Entomology, Ornithology & Herpetology: Current Research
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Effectiveness of Some Chemical and Biological Pesticides against Sitophilus zeamais (Motschulsky)

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Abstract

The study on “Effectiveness of some chemical and biological pesticides against S. zeamais” was carried out at National Entomology Research Center, NARC, Khumaltar, and Lalitpur. This study was carried out to find the residual effect of the pesticides on S. zeamais mortality. Each pesticide was applied in 3 concentrations.: Emmamectin Benzoate @0.3 ml/ltr, @0.1 ml/ltr and @0.6 ml/ltr, Neem @5 ml/ltr, @2.5 ml/ltr and @10 ml/ltr, Chloropyrifos (50%)+Cypermethrin (5%) @1.5 ml/ltr, @0.75 ml/ltr and @3 ml/ltr; and Malathion @2 ml/ltr, @1 ml/ltr and 4 ml/ltr. The residue of pesticide on weevil mortality was seen the highest on Chloropyrifos (50%)+Cypermethrin (5%) till the 87th Day and was least on Neem even on the 1^st day of observation. The mortality % was highest (100%) on Chloropyrifos (50%)+Cypermethrin (5%) and Malathion and was lowest (0%) on Neem. The maximum weight loss was observed on Neem @2.5 ml/ltr which was 9.4% whereas, minimum wt. loss was observed on Chloropyrifos (50%)+Cypermethrin (5%) @3 ml/ltr which was 0.25% of the total grain weight. The maximum percent of damaged grain was observed on Neem which was 100% while the minimum percent of damaged grain was observed on Chloropyrifos (50%)+Cypermethrin (5%) @1.5 ml/ltr which was 11.21% of the total grain. No weevil progeny emerged from Chloropyrifos (50%)+Cypermethrin (5%) @1.5 ml/ltr treated seeds whereas the maximum number of progeny emerged from Neem @2.5 ml/ltr treated seeds which were 149.67. Out of the 4 pesticides tested on the adult of Sitophilus zeamais, Chloropyrifos (50%)+Cypermethrin (5%) were found to be most effective while Neem was the least effective.

Introduction

Maize development is a lifestyle for most farmers in the slopes of Nepal. It is a traditional crop which is cultivated as food, feed, and fodder on inclining land which is rain-fed upland in the hills. It is developed under downpour took care of conditions throughout the mid-year (April- August) as a solitary yield or transferred with millet later in the season. In the terai, internal terai, valleys, and low-lying river basin regions, maize is likewise grown in the winter and spring with irrigation system [1]. Different cereal harvests have assumed significant parts intending to food security issues in Nepal. Lately, there have been vacillations in crop production and demand situations because of different reasons [2]. Maize is the second most significant yield after rice as far as region and production in Nepal. It is a lifestyle for the farmers of the hilly area in Nepal. It is a traditional yield developed for food, feed, and fodder. Maize demand has been continually developing by about 5% yearly in last decades. Per capita, maize consumption in Nepal was 98 g/individual/day. Winter maize under the rice-wheat system has been arising as another intercession and it tends to be a choice to expand maize production in Nepal [3].

The stored maize is attacked and harmed by a few pests that lead to quality fading driving farmers to sell at scaled down costs and underneath the production cost. Insect-Pests are frequently viewed as the main reason for maize grain losses. The main pests that cause harm to maize in the field and capacity are Lepidopterist stalk borers and Coleopterans weevils, respectively. In excess of 37 types of arthropod pests are related with maize grain in storage. During the storage time frame, insects -pests and diseases assume a huge part in diminishing production and productivity combined with germination potential.

Among pests, maize weevil (Sitopilus zeamais ) and Angoumois grain moth (Sitotroga cerealla ) were the main pests found in stored maize in Nepal. This happens on the grounds that the majority of the maize produced by farmers stays on the open floor of their room without keeping up appropriate storage standards. The primary reason for this is farmer’s absence of sufficient information in regards to the situation with insect pests in a stored condition [4].

