Study of Effect Ultra-Violet Rays on Egg Hatching of the Sunn Pest Eurygaster testudinaria

A particularly damaging bug species for wheat plants is the sunn pest (Eurygaster testudinaria) (Geoffroy) (Hemiptera: Scutelleridae). It makes the wheat lose its ability to make pasta and bread (Ilcin and Celik., 2021). It is currently necessary to investigate alternate, non-toxic pest management strategies due to the usage of pesticides and the environmental effects that follow. The advantages of irradiation over chemical pesticides, such as its absence of residue, make it a well-established method for reducing insects (Ahmed et al., 2021). Programs for integrated pest management (IPM) have effectively employed this nontoxic and ecologically friendly technique to control insects (Ben-Yakir et al., 2013; Hajjar et al., 2023; Jabbar et al., 2023). The UV light is germicidal and is used to control insects. It is employed in physiological and embryological research as a beetle attractant and as an external disinfectant for insect eggs. In addition, Bhardwaj et al. (2019); Klingler and Bucher (2022) discovered that shorter wavelengths of UV had a greater inhibitory impact on organisms, causing the 305–315 nm region to be the highest for biological activity of solar UV radiation (Coohill and Sagripanti, 2009; Banaszak and Lesser, 2009). Insect interactions with plants are negatively impacted by UV-B radiation through the activation of photomorphogenic alterations and their detrimental effects on insect behavior and health (Kuhlmann and Müller, 2011; Yin et al., 2018). The most active and potentially harmful kind of radiation is UV-C, which has a wavelength range of 100 to 280 nm (Pattison and Davies, 2006). Due to this, some researchers are now exploring the prospect of employing UV radiation to prevent the growth of certain bug species, or at the very least to slow their growth (Faruki and Kahn, 1993; Sharma and Dwivedi, 1997). UV-C has been shown to be effective against several beetle and mite pests in stored products, with varying sensitivity depending on the period of exposure and the species of insect (Lah et al., 2012; Tungjitwitayakul, 2022).

Irradiation damage is becoming a well-known method for killing insect eggs. It is used in physiological and embryological studies as a beetle attractant and as a surface disinfectant for insect eggs (Bhardwaj et al., 2019). Eggs of Callosobruchus maculatus exhibited an inverse relationship with UV exposure. Gradually fewer pulse beetle eggs hatched as the amount of time they were exposed to radiation increased (Sedaghat et al., 2011). From a pest control perspective, significant reductions in egg hatching and adult emergence brought about by UV irradiation are advantageous. UV light affects the pulse beetle’s biological characteristics (Heidari et al., 2016).

Many biological creatures are stressed as a result of UV radiation (Schauen et al., 2007; Fu et al., 2012). It enters cells and causes photo-excited states in cell photosensitizers. Ultimately, it produces reactive oxygen species, which harm proteins, membrane lipids, and nucleic acids (Juan et al., 2021). Mutagenesis, changes to cell communication routes, and cytotoxicity are all examples of UV damage to cells. They all have significant impacts on many biological and cellular functions (McMillan et al., 2008). UV rays have also been demonstrated to influence various biological processes in insects, such as embryonic physiology, biochemistry, and behavior (Meng et al., 2010). In addition, UV rays damage insects photoreceptors and induce oxidative stress (Meyer-Rochow and Mishra, 2007). The objective of the current study was to ascertain how UV radiation affects E. testudinaria hatchability utilizing a non-chemical method that causes greater qualitative and quantitative damage.

The mature sunn pest E. testudinaria insects were gathered from wheat fields in Al-Muthanna Governorate, Iraq and transported to the laboratory of Agricultural Faculty, Al-Muthanna University in April 2024. The insects were positioned into 25 × 35 × 18 cm plastic cages and covered with muslin fabric, which had a rubber band fastened to it. It was maintained at 27±1°C, 60±10% R.H., and 16 L: 8 D photoperiod on wheat seeds, with moist cotton pieces added to the rearing container to give the insects a water supply, as described by Allahyari et al. (2010). The process was repeated using the laid eggs to establish an insect colony for the sunn pest sufficient to sustain the basic colony. Ten pairs (males and females) in plastic containers containing wheat plants 10-15 cm long for feeding purposes. Insects were left inside the containers to mate and lay eggs under laboratory conditions.

