Silkworm Diseases and Management UNIT 2 SILKWORM PESTS AND THEIR MANAGEMENT

Structure

2.0 Objectives

2.1 Introduction

2.2 Identification of Pest

2.3 Life Cycle of Uzi

2.4 Uzi fly Management and Economics

2.5 Dermestes

2.6 Let Us Sum Up

2.7 Glossary

2.8 Suggested Further Reading

2.9 References

2.10 Answers to Check Your Progress

2.0 OBJECTIVES

After reading this unit, you will be able to:

z explain the major pests of silkworm, period of occurrence and their life cycle;

z identify the symptoms of pest attack and extent of damage; and

z discuss the methods to manage the pest and its profit.

2.1 INTRODUCTION

Before you try to understand about the pests of silkworm, you should know what a pest is? Any ( or non-insect) organism, which interferes with human welfare, leading to economic loss is termed a pest.

Especially related to silkworm crop, two important pests are found to cause economic loss. In the traditional producing states of the country, the silkworm in larval stage is attacked by a tachinid fly (Exorista bombycis), commonly known as uzi fly, leading to considerable decline in cocoon yield. In cocoon stage (seed / stifled / pierced cocoons), the silkworms are attacked by dermestid (Dermestes spp.) These beetles are commonly referred to as carpet beetles. They are reported to cause considerable reduction in egg production in silkworm egg production centers (grainages). 22 Silkworm Pests and 2.2 IDENTIFICATION OF PESTS their Management

Uzi Fly, Exorista bombycis (Diptera : Tachinidae) z The adult Uzi fly is blackish grey in colour. z It is bigger than the common , Musca domestica and is more efficient in flight. z It has four longitudinal black stripes on the dorsum of the thorax and three cross-wise stripes on the abdomen. z Male are 11.9 mm to 12.00 mm and the female 10.20 mm to 10.40 mm in length. Width varies from 3.60 to 3.90 mm. z Wing span is about 10 mm and the wings are covered with dark grey hairs. Eyes are chocolate brown in colour (Fig.2.1).

Fig.2.1: Adult uzi fly Fig.2.2: Female abdomen Fig.2.3: Male abdomen (Ventral) (Ventral) z The lateral margins of the abdomen are covered with bristles, which are thicker and longer in males than in females (Fig. 2.2 & 2.3). z Males can be easily distinguished from the females by the presence of external genitalia (pinkish brown in colour) at the tip of the abdomen on the ventral side and well developed tips of the legs (tarsal pads). 2.3 LIFE CYCLE OF UZI FLY A female lays 500 - 600 eggs during her life time (18 - 22 days), each day laying about 20-30 eggs. z Eggs hatch in 48 - 60 hours. z The Maggot after hatching from the egg immediately pierces into silkworm body using the pro-thoracic hook attached to the mouth. The place of entry of maggot into silkworm body develops a black scar. z The maggot feeds on the silkworm tissues for 5-7 days during which time it moults twice. z The maggot comes out of silkworm body by creating an opening on the body (integument) and spends 12-20 hours time as post-feeding (post- parasitic) maggot and becomes pupa in dark places like cracks, crevices, corners of the rearing house, loose soil, etc (Fig.2.4). 23 Silkworm Diseases and Pest Management

Parasitic maggot (5-7 days) Post-parasitic maggot (12-20 hours)

LIFE CYCLE (17-22 DAYS)

Pupa Egg (2-3 days) (10-12 days)

Adult Fig.2.4: Life Cycle of Uzi fly

z Adult uzi fly emerges from the pupa after 10 to 12 days.

z Life cycle is completed in 17-22 days.

z Adult fly survives for 10 - 18 days (males) and 18-22 days (females).

z Adult fly feeds on pollen, rotten fruits, nectar, etc. a) Period of occurrence

z In the southern sericultural belt (Karnataka, Andhra Pradesh and Tamil Nadu), the uzi fly is prevalent throughout the year. In other parts of the country, it does not prevail throughout the year because of discontinuous rearing of silkworm and environmental extremities.

z Maximum infestation is recorded during rainy season followed by winter.

z The infestation is least during summer months. b) Symptoms of attack and extent of damage

z The Uzi fly lays one or two cream coloured eggs (measuring the size of a pin head) on the silkworm larva. Generally, it prefers grown up larva (i.e., 4th or 5th instars) for egg laying (Fig.2.5 & 2.6).

z The eggs hatch in 48 to 62 hours. A black scar is formed at the point where the egg hatches and the uzi larva (maggot) enters the body of the silkworm using the hooks (pro-thoracic hook) attached to the mouth. From this black scar, the pest attack can be identified (Fig. 2.7, 2.8 & 2.9).