S. zeamais Motsch stays quite possibly the most serious and internal feeding pests of maize. It falls among the most dangerous pests in stored grain, particularly maize in tropical areas. Grown-up female of weevils causes harm by drilling into the kernel and laying eggs (ovipositing). The larvae and pupae eat the inward pieces of the kernel, which brings about a harmed kernel and diminished grain weight. The pervasion boosts temperature and dampness content in the stored grain mass, which can prompt fungal growth, including toxigenic species, for example, Aspergillus favus Link. S. zeamais can cause an extensive loss in quality and amount of the grain on the field just as in the storage [5].

There have been different sorts of insecticides that have been suggested for the control of storage pests in Nepal [6]. In any case, direct utilization of such insecticides is neither relevant nor doable [7]. The chemical control is compelling, quick, secure, and conservative yet it has some significant downsides: adverse consequence on products and surrounding environment; the steady peril of intoxication for people and animals; the presence of residue in various pieces of the plants; appearance, at the pest species, of protection from pesticide [8]. Disposal of these downsides should be possible by utilizing some fewer contaminating insecticides, from the IIIrd and IVth groups of toxicity, and by utilizing efficient dosages, as least as [9].

Materials and Methods

The following experiment was conducted in the laboratory of the National Entomology Research Center of NARC, Khumaltar, and Lalitpur, Nepal. Rearing of S. zeamais was performed in a laboratory setting by maintaining appropriate temperature, and sanitary conditions. Firstly, about 1 kg of healthy, dry and pest-free maize of mixed variety was selected. For rearing Sitophilus zeamais (Maize weevil), a total of 5 cylindrical glass jar 16 cm × 8 cm were used. These cylindrical glasses were filled with 300 gm of a mixed variety of maize in each vessel. Fifty S. zeamais each (without separating male and female) were kept in each vessel for mating. Black muslin cloth of suitable length was used to cover the open end of the cylindrical glass jar. After a week the fifty S. zeamais which were kept for mating were removed from each of the vessels and the rearing of S. zeamais was started. After 30-35 days, adult S. zeamais started to emerge. The age of the weevil used in the experiments was of 1-7 days of age.

For the implementation of the experiment, 60 small, clean cylindrical plastic containers was taken and labelled using a permanent marker. The maize of mixed variety was selected, 50 gm each was placed in those 60 containers and was covered with their lids. Chemical pesticides and bio-pesticides were selected and prepared in appropriate quantity according to the requirement for the experiment. Altogether 5 treatments with 3 concentrations, each having 4 replications for each experiment. Each container was treated with a particular dose of treatment for 5 days. On the 5^th day, 10 weevils each was left into each container and was observed at the interval of 48 hrs. 10 new weevils was added to each container every 5 days interval discarding the previously added dead/alive until 25^th Day. In the later stage, 10 weevils were added to each container at the interval of 10 days. During this process, the weevils were discarded after each observation. This experiment was conducted for 87 Days.

After the completion of an experiment to find the residual effect of pesticide on weevil mortality, the data to observe the weight loss, damaged grains and no of weevil progeny were taken on 7 March 2021 which was a week after the final observation for weevil mortality of treatment 3 and 4 and 67 days after the final observation for weevil mortality of treatment 1 and 2 (Table 1).

Table 1: Description of different insecticide used in the experiment against Sitophilus zeamais.

The weight loss percentage was determined by the following
formula:

Similarly, the percentage of damaged grains was determined by the following formula:

The data was managed in the MS. EXCEL file. Later, two-way ANOVA was used to compare the mortality caused by different treatments and concentrations of different pesticide. Weight loss, damage % and the number of weevil progeny were also subjected to two-way ANOVA. The means were compared using Turkey HSD Test at 0.05 significance level (SPSS Inc., Chicago, II, USA).

