The investigation on 'Evaluation of Copper Nanoparticles against Spodoptera litura' was conducted at the Department of Entomology, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola, during the 2023–24. The study utilized a completely randomized design (CRD) with eight treatments, each treatment replicated thrice involving 30 larvae per treatment. The treatments included five different concentrations of CuNPs: 10, 50, 100, 300, and 500 ppm, insecticide chloropyriphos 20 EC, control (acetic acid) and control (distilled water). The results indicated that CuNPs showed significant efficacy compared to the control treatments, exhibiting larvicidal properties. Larval mortality ranged from 4.44 percent to 74.44 percent when assessed by using the leaf dip method, and 6.67 percent to 68.89 percent with the larval dip method. Amongst the CuNPs, at a concentration of 500 ppm, highest larval mortality in S. litura was recorded by both leaf dip and larval dip method. Result showed that copper nanoparticles are lethal to Spodoptera litura. (Published in International Journal of Advanced Biochemistry Research 2024; 8(10): 286-289. DOI: 10.33545/26174693.2024.v8.i10d.2462)
Introduction
The tobacco caterpillar, Spodoptera litura is one of the economically important and regular polyphagous pests on the field and horticultural crops (Murthy et al., 2006). The pest can potentially induce yield losses ranging from 35%–55% during crops' blossom and vegetative stages (Rao et al., 2014). Among the main crop species attacked by S. litura in the tropics are Colocasia esculenta, cotton, flax, groundnuts, jute, lucerne, maize, rice, soyabeans, tobacco, vegetables (Brassica, Capsicum, cucurbit vegetables, Phaseolus, potatoes, sweet potatoes, etc.). Now a day it has been reported that S. litura can feed on over 380 plant species (Wu et al., 2019).
Generally chemical pesticide are used to control the larval population but now a day the management of tobacco leaf eating caterpillar is becoming a major challenge to farmer because of day by day the species attains resistance against different common insecticide. The widespread use of chemical insecticide and pesticide harms the non-targeted species and the green ecosystem. A direct effect of synthetic chemicals on human health and nontargeted species is currently evident. Furthermore, chemical pesticides are lost during application due to volatization, oxidation and photolysis, with less than 0.1% of that product being effective against target organisms. To address the above issues an innovative updated approach to insect pest control is needed.
Nanotechnology offers a new agrochemical and distribution technology and reduces the doses of insecticide to crop production. At present the available insecticide helps in increase in productivity but requires high dose to suppress the pest population (Khan et al 2017), and nanotechnology aims to reduce the doses through encapsulation and coating (Ayyaril S. S., et al 2023). The Copper based nanomaterials gained importance in agriculture in terms of plant protection for the control and management of various pests, weeds, and plant diseases caused by an array of bacterial, fungal, and viral plant pathogens. Since copper is cheaper and more accessible than other nanomaterials, it is a cost-effective way to control insect pests in agriculture (Garcia et al 2014). The copper oxide NPs showed high mortality rate in Spodoptera littoralas larvae. NPs affect eggs laid in females and modify the sex ratio in female and male. In addition, copper nanoparticles can be easily mixed with polymers and are relatively stable in environmental conditions (Shaker et al., 2016). The copper-based nanomaterials are also utilized as insecticide and larvicide against plant insect pests such as leaf worms, mealybug, thrips, stored grain pest, spider mite; and various mosquito vectors.
Materials and Methods
The current study was conducted in the Toxicology laboratory of Department of Agriculture Entomology, Dr Panjabrao Deshmukh Krishi Vidyapeeth, Akola during the year 2023–24. Tobacco eating caterpillar, Spodoptera litura larvae were collected from the sunflower crop grown at Oilseed Research Unit, Dr. PDKV, Akola. Larvae were reared under the laboratory condition on castor leaves; larvae were kept at approximately 27±2°C and at 70±5 percent humidity.
