Effect of different locally available botanicals against stored cocoon pest, Dermestid Beetle

Introduction

Sericulture is an agro-based cottage industry which requires lowest investment and has high employment generation capacity. This activity generates high income which helps rural masses for improving their economic position (Hiware, 2001) [8] . Asia is the major producer of silk in the world and produces over 98.5 percent of the global output, although there are more than forty countries on the world silk map, but the bulk of silk comes from China and India followed by Brazil, Uzbekistan, Thailand, Vietnam, Korea and Japan (Bhat, 2014) [4] . India has a unique distinction of cultivating all the four types of silks which are commercially known varieties of natural fibers viz., Mulberry, Tasar, Eri and Muga. Among them, the mulberry silk is produced by the mulberry silkworm, Bombyx mori L. and it occupies a giant share of country's raw silk production. Mulberry sericulture is mainly practiced in five states namely, Karnataka, Andhra Pradesh, West Bengal, Tamil Nadu and Jammu & Kashmir, which jointly account for about 96.37 percent of the total mulberry raw silk production in the country. Sericulture is an agro-based industry. It involves Cultivation of mulberry Plants and rearing of Silkworms for the production of raw silk. Sericulture provides gainful employment, economic development and improvement in the quality of life to the people in rural areas and therefore it plays an important role in antipoverty programme and prevents migration of rural people to urban areas in search of employment.

In Jammu and Kashmir sericulture is a subsidiary occupation and is mainly practiced in spring season and the cocoons are sold after a period of storage as there is no ready market available. So during this period of storage cocoons are attacked by a number of insect and non-insect pests. Among various insect pests dermestid beetles are of particular importance, posing a great threat to silk industry. The dermestid beetles mainly damage stifled and stored cocoons, raw silk and silk fabrics. In grainages the dermestid beetles damage live cocoons kept for production of new generation of moths, seed (silkworm eggs) and live caterpillars. Exceptionally Dermestes maculatus Degeer was reported in Italy as a vector of pebrine disease of silkworm caused by Nosema bombycis Nageli (Candura, 1931) [5] . Hinton (1945) [7] recorded 19 species of Dermestidae as pests of silkworm in India. Thiagarajan and Govindaiah (1987) [19] reported 20 percent loss in a Mysore grainage due to this pes. The reelers purchase a huge quantity of cocoons from the farmers from the market occurring only once in a year and store it for a period of 8 to 10 months before further processing hence, encounter a great economic loss due to the dermestid beetle attack. In silk industry, the chemical insecticides like Deltamethrin solution helps to reduce the pest infestation. Fumigation with Methyle Bromide (0.5g/3m2) effective in controlling the pest.

Chemical insecticides can also be used against dermestid beetle but the associated risks involved like cost, poisoning, other health issues and environmental pollution etc overweigh the benefits. In order to reduce those risks exploration of naturally occurring plant material has achieved paramount importance in pest and disease management. The importance of research on eco-friendly, natural and biological source have been realized in recent years due to hazards of toxic chemicals on human beings and animals, that are being used in management of diseases and pests (Jagannanthan and Narasimhan, 1988) [9] . Use of botanicals for stored cocoon and other silk products are nontoxic, biodegradable and non-pollutant and will serve as an alternative strategy for management of post-harvest pests in sericulture. Thus the present investigation was undertaken to evaluate the effect of locally available botanicals on mortality, repellency, emergence and antifeeding effect of dermestid beetles.

Material and Methods

Culturing of dermestid beetle:

The dermestid beetles were collected from naturally infested cocoons from reeling units /fields/cocoon banks etc and were mass reared on silkworm pupae in insect cages. To have new progenies cotton wool was placed in each jar to induce oviposition. After incubation the dermestid grubs were used for the study.

Collection and processing of material:

The plants were collected in their fresh form then washed with water to remove the adhering material like dust. The material was shade dried and later on dried in hot air electric oven at 60°C till it attained a constant weight and was fit to be powdered, then was powered separately with the help of a mixer. Ten grams from each of the sample (powder) was taken and mixed with 100 ml acetone. The mixture was stirred for 30 minutes by a magnetic stirrer (at 3000 rpm) and left for 24 hours at room temperature. The mixture was filtered through a fine cloth before filtering through Whatman No. 1 filter paper. The filtrate was taken into a round bottom flask and condensed by evaporation of the solvent in a water bath at 45°C temperature so as to obtain a volume of 10 ml. The extracts were then preserved in an airtight bottle labelled and stored in refrigerator for future use.

Preparation of stock solution:

Stock solution of plants extracts was prepared separately by diluting the plant extracts with the distilled water to get desired concentrations viz; 5, 10 and 20 percent.