Fig.2.5: Adults of Uzi fly laying eggs on Fig.2.6: An Uzi egg on silkworm larva 24 silkworm larvae Silkworm Pests and their Management

Fig.2.7: Black Scar on silkworm larva Fig.2.8 : Uzi Maggot Fig.2.9: Uzi Pupa z The silkworm crop loss due to this fly pest is 10-20% i.e., on an average 6 kg reduction in cocoon yield is observed for every 100 dfls of silkworm reared. c) Factors responsible for outbreak of Uzifly

z Large scale and overlapping rearing of host (silkworm).

z Favourable climatic conditions (temperature range of 20 – 30°C and relative humidity of 60 – 90%) facilitates continuous host / silkworm rearing which in turn helps the host availability.

z Increased adult (uzi fly) longevity.

z Higher egg production and egg hatchability.

z Reduced activity of the natural enemies like parasitoids, predators and pathogens in nature.

2.4 UZI FLY MANAGEMENT AND ITS ECONOMICS i) Managment of Uzi fly

Various management methods have been evolved for the suppression of the uzi fly incidence. These are classified as –

z Cultural / Mechanical

z Exclusion

z Physical

z Chemical

z Biological

z Legislative/Quarantine a) Cultural / Mechanical

z Silkworm rearing in a village should be conducted at a time by all farmers.

z A minimum gap of 20 days should be maintained between the two silkworm rearings.

z The cracks and crevices on the rearing house floor must be kept closed.

z Collection and destruction of uzi infested silkworm larvae. 25 Silkworm Diseases and z Collection and destruction of uzi maggots and pupae from rearing house, Pest Management grainage, cocoon market and reeling establishment.

z Collection and destruction of adult uzi fly. b) Exclusion is by avoiding the contact of uzi fly with the silkworm.

z Use nylon net enclosure to the rearing stand (Fig.2.10).

z Fix wire mesh to windows and doors (Fig.2.11).

Fig. 2.10: Use of Nylon net Fig. 2.11: Fixing of Wire mesh

z Provide a small ante-room at the entrance of rearing house. Cover the individual rearing tray with nylon net. c) Physical

z Keep uzitrap solution in white trays near doors and windows (3 ft above ground level) both inside and outside the rearing house to trap adult uzi fly (Fig.2.12).

Fig. 2.12 : Uzitrap d) Chemical

z Spray / dust the ovicides like uzicide / uzipowder to kill the uzi eggs laid on silkworm body (Fig.2.13).

z Spray 2% bleaching powder solution on the body of silkworm larvae to detach / kill the uzi egg (Fig.2.14).

26 Silkworm Pests and their Management

Fig. 2.13: Spraying of uzicide Fig. 2.14: Dusting of uzipowder e) Biological control

z Release of Nesolynx thymus by keeping parasitised pupae ready for emergence on 2nd day after keeping packets (50 ml x 2 packets/100 dfls) on second day of fifth instar of silkworm rearing (Fig.2.15).

z Shifting of the parasitised pupa packets to places where mountages with silkworms are kept spinning (Fig.2.16).

Fig. 2.15: A pouch containing N.thymus, Fig. 2.16: An egg laying N. thymus adult parasitised host pupae f) Legislative / Quarantine z Avoid transportation of uzi infested cocoons from infested area to new area. The above management methods when applied individually do not keep the pest incidence below the economic injury level (5%). Hence, an Integrated Pest Management (IPM) package is developed for the suppression of the pest by selecting a few effective management strategies listed above. The IPM package for the control of uzi fly comprises Mechanical (use of nylon net enclosure), Physical (use of an adult trap – uzitrap), Chemical (spraying of uzicide or bleaching powder solution / dusting of uzi powder) and Biological (release of an ecto-pupal parasitoid, N. thymus) methods. ii) Economics (for 100 dfls silkworm rearing) A. Cost of the IPM package (per crop) Nylon net enclosure: Rs.200/- (durable for 5 crops) Rs. 40 Uzicide Rs. 60 Uzitrap Rs. 10 Bio-control agent (N. thymus) Rs. 20 Total Rs. 130 B. Cocoon yield loss/100 dfls 6 Kg = Rs. 720 @ Rs.120/Kg. C. Effectiveness of IPM package 84% D. Cocoon recovery due to IPM 5.04 Kg = Rs. 604.80 E. Net Profit = D - A = 604.8 – 130 = Rs. 474.80 Cost: Benefit ratio 1: 5.04 27 Silkworm Diseases and Pest Management 2.5 DERMESTES BEETLE

Dermestes Beetle: Dermestes spp. (Coleoptera: Dermestidae)

The most important species of dermestid beetle prevalent in egg production centers is Dermestes ater.

i) Identification of pest

z Adults of D.ater are black in colour, elongate oval in shape and about 7 mm in body length.

z Grubs (larvae) are also black in colour and are covered with bristles (‘hairs’) (Fig.2.17).