Evaluation of copper nanoparticles on larval mortality of Spodoptera litura was done by using two methods: leaf dip and larval dip method. For the leaf dip method (as per Rahman et al., 2022), castor leaves were treated with different concentrations of copper nanoparticles (10, 50, 100, 300, and 500 ppm) and air-dried before being used for feeding for 10 minutes. The castor leaves were also treated with the insecticide chlorpyrifos 20 EC at a concentration of 2 ml/L, as well as control treatments of distilled water and acetic acid. Healthy second-instar larvae were introduced into petri plates containing the treated leaves, following a 24-hour starvation period. Each experimental group contained 30 larvae. Larval mortality was noted till the 6th day after treatments.
For the larval dip method, different concentrations of copper nanoparticles were prepared (10, 50, 100, 300, and 500 ppm). Larvae were dipped individually in the above mentioned concentrations of copper nanoparticles and air-dried for 10 min. The treated larvae were introduced to the petri plates containing fresh castor leaves. Similarly, larvae were treated with the insecticide chlorpyrifos 20 EC @ 2 ml/L, as well as control treatments of distilled water and acetic acid. Each experimental group contained 30 larvae. Larval mortality was noted till the 6th day after treatments. Larval mortality was calculated using the formula: Per cent of mortality = (No. of dead larvae / No. of larvae introduced) × 100.
Results and Discussion
All the treatments were significantly superior over control treatment by leaf dip method. Highest larval mortality of 93.33 percent was recorded in Chloropyriphos @ 2 ml/L and found superior over the treatments comprising CuNPs. Among CuNPs treatments, larval mortality was initiated at 24 hr after treatment — 14.44 percent by CuNPs 500 ppm and 8.89 percent by CuNPs 300 ppm. Larval mortality was also recorded at CuNPs 50 and 100 ppm concentration. It was observed that larval mortality increases as concentration of CuNPs increases. At higher concentration (500 ppm) about 74.44 percent larval mortality was recorded on 6th days after treatment (DAT) followed by 300 ppm of CuNPs with 47.78 percent larval mortality. The control treatment remains unaffected with no larval mortality.
By larval dip method, highest larval mortality of 95.56 percent was recorded in Chloropyriphos @ 2 ml/L treatment. Among CuNPs treatments, initiation of larval mortality was noticed at 24 hr after treatment — 17.78 percent by CuNPs 500 ppm and 8.89 percent in CuNPs 300 ppm. CuNPs @ 500 ppm recorded highest 68.89 percent larval mortality at 6th days after treatment followed by CuNPs 300 ppm with 51.10 percent larval mortality. No larval mortality was recorded in control treatment. The results demonstrated that CuNPs exhibited notable larvicidal activity, with higher concentrations resulting in increased larval mortality when applied by both leaf dip and larval dip methods.
The findings reveal that higher dose of CuNPs treatment led to significant larval mortality compared to the untreated control. The highest mortality was observed at CuNPs @ 500 ppm and 300 ppm, which aligns with previous studies suggesting a dose-dependent response to nanoparticle treatments (Azzay and Ghani, 2023). The findings are supported by Tahir et al. (2022), who revealed that larval mortality increases with higher concentrations of copper nanoparticles (CuNPs). Additionally, Rahman et al. (2022) demonstrated that CuNPs significantly impacted the larval mortality of Spodoptera frugiperda. Atwa et al. (2017) indicated that copper nanoparticles (CuNPs) do not exert an immediate lethal effect on insect mortality but rather exhibit a cumulative effect over time, aligning with our study where the impact of CuNPs on insect mortality appears to build progressively rather than manifesting as a sudden increase in lethality. This cumulative effect may result from various factors, including prolonged exposure to CuNPs leading to bioaccumulation and subsequent disruption of physiological functions. Chlorpyrifos 20 EC, a chemical insecticide, demonstrated higher mortality. Amongst the CuNPs, higher concentration caused higher mortality in S. litura. This comparison suggests that CuNPs can be used as an alternative to the traditional insecticides, making them an attractive alternative for sustainable pest management.
Conclusion
Copper nanoparticles (CuNPs) exhibited significant effectiveness in managing Spodoptera litura, particularly at higher concentrations of 500 ppm. Both leaf dip and larval dip methods are effective, highlighting the importance of application technique of CuNPs in pest management strategies. These findings underscore the potential of CuNPs as a viable alternative to traditional chemical insecticides.