UV germicidal lamp 6-watt using a source for irradiation (TUV 6W G6T5, Philips, Poland) measuring 226 mm, emitting irradiation at a wavelength of 254 nm. An exam chamber (90 × 60 × 55 cm) has the lamp fastened to the ceiling. Three replicates, each consisting of 14 eggs, were placed in a petri dish. Before the egg masses were exposed to UV light in the experiment, they were captured from above using a digital microscope camera. The eggs were subjected to UV-C irradiation for 0, 5, 10, and 15 minutes each, while they were kept 5 cm away from the UV lamp’s surface.

An analysis of variance conducted in one direction was used to identify the data collected from the various time points (ANOVA; GenStat Release 12.1), followed by an LSD multiple range test. Notable variations in the tissues between the treatment and control groups (UV-C irradiation) were identified by an independent-sample t test (GenStat Release 12.1). The eggs’ hatchability percentages were computed using (El-Shennawy et al., 2019). Using the following equation:

The percentage reduction in egg hatching in comparison to the control was calculated using (Faruki et al., 2007) by using the formula:

Where, X₁ = average hatching rate of control eggs and X2 = average irradiated egg hatching.

The current study assessed the effects of UV-C radiation on E. testudinaria eggs. The results on hatchability percentage Table 1 and Figure 1 indicated that the hatchability percentage on different treatments varied between 2.38 % and 97.61%. The maximum hatchability percentage was observed on the control (97.61%) followed by 5 min (30.95%). With the lowest hatchability recorded, the most successful treatment was 15 minutes (2.38%), followed by 10 minutes (16.66%). Treatment times of 5, 10, and 15 minutes range from least to most effective. Table 1and Figure 1 . The regression equation obtained for hatchability includes Y= 111.9 - 29.998X. According to the formulae, hatchability was reduced by 29.998% after one minute of exposure to UV radiation, with an intercept of 111.9. The present findings showed that UV-irradiation reduced hatching of eggs; as exposure times rose, the impact became progressively greater. In addition, all UV-radiation exposure periods reduced egg hatching when compared to controls. This result is in agreement with the result of El-Shennawy et al. (2019), who noticed a positive correlation between the duration of UV radiation and Tribolium castaneum egg mortality (Sedaghat et al., 2011; Mirshekar et al., 2020). They reported that the proportion of Callosobruchus maculatus and Ephestia kuehniella eggs hatching decreased gradually as the length of irradiation exposure increased. According to Guerra et al. (1968), when Heliothis virescens and Helicoverpa zea eggs were subjected to short-wavelength UV radiation, the proportion of eggs that hatched declined over time and did not hatch after 20 minutes. C. maculatous eggs, on the other hand, were not UV-sensitive; some larvae finished their life cycle even after being exposed to UV-C for 50 minutes (Heidari et al., 2016).

According to our research, one possible cause of the reduction in egg hatchability is the nature of the UV-C effect on early developmental stages of insects, which is attributable to UV radiation transfer into animal tissues. UV rays have the ability to disrupt DNA directly or indirectly by causing reactive free radicals to develop, which can lead to oxidative stress, cytotoxic and mutagenic effects and other problems with cellular function in addition UV radiation ultimately inhibits egg hatching by cussing damages the egg chorion and leakage egg fluid (Ahmed, 2005; Güven et al., 2015).

Table 1: Different exposure times to UV radiation affect the hatchability and reduction in hatching percentage of E. testudinaria.

In Table 2 the correlation analysis showed a strong negative liner that the relationship between the amount of time spent exposed to UV radiation and hatchability was non-significantly inverse (-0.92). The linear regression coefficient for hatchability was -5.99.

Table 2: correlation and regression coefficient between UV radiation exposure duration and E. testudinaria egg hatchability.

The following conclusions were derived from this study regarding the effects of ultra violet irradiation on egg hatching of E. testudinaria: Increased exposure time to UVC radiation reduced egg hatching significantly. Thus, As a result this radiation UVC 254nm can be used insecticidal activity against E. testudinaria eggs. to suppress the population of certain insect pests without leaving a hazardous trace. However, more comprehensive research is needed on the impact of these rays and their relationship to climate change occurring in the world.

The author is grateful to the farmers for helping in wheat fields.

This research is critical for determining the effect of UV radiation on the most important pest in wheat fields, Sunn Pest. For future studies with climate changes occur in the world and Iraq specifically.

The author has declared no conflict of interest.