Method of application of prepared stock solution:

For each experiment per treatment per replication 15 grubs were released into each cage containing 30 pupae. The openings of the plastic cages were secured with netting material. Desired concentration of prepared solution was applied to the grubs. Each treatment was replicated three times and the number of dead grubs was counted after 24 hours, 48 hours and 72 hours to determine the mortality rate of dermestid beetle grubs.

Repellence test:

This was conducted as per (Akinwumi et al., 2007) [2] . Plastic containers approx. of 25x12x10 cm were used for the investigation on repellency. An aliquot of different concentrations of each of the plant extracts was rubbed thoroughly on the skin of pupal samples. The samples treated with each of the plant extract were placed separately at the center of each of the plastic container. This was immediately followed by the introduction of 15 dermestid grubs. The grubs used in this study were pre-starved for forty-eight hours before introducing them into the containers. Daily observations were made for five days immediately after application and the number of dermestid grubs found on and away from treated pupae were recorded.

The average count was expressed as a percentage of repellency.

Observations recorded: Corrected mortality:

For calculation of corrected mortality rate Abbott's formula was used

Repellency test:

The data is expressed as percentage repulsion (PR%) by using the following scale described by Laudani et al. (1995) [11] .

Weight loss of treated pupae:

The weight loss of treated pupae caused by dermestid beetles infestation was calculated by using the formula:

Emergence of treated grubs:

The adult emergence of treated grubs was calculated by using the formula:

Results and Discussion

Mortality percentage

The results of mortality percentage of dermestid grubs at different hours, treated with different botanical extracts with different concentrations have been summarized in Table-1.

The application of different botanical formulations showed significant effect on the mean mortality percentage of dermestid grubs at different (HAT), ranged from (80.43-11.06) which was higher as compared to control group.The maximum mortality percentage, irrespective of the botanicals were observed at 20 percent concentration at 72 HAT (hours after treatment).Significantly the higher mortality percentage (97.83%) was observed in B1 (Capsicum annum) at 72 HAT followed by B4 (Pyrethrum) and B2 (Artemesia absinthium) with 81.93 and 53.83 percent respectively. While as B3 (Datura stramonium) showed 33.23 percent mortality. However the lowest mortality percentage 13.33 percent was recorded in control group. During the present study, in B4 (pyrethrum) the rectal protrusion was noticed in some of the treated grubs. However the grubs treated with each of the tested botanical became paralyzed immediately after the application and turned black before their death. The extract of B1 (Capsicum annum) recorded the fastest action in killing and kills (80.16%) of the dermestid grub population within 24 hours of treatment even at 5 percent concentration while as the B3 (Datura stramonium) extract was the least toxic to the dermestid grubs even at increased dose of 20 percent concentration. This observation is in conformity with the studies of Nowsad et al. (2009) [13] who reported the higher mortality percentage of adults of dermestid species treated with red chili when compared to neem and garlic extracts. He further reported that mortality percentage increased with an increase in time and concentration. This study is also in harmony with the results of Saranya et al. (2019) [16] who reported (33.33% to 56.67%) mortality of Dermestesater grubs on application of plant extracts of various botanicals. He also reported that mortality percentage increased significantly with an increase in time and concentration. In Capsicum annum highest mortality might be due to the presence of Capsaicin as reported by Antonious et al (2006) [3] .

In the present study the toxic effects like rectal protrusion was also observed in some of the Pyrethrum treated grubs.

The insecticidal activity of Pyrethrum is due to the presence of esters called pyrethrins which includes the pyrethrin I & II as reported by Wenli et al (2020) [18] and the dermestid grubs became paralyzed immediately after the application and turned black before their death. These observations are in line with the observations of Copping (2001) [6] who reported that, in insects Capsaicin toxicity appears to be through metabolic disruption, membrane damage and nervous system disfunction. The increased mortality percentage in Artemesia absinthiumwhen compared to the control might be due to the main active ingredients present in Artemesia absinthium i.e. α-Thujone and β-Thujone as reported by Vourch el al (2002) [20] , Maia et al (2011) [12] , Rojht et al (2009) [15] and Sener et al (2009) [17] . The increased mortality percentage in Datura stramonium when compared to the control might be due to active ingredients present in its seed extracts as reported by Abbasipour et al (2011b) [1] .

Repellency percentage

The results of repellency percentage of dermestid grubs are summarized in table-2.