Fig.2.17: Dermestes beetle

ii) Life cycle

z The female lays 150-250 eggs in the floss of the cocoons.

z Egg hatching duration: 3-6 days.

z Larval (grub) duration (5-7 instars): 28-40 days.

z Pupal duration: 7-8 days.

z Total life cycle: 38-54 days.

iii) Period of Occurrence

z The pest prevails throughout the year.

iv) Symptoms of pest attack and extent of damage

z The grubs cause more damage than adults.

z The infested cocoons (especially seed and stifled cocoons) show the presence of multiple irregular holes on them.

z Though they show preference for feeding on the left over/dead matter in the cocoons, they do attack the green cocoons as well as the egg laying whenever their population gets increased (Fig.2.18).

z The estimated damage level due to the beetle attack to the pupae is 16.62% and moth 3.57% with 20.19% reduction in egg production in grainages, especially those coming under government sector. 28 Silkworm Pests and their Management

Fig. 2.18: Damage caused by dermestid beetles to the cocoons and egg laying silk moths v) Factors responsible for pest outbreak

z Storage of large quantities of moth pierced as well as stifled cocoons over a long period of time (more than 6 months). vi) Management a) Preventive measures

z Storage of rejected cocoons and perished eggs in the grainages for long period should be avoided.

z The cocoon storage rooms should be cleaned periodically.

z Before and after emergence of silk moth, the grainage premises should be kept clean and tidy.

z Provide wire mesh to doors and windows in Pierced Cocoon (PC) storage rooms to avoid free movement of the beetles and grubs from PC storage room to grainage operation rooms. b) Control measures 1) Mechanical

z Collect the grubs and adults either by sweeping or by using a vacuum cleaner and destroy them by burning or dipping in soap solution. 2) Physical

z Exposure of beetle infested (grubs and adults) pierced / stifled cocoons packed in HDPE (black) bags to sunlight for a period of 6 hours. 3) Chemical

z Wooden articles of the cocoon storage room and grainage should be dipped in 0.2% Malathion solution for 2-3 minutes. After 10 days, the trays should be thoroughly washed in water and sun dried for 2-3 days before reusing.

z Store pierced cocoons in Deltamethrin treated bags (bags soaked in 0.028% Deltamethrin solution and dried in shade).

z Spray 0.028% Deltamethrin solution on walls and floor of PC storage room once in 3 months. 29 Silkworm Diseases and z Sprinkle commercial grade bleaching powder @ 200 gm/m2 in the PC Pest Management storage room (close to wall) to prevent migration of grubs from PC storage room. vii) Economics of management A) Cost of the IPM package Mechanical Rs. 80 Chemical: Bleaching powder Rs. 100 Deltamethrin Rs. 250 Total Rs 430 B) Decline in egg production 5000 layings / lakh produced = Rs.12,500 @ Rs.250/100 dfls. C) Effectiveness of IPM package 90% D) Layings recovery due to IPM 4,500 = Rs. 11,250 E) Net Profit = C - A = 11,250 – 430 = Rs.10,820 Cost: Benefit ratio 1: 26

