Tropical Tasar culture is forest and agro-based activity that covers agricultural and industrial activity. Tasar silk is produced by “Antheraea mylitta” which is polyphagous in nature. Its primary food plants are “Terminalia arjuna” and “Terminalia tomentosa” commonly known as Arjun and Asan, respectively. A large number of pests are reported to attack both the host plants as well as silkworm. Earlier natural forest grown plants were used for silkworms rearing. But adaptation of scientific farm techniques in cultivation of food plants lead to intensive cultivation of food plants in huge acreage which resulted in monoculture of host plants. Thereby the incidence of pest attack to host plants and silkworm has been increased.
Tasar silkworm, Antheraea mylitta belongs to Order-Lepidoptera. The life cycle of silkworm consists of Egg, Larva, Pupa and Adult stages. As the rearing is conducted outdoor silkworms are exposed to attack of various pests during their life cycle. The estimated crop loss due to pests is to the tune of 40 - 45%. Vapourer tussock moths are major pests of primary tasar food plants Terminalia arjuna Bedd and Terminalia tomentosa W & A and cause considerable damage. The young larvae nibble on the leaf surface while older larvae consume whole leaf.
The pests of tasar silkworm are broadly categories into predators and parasitoids. Predators cause damage to tasar larvae during early instars and parasitoids during later stages. Due to these pests the production of tasar silk is affected considerably. The major parasitoids and predators of silkworms are Uzi fly (Blepharipa zebina) and Ichneumon fly (Xanthopimpla pedator), Stink bug (Eocanthecona furcellata), Assassin bug (Sycanus collaris) Praying mantis (Hierodulla bipapilla), Wasp (Vespa orientalis) and Red ant (Oecophylla smaragdina).
Among the predators of silkworm the stink bug, Eocanthecona furcellata is very serious predator which attack the silkworm during young age rearing. The prevalence was more during II and III crop rearing than in I crop rearing season. It survives on other hosts during non-rearing season. Some of the pests/herbivoures of tasar host plant like larvae of vapourer tussock moths, semilooper, leaf hopper nymphs and boll headed caterpillar, etc., serve as alternate (secondary) hosts to E. furcellata. The present study was undertaken to study the life cycle of E. furcellata on vapourer tussock moth larvae.
The adults of Eocanthecona furcellata were collected from the rearing field of CTR&TI, Ranchi. They were maintained in the laboratory on silkworm larvae to get the eggs for the experiment. Stock culture of the stink bug was maintained on silkworm larvae.
The larvae of vapourer tussock moth were collected from the rearing field of CTR&TI, Ranchi and the culture was maintained in the laboratory in perforated plastic boxes on leaves of Terminalia arjuna.
The eggs of E. furcellata were taken from the stock culture maintained in the laboratory to study the life cycle on vapourer tussock moth larvae. The eggs were incubated at room temperature. After hatching 5 newly hatched nymphs were transferred in to a plastic box. The lid of the box was covered with muslin cloth to facilitate aeration. Five first instar larvae of vapourer tussock moth along with the leaves of T. arjuna were provided as food for the newly hatched stink bug nymphs. T. arjuna leaves served as food for vapourer tussock moth larvae. Mortality of the vapourer tussock moth larvae was recorded daily. The feeding was provided daily. First to third instar vapourer tussock moth larvae were provided as food for I - III instar nymphs of stink bug. Fourth and fifth instar nymphs and adult stink bugs were provided IV and V instar vapourer tussock moth larvae as food. Five replications were maintained. In control, first to third instar silkworm larvae were provided as food. The parameters like incubation period, number of instars, duration of instars, mating, pre-ovipositon, oviposition, fecundity, and longevity of adult stink bugs were recorded.
Seven types of vapourer tussock moth larvae were collected from the field. The species which was abundant was used in the study.
Different species of Vapourer tussock moth larvae infesting tasar host plants
The incubation period of stink bug eggs varied from 7-9 d with an average of 8.00 ± 0.45 d. The eggs were silver coloured when laid and turned to reddish brown 24 – 48 h before hatching.
The nymphs emerged from the dorsal surface of eggs by removing the upper lid. The first instar nymphs were reddish with yellow colour which later turned slowly into black and red. They were gregarious and found to feed on sap of tender leaves of T. arjuna. They had three pairs of legs. The first instar lasted for 2-3 d with an average of 2.60 ± 0.25 d. The first moulting period 01 d. Second instar nymphs were light red in colour, gregarious in nature and fed on second and third instars of vapourer tussock moth larvae. Second nymphal instar duration varied from 2-4 d with an average of 3.00 ± 0.32 d. Second moulting duration was 01 d. Third instar nymphs were bigger in size, dark reddish in colour and gregarious in nature. They fed on second and third instars larvae of vapourer tussock moth. The third instar duration ranged from 3-5 d with an average of 4.00 ± 0.58 d. The third moulting duration lasted for 01 d. The newly moulted out fourth instars nymphs were light red in colour initially and later turned to dark red colour with yellow patches. The fourth instar nymphs were solitary in nature and found to feed on third and fourth instar larvae of vapourer tussock moth. The instar duration was 4.00 ± 0.32 d with a range of 3-5 d. Duration of fourth moult was 01 d. The newly moulted out fifth instar nymphs were dark black in colour and solitary in nature. They preyed upon third – fifth instar larvae of vapourer tussock moth. They had longer nymphal duration than other instar nymphs, which ranged from 4-6 d with an average of 5.60 ± 0.50 d.
