/intechopen.112390*

attacks of *D. melacanthus*. On the one hand, the protein crystals of *B. thuringiensis* are non-toxic to pentatomidae bugs and on the other hand, the insecticide imidacloprid applied *via* seed and foliar was inefficient in controlling the population of pest hemipterans.

In relation to the variable height of the Bt maize plants, attacked or not by *D. melacanthus*, no statistically significant difference (p > 0.05) was verified between the populations. An average height of 41.5 cm was recorded for unattacked plants and an average height of 41.2 cm for attacked plants (**Table 1**).

These results reveal that the height growth of maize plants is not affected, however, the leaf area is compromised by the feeding punctures of the stink bugs, which in turn affect the photosynthetic capacity of the plant and the translocation of photoassimilates to the drainage region for the formation of corn kernels, which reduces their weight.

It has been verified that the average weight of grains per Bt maize plant not attacked by *D. melacanthus* was 3956 ± 269 g and for the attacked plants it was 3048 ± 199 g with significant statistical differences between them (p < 0.05). It has also been estimated that the average yield per hectare of the unattacked Bt maize plants was 2197.77 kg/ha and those attacked, 1693.33 kg/ha, thus the loss in maize production was 504.44 kg /ha due to damage caused by *D. melacanthus*. In this sense, considering the average value of corn in the corresponding harvest, the loss of income was 98.93 dollars per hectare (**Figure 1**).

### **4. Discussion**

According to the data referring to plants attacked and not, a high incidence of the green-belly bug has been verified in the Bt maize crop itself with applications of Imidacloprid insecticides (200 ml/ha). Probably the high occurrence of *D. melacanthus* is due to the resistance to the active principles applied during the development of

#### **Figure 1.**

*Average kernel weight ± SD (g) per Bt maize plant not attacked and attacked by* Dichelops melacanthus*. Average values followed by different letters differ from each other by Student's T-test at 5% significance.*

maize. Another aggravating factor is that soybeans grown before corn also host a large number of bugs and the same chemicals are used to control them, which generates selection pressure for resistant biotypes.

No significant differences were observed in the height decrease of attacked and unattacked maize plants. This is compatible with those obtained by Crosariol Netto et al. [12], who observed that the transgenic plants did not show significant differences in relation to the height and respond differently to conventional non-Bt hybrids than if they can reduce plant height due to stink bug damage.

A high incidence and damage by *D. melacanthus* has also been verified in the V6 vegetative stage, which is consistent with the work of Copatti and Oliveira [14]. In their study, they show a high potential for damage to maize, which occurs in the initial state of development between V2 and V8. In other similar works, the reduction in plant height was not significant between conventional and transgenic hybrids, but rather it is a behaviour between varieties [15]. In another similar work, it is highlighted that the height of maize plants is not affected in any of the population and infestation of *D. melacanthus* [16].

As verified in this study, significant damage in maize is observed especially if the infestation occurs in the physiological stages V1 and V3, negatively affecting crop production [6], confirming a decrease in maize yield. (kg/ha) by increasing the number of green-bellied bugs per square meter, as observed in this research. In other similar works, the damage to the productivity components themselves is observed with field infestations of 2 and 4 bugs per m<sup>2</sup> [17]. Despite the reduction in plant height in conventional hybrids, no effects on productivity are observed, thus being the main factor in yield reduction due to a high infestation of *D. melacanthus* [12].

The same authors did not observe a relationship between the average weight of 100 corn kernels and the density of *D. melacanthus*. However, a negative relationship was revealed between the average weight of the spikes and the population densities of *D. melacanthus.* However, the grain yield decreases with the increase in the levels of infestation of stink bugs, evidencing that the increase in the population density of the insect reduces the weight and yield of grains in the corn crop. Bridi et al. [16] highlight that the reduction in productivity is 7.1% for each *D. melacanthus* added in 1 m<sup>2</sup> , in a range of 0–4 stinkbugs per m2 .

Portela et al. [18] obtained similar results, where they verified that the greenbellied bug causes a greater intensity of reduction in the weight of the maize grain when compared to the brown bug *Euschistus heros*, evidencing that the first species potentially cause greater damage to this crop than the second.

Bridi et al. [16] highlight the reduction of grains of up to 3.96 grains per row, which represents a decrease of 12.3% for every 4 stinkbugs per m2 compared to the absence of it. The length of the spike is also affected by the infestation of 3.16 stinkbugs, which causes a reduction of about 12% in relation to the size of the spike without the presence of the insect. In other similar works such as that of Cruz et al. [19], it is described that without the presence of the insect, the yield was 8048.43 kg/ ha, while, in the presence of the insect, the grain yield was 6352.21 kg/ha, a difference of 21.07% or 1696.22 kg/ha.

According to Duarte et al. [6], it is possible to estimate that the level of economic damage for *D. melacanthus* in the corn crop is 8 bugs/m2 , population density above which pest control is economically justified. These results disagree with those obtained by Bridi et al. [16] where they indicate that between 1 and 4 bugs per m2 significantly affects corn yield.

*Productive and Economic Losses Caused by* Dichelops melacanthus *in Transgenic Bt Maize… DOI: http://dx.doi.org/10.5772/intechopen.112390*

The insecticide commonly used to control bugs in corn is Imidacloprid. Research carried out by Chiesa et al. [8] show that this product can reduce the population density of the bug between 23.2 and 61.8% also that seed treatment with this insecticide does not efficiently protect against the attack of the bug *D. melacanthus*.

Albuquerque et al. [20] show that Imidacloprid may not be efficient when applied 8 days after the emergence of corn plants. Also, pre-emergence insecticide sprays have little effect on *D. melacanthus*, while post-emergence applications can achieve up to 80% control [21].

Another reason that may favour the high incidence of *D. melacanthus* is high temperature. The *D. melacanthus* bug performs better in high-temperature conditions (up to 31 ± 1°C) while constant temperatures of 19°C harm it. It has also been shown that Bt events such as transgenic soybeans do not affect their biology [22].

In several studies it has been shown that the treatment of corn seeds does not efficiently protect against the attack of *D. melacanthus*, also that the series of applications of chemical products in the vegetative and reproductive stages does not efficiently reduce the population density of the green-bellied bug. According to Modolon et al. [23], control plants without chemical seed treatments can present up to 100% of the plants attacked by *D. melacanthus*. On the other hand, Brustolin et al. [21] recorded up to 60% of plants attacked by *D. melacanthus* without seed treatments, while with treatments, the number of attacked plants can be reduced to 24%.

### **5. Conclusions**

Most of the Bt maize plants (80.7%) were attacked by *D. melacanthus*. Which reduced productivity and economic income.

*Dichelops melacanthus* caused an average of 6.1 punctures per Bt maize plants, affecting grain yield by 23% and causing a loss of income of 98.93 US dollars per hectare.

Average kernel weight of Bt maize plants was reduced due to damage caused by *D. melacanthus*. However, the reduction in the average height of Bt maize plants was not significant.

In future research, it is recommended to evaluate the effect of the attack of the bugs in the reduction of leaf area and photosynthetic capacity that reduces maize production. Other control methods for *D. melacanthus* should also be evaluated.

### **Acknowledgements**

National Council of Science and Technology (CONACYT, Paraguay) and National Program of Incentive for Researchers (PRONII), PROCIENCIA.

### **Conflict of interest**

The author declares no conflict of interest.