After the release of dermestid grubs on the silkworm pupae treated with different botanical extracts. The dermestid grubs repelled much more rapidly from the treated pupae then the control. There was a significant difference in repellency percentage of dermestid grubs from the beginning to the end i.e. from day 1st to day 5th after application of different botanical extracts in all the treatment groups when compared to control.

The repellency percentage increased progressively with increasing concentration but decreased with time of exposure in all the four tested botanicals. Significantly, the repellency effect of botanical extracts on dermestid grubs was higher in 20 percent Capsicum annum extract from day 1st to day 5th (42.13%-37.56%) followed by Pyrethrum (35.90%-35.03%) and Artemesia absinthium (32.66%-32.03%). The lowest repellency percentage was recorded on control (6.03%-4.83%), followed by Datura stramonium (32.83%-30.83%) from day 1st-day 5th of treatment.

On the basis of mean repellency, the repellency class for capsicum annum at 20 percent concentration came to be class III while as Artemesia absinthium, Datura stramonium and Pyrethrum came under class II of repellency. These results are in line with the earlier reports of Nowsad et al. (2009) [13] who reported significant repulsion percentage i.e. 38.44 percent in red chili, followed by neem (62.67%) and garlic (33.33%) when compared to control. These results are also in harmony with the findings of Luke et al. (2018) [14] who reported the significant repulsion percentage of dermestid grubs in all the tested botanicals when compared with the control.

In Capsicum annum highest repulsion percentage might be due to presence of Capsaicin as reported by Antonious et al.

(2006) [3] . The results of repulsion percentage of dermestid grubs increased progressively with increase in concentration and decreased with the increase in time in all the tested botanical extracts. These results correlate well with the earlier reports of Nowsad et al. (2009) [13] and Luke et al. who reported significantly higher repulsion percentage of dermestid beetle in botanical treated batches with increase in concentration and the percentage of repulsion decrease with the increase in the time of exposure when compared with the control.

Significantly the increased repellency percentage of dermestid grubs in all the tested botanical extracts might be due to the smell of repellent compounds present in them as reported by Sener et al (2009) [17] . Therefore due to the smell of repellent compounds the grubs accelerate their moment away from the treated silkworm pupae. These results collaborate well with the earlier results of Keelar (1999) [10] and Luke et al. (2018) [14] who found significant difference in mortality of grub and adult emergence of Dermestes maculatus treated with the botanical extracts of Afrostyraxkamerunensis, Monodoramyscistica, Moringa oleifera and Azadirachta indica.

In the present study the emergence was totally inhibited in Capsicum annum treated batches at all the concentrations used and in Pyrethrum 100 percent adult emergence was also totally inhibited at 20 percent concentration. These results also coincide with the results of Luke et al (2018) [14] who reported zero percent emergence of Dermestes maculates in Afrostyraxkamerunensis and Azadirachta indica treated batches al all the concentrations used.s The inhibition in adult emergence of dermestid beetle species treated with different botanical extracts might be due to insecticidal property of active ingredients of these tested botanicals, which causes metabolic disruption, membrane damage and nervous system dysfunction as reported by Copping (2001) [6] .

Probit analysis of mortality percentage of grubs

The result of the probit analysis for the estimation of LC 50 values and fiducial limits at 72 hours of treatment for the mortality of dermestid grubs are presented in table 5.

The LC 50 value of Capsicum annum, Artemesia absinthium, Datura stramonium &pyrethrum were 0.44, 0.97, 1.13 & 0.5 ml per 10ml solution respectively at 72 hours after treatment, which indicates that capsicum annum was the most toxic against dermestid species. The application of 4.4% of Capsicum annum extract helps to kill 50% of the population of dermestid beetle species.

In the present investigation the LC 50 values of Capsicum annum, Artemesia absinthium, Datura stramonium and Pyrethrum were 0.44, 0.97, 1.13 & 0.5 ml per 10ml of solution respectively at 72 hours after treatment, which indicates that capsicum annum was the most toxic to dermestid species. The results of LC 50 are in line with the findings of Nowsad et al (2009) [13] who reported the lowest LC 50 value i.e 1.11 percent in red chili followed by neem and garlic.

Conclusion

On the basis of above findings, it is concluded that the extract of Capsicum annum is the best bio-insecticide, it has the highest repellent and toxic effect against dermestid species. Thus the application of ecofriendly and locally available Capsicum annum extract for disinfection of cocoon storage rooms/ bags can help the silkworm rearers/ reelers to reduce the post storage loss of silkworm cocoons.

Funding

The authors received the financial support extended for conducting the present investigation from the college of temperate Sericulture, Sher-e-Kashmir University of Agricultural Sciences &Technology of Kashmir, Shalimar Srinagar (J &K)190025

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