Results and Discussion

During this experiment, each treatment had 3 concentration/doses i.e., Normal dose, half dose and double dose. The residual effect of different concentration of pesticides was found significantly different after twelve days to sixty-seven days for weevil mortality. Among the tested chemicals, the residue of pesticide on weevil mortality was seen the highest on Chloropyrifos (50%)+Cypermethrin (5%) till the 87^th Day. The residue of pesticide on weevil mortality was least which was (0%) with no mortality of any weevil population for all three concentrations of Neem even on the 1^st day of observation. i.e., on the 7^th Day. The maximum mortality for control treatments was observed on the 22^nd day which was 17.5% whereas the minimum mortality was 0% for all other days. Mortality percent of different concentrations was highly significant for the 12^th, 17^th, 22^nd, 27^th, 37^th, 47^th and 67^th Day among the concentrations (P<0.01). Similarly, the mortality percent were not significant for the 7^th, 57^th, 77^th and 87^th Day among the concentrations P (>0.01).The mortality percent of different treatments were highly significant for all the observations made on the 7^th Day till the 87^th Day among the treatments (P<0.01). The mortality percent of source (conc × trt) was highly significant for the 12^th day, 37^th day, 47^th day and 67^th day of observation among the different conc × trt (P<0.01). Similarly, the mortality percent was not significant for the observations made on the 7^th, 17^th, 22^nd, 27^th, 57^th, 77^th and 87^th day respectively among the different conc × trt P (>0.01) (Figures 1-3) (Tables 2 and 3).

Figure 1: Mortality percentage of weevil population on different days for three concentrations of Emmamectin Benzoate.

Figure 2: Mortality percentage of weevil population on different days for three concentrations of Chloropyrifos (50%)+Cypermethrin (5%).

Figure 3: Mortality percentage of weevil population on different days for three concentrations of Malathion.

Table 2: Mean mortality percentage (± SE) of Sitophilus zeamais due to the residual effect of various chemical and biological pesticides treatments on different days.

Table 3: Mean percentage (± SE) of weight loss of maize grains, Percentage of damaged grain (± SE) and mean number (± SE) of weevil progeny in different treatments of chemical and biological pesticides.

Cypermethrin (5%) and Emmamectin bezoate based treatments while the percent weight loss was very high in Neem based treatment. The percent weight loss of three different concentrations of Malathion was 2.97% for Malathion @1 ml/ ltr, 1.91% for Malathion @2 ml/ltr and 0.35 % for Malathion @4 ml/ltr. The percent weight loss of three different concentrations of Chloropyrifos (50%)+Cypermethrin (5%) was 3.16% for @
0.75 ml/ltr, 0.73% for @ 1.5 ml/ltr and 0.25% for @ 3 ml/ltr. Similarly, the percent weight loss of three different concentrations of Emmamectin bezoate was 2.41% for @0.1 ml/ltr, 0.9% for @0.3 ml/ltr and 1.46% for @ 0.6 ml/ltr. The percent weight loss was highest for Neem among all the other treatments which were 9.4% for @ 2.5 ml/ltr Neem, 3.74 for @ 5 ml/ltr Neem and 7.63% for @10 ml/ltr Neem. The weight loss percentage was seen highest in the control treatment after Neem which was 3.41% of the total weight.

The maximum percentage of damaged grain was observed on all three concentrations of Neem which were 100% for all the three concentrations. The minimum percentage of damaged grain was observed on Chloropyrifos (50%)+Cypermethrin (5%) @1.5 ml/ ltr which was 11.21% of the total grain. The percentage of the damaged grain of three different concentrations of Malathion was 79.23% @1 ml/ltr, 68.3% for @2 ml/ltr and 71.34 % for @4 ml/ltr. The percentage of the damaged grain of three different concentrations of Chloropyrifos (50%)+Cypermethrin (5%) was 14.51% for @ 0.75 ml/ltr, 11.21% for @ 1.5 ml/ltr and 14.35% for @ 3 ml/ltr. Similarly, the percent damaged grain of three different concentrations of Emmamectin benzoate was 39.2% for @0.1 ml/ltr, 69.9% for @0.3 ml/ltr and 38.73% for @ 0.6 ml/ltr. The percent weight loss was highest for Neem among all the other treatments which were 100% for @ 2.5 ml/ltr Neem, 100% for @ 5 ml/ltr Neem and 100% for @10 ml/ltr Neem. 61.63% of damaged grain was observed on the control treatment.