Check Your Progress 1 Note: a) Use the spaces given below for your answers. b) Check your answer with those given at the end of the unit. 1) What are the important pests of silkworm? ...... 2) What is the extent of damage caused by the important pests of silkworm? ...... 30 Silkworm Pests and 3) What are the symptoms of attack by the pests of silkworm? their Management ...... 4) How the important pests of silkworm are controlled? ...... 2.6 LET US SUM UP In this unit, you have understood two main insect pests, that causes damage to the silkworm as well as cocoons. The damage caused by them is considerable. The uzi fly can be controlled by following a few practices during rearing itself. However, the damage ranges from 10-20 % and sometimes the crop as a whole, as it continues the generations in the nearby vicinity of rearing. The dermestid causes considerable damage in the seed production. The important control measures explained comprises all possible methods which are economical and user-friendly as well as easy to implement, which ultimately reduce the income loss. 2.7 GLOSSARY Grainage : A place where silkworm eggs are produced. Grub : It is the immature stage in the life cycle of an insect belonging to the order Coleoptera. HDPE : High density polyethylene. Maggot : It is the immature stage in the life cycle of an insect belonging to the order Diptera. Parasitoid : It is an insect which multiplies on another insect (host) leading to the death of the host. Pierced cocoon (PC) : It is the cocoon resulted after the emergence of silk moth. Pupa : It is the quiescent (inactive) stage in the life cycle of an insect showing complete metamorphosis (change in the total appearance). Stifled cocoons : These are the cocoons subjected to hot air treatment to kill the pupae inside them. calculation : In order to prepare pesticide solution, the following formula can be adopted: a x b d = c 31 Silkworm Diseases and Where, Pest Management d = Quantity of the commercial formulation required. a = Concentration (%) of the pesticide. b = Quantity of solution/dust required. c = Concentration (%) of the active ingredient in the commercial pesticide. 2.8 SUGGESTED FURTHER READING Anonymous. 1975. Textbook of Tropical Sericulture. Overseas Co- operation Volunteers, Tokyo. pp. 594. Anonymous. 1976. Report of the National Commission on Part IV. Climate and Agriculture. Govt. of , Min. of Agriculture and Irrigation, New Delhi. pp. 638. Anonymous, 1982. Studies on the sterile technique to control Exorista sorbillans on . Yuanzineng Nangye Yingyang, 2L: 11-16. Channabasavanna, G.P., Siddappaji, C. and Dandin, S.B. 1993. Integrated management of Indian Uzi fly, Exorista bombycis infesting the mulberry silkworm. Rec. Adv. Uzi Fly Res., Proc. Natl. Sem. Uzi fly and its control, KSSRDI, Bangalore, pp.229 – 237. Datta, R.K. and Mukherjee, P.K. 1978. Life history of Tricholyga bombycis, (Diptera: Tachinidae) a parasite of Bombyx mori (Lepidoptera: Bombicidae). Ann. Entomol. Soc.Am. 71:767-70 Jolly, M.S., Baig, M. and Chandrashekaraiah. 1982. Silkworm rearing under nylon net - a short term control measure evolved by CSRTI, Mysore. Workshop on Uzi Fly Control, CSRTI, Mysore, pp. 7 – 8. Jolly, M.S. and Kumar, P. 1985. A three pronged approach to control Uzi fly. Indian Silk. 23 (10 & 11): 5 – 11. Krishnaswami, S., Jolly, M.S. and Datta, R.K. 1964. A study on the fly pest infestation of the larvae and cocoons of Bombyx mori L., Indian J. Seric. 3: 7-12. Kumar, P. 1987. Contribution to our knowledge on Tricholyga bombycis, a serious parasite of Bombyx mori and its control. Ph.D. Thesis, Mysore University, Mysore, pp. 328. Kumar, P. and Jolly, M.S. 1986. Efficacy of nylon net enclosure in containing Uzi fly (Tricholyga bombycis) infestation to silkworm (Bombyx mori L.). Indian J. Seric. 25: 74 – 77. 2.9 REFERENCES Jolly, M.S. 1981. Uzi fly - Its identification, prevention and control. CSRTI, Mysore, Bull.No. 4, pp.8 Jolly, M.S. 1982. Uzi fly incidence and its preventive measures. Reshme Krishi, 4(1): 27 – 32. Krishnaswami, S., Narasimhanna, M.N., Suryanarayana, S.K. and Kamaraj, S. 1973. Manual on Sericulture: Silkworm Rearing. FAO, Rome. pp.131. 32 Silkworm Pests and 2.10 ANSWERS TO CHECK YOUR PROGRESS their Management

1) The uzi fly, Exorista bombycis during silkworm rearing and Dermestid beetles (Dermestes spp.) during cocoon stage are the important pests of silkworm. 2) Uzi fly causes 10 – 20% reduction in cocoon yield (6 Kg/100 dfls). Dermestid beetles cause 20.19% reduction in silkworm egg production. The dermestid beetles attack the pierced cocoons and stifled cocoons and damage the silk content thus lowering the quality of the silk produced. 3) Presence of black scar on the silkworm body and a circular hole at the tip of the cocoon are the typical symptoms of uzi fly attack. Presence of multiple and irregular shaped holes on the cocoons, damaged abdomen in silk moths are the symptoms of dermestid beetle attack. 4) The uzi fly is effectively controlled using cultural/mechanical, exclusion, physical, chemical, legislative and biological methods. The dermestid beetles are controlled by physical as well as chemical measures apart from a number of preventive measures.

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