The F1 progeny emergence in different observations was significant among different management practices. The lowest number of weevil progeny emerged from Chloropyrifos (50%)+Cypermethrin (5%) @1.5 ml/ltr treated seeds was 0 whereas the maximum number of weevil emerged from the Neem @2.5 ml/ltr treated seeds was 149.67. The number of weevil progeny that emerged from three different concentrations of Emmamectin bezoate was 2 for @0.1 ml/ltr, 9.33 for @0.3 ml/ltr and 1 for @0.6 ml/ltr. The number of weevil progeny that emerged was highest for Neem among all the other treatments was 149.67 for @2.5 ml/ltr Neem, 81.5 for @ 5 ml/ltr Neem and 96 for @10 ml/ltr Neem. The number of weevil progeny emerged from three different concentrations of Chloropyrifos (50%)+Cypermethrin (5%) was 0.67 for @0.75 ml/ ltr, 0 for @1.5 ml/ltr and 0.33 for @3 ml/ltr. Similarly, the number of weevil progeny that emerged from three different concentrations of Malathion was 7.33 for Malathion @1 ml/ltr, 5.33 for Malathion @2 ml/ltr and 0.33 for Malathion @4 ml/ltr. The number of weevil progeny that emerged in the control treatment was 49.67 ± (3.51).

The weight loss and percent damaged grains were found to be significantly different among concentrations (P<0.01) whereas there was no significant difference in the number of weevil progeny P (>0.05). Similarly, all the three dependent variables; weight loss, Percent damaged grains and no of weevil progeny were found to be highly significant P (<0.01) among the different treatments. As for the source (Concentrations × treatment), the percent damaged grain was found to be highly significant (P<0.01) while weight loss and no of weevil progeny were not significant P (>0.01) [10].

Conclusion

Insects are often considered the principal cause of maize grain losses. Pests are one of the major constraints that limit the potentiality of maize in Nepal. They attack the maize plants directly from the seeds sown in the field during maturity and feed on all parts of the plants. The chemical control is effective, quick, secure and economical but it has some major drawbacks: negative impact on products and environment; the constant danger of intoxication for humans and animals; the presence of residues in different parts of the plants; appearance, at the pest species, of resistance to pesticide. Out of the 4 pesticides tested on the adult of Sitophilus zeamais, Chloropyrifos (50%)+Cypermethrin (5%) were most effective followed by Malathion, Emmamectin Benzoate and at last Neem. Neem treatment had a 0% mortality rate which showed no reduction of the weevil population, rather resulted in the highest no of progeny during the last stage of the data observation. This means these 3 pesticides except Neem can be recommended for control of Sitophilus zeamais. Chloropyrifos (50%)+Cypermethrin (5%) has a longer residual effect so that it could prevent damage from S. zeamais for a longer period which could be used to preserve maize seed. Pesticide treated grains should not be used for consumption purpose.

Acknowledgement

I would like to express by sincere thanks to Prof. Dr. Binayak Prasad Rajbhandari, Executive Chairperson, Himalayan College of Agriculture Sciences and Technology (HICAST), Kirtipur. I express my deep sense of gratitude to my thesis advisor Dr. Anupama Shrestha Shah, Adjunct Professor of HICAST, Kirtipur for her valuable guidance, and constructive suggestion at every stage of this study. I am extremely grateful to Dr. Sunil Aryal, Senior Scientist, NERC, and NARC for his continuous guidance during research tenure and thesis writing. I also acknowledge Ms. Resona Simkhada, Technical officer and Mr. Harka Balayar, Technical Assistant, NERC, NARC and Mrs. Kushum Shrestha who helped organizing material for smooth running of the experiment and the team for their encouragement and excellent guidance throughout the research duration.

Conflict of Interest

The authors declare no conflict of interest.

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