After completion of fifth nymphal instar the nymphs shed their last nymphal skin and emerge as adults. The newly emerged young adults were red in colour and later on changed to dark brown. Males were smaller and more active than females. Total developmental period of E. furcellata from egg to adult when cultured on vapourer tussock moth larvae was 22.00 ± 4.20 d.
After emergence as adult they did not copulate immediately. The pre-copulation period fluctuated from 4-5 d. Average pre-copulation period was 4.60 ± 0.25d. In captivity, copulation period ranged from 16-36 h with an average of 25.60 ± 3.77 h. During copulation both the sexes remained stationary in opposite direction in end to end position.
Female stink bug oviposited after 3-4 d of copulation. The average pre-oviposition duration was 3.20 ± 0.38 d. The eggs were laid in small clutches arranged in 4-8 rows. In laboratory condition the eggs were laid on leaves, walls of the culture jar and cloth used to cover the jars and blotting paper. The average number of eggs/clutch was 30.14 ± 3.41 (range 24-60). The fecundity of a single female varied from 210-405 eggs with an average of 302.54 ± 37.27.
In laboratory the longevity of males and females ranged from 29 - 45 d and 30 - 48 d with an average of 37.00 ± 3.18 and 42.40 ± 1.94 d, respectively.
In control where the silkworm larvae were used as food for E. fucellata the nymphal duration ranged from 2 - 3, 2 - 3, 3 - 4, 3 - 5 and 4 - 6 d with an average of 2.20 ± 0.20, 2.60 ± 0.25, 3.50 ± 0.29, 3.60 ± 0.40, & 4.80 ± 0.38 d respectively in first, second, third, fourth and fifth instar. The pre-copulation, copulation, pre-oviposition and oviposition period was 4.20 ± 0.20, 18.20 ± 2.87, 3.40 ± 0.50, and 20.20 ± 1.07 d, respectively. Total developmental duration of E. furcellata from egg to adult ranged from 20.00 ± 4.42 d when provided silkworm larvae.
Eocanthecona furcellata is being used as a biocontrol agent in agriculture and forest plantation. It is an important predator of several economically important forest plant pest. There are reports on its predation on poplar defoliator, Closter Spp. (Sangha and Sohi, 2008, Ahmad et al., 1996, Ganguli et al., 2000), Helicoverpa armigera and Leucinodes orbonalis (Aganon et al., 2008), Spodoptera litura (Yasuda and Wakamura, 1996), and Corcyra cephalonica (Kumar et al., 2007).
The incubation period of E. furcellata in our study is in agreement with the reports of Ray and Khan (2011) and Kumar et al., (2007) who reported incubation period of E. furcellata as 7 – 9 d and 8.25 d when cultured on Clostera fulgurita and Corcyra cephalonica, respectively. However our results are in contrast with the reports of Ahmad et al., (1996) who observed 4 – 8 d of incubation period of E. furcellata when cultured on Clostera cupreata. The difference in incubation period may be attributed to seasonal variation which leads to fluctuation in temperature and humidity.
The results of Ray and Khan (2011) regarding nymphal instars, nymphal duration of E. furcellata when reared on C. fulgurita is in consonance with our findings. The author reported nymphal duration of I – V instar respectively as 2 - 3 d, 2 - 3 d, 2 - 3 d, 2 - 3 d and 4 - 6 d. Ahmad et al., who reported the fifth instar nymphal duration range from 2 – 5 d is more or less similar to the present report. Ray and khan (2011) reported that the total nymphal duration of E. furcellata ranged from 13 – 16 d with an average of 14.1 d. In the present study the average nymphal duration was 16.00 ± 3.24 d which more or less fall in line with the reports of Ray and Khan (2011). The results are also in accordance with the results of Kumar et al., (2007) who reported 12 – 17 d of total nymphal duration with an average of 14.50 d.
Ray and Khan (2011) reported that the young adults were yellowish in colour and later on changed to dark brown which is contrast to our results where the colour of newly emerged young adults were red in colour and later on turned to dark brown.
Kumar et al., (2007) recorded pre-copulation and copulation periods of E. furcellata when reared on C. cephalonica as 6 d and 11.35 h. Ray and Khan (2011) reported 4.9 d of pre-copulation 12.40 h of copulation period. The present results of pre-copulation period are in agreement with the reports the above authors. However, the copulation duration was in contrast with the above observations. The reason for increased copulation duration in the present study may be attributed to low temperature in the month of December.
Ray and Khan (2011) and Kumar et al., (2007) recorded the life time fecundity of a single female as 317.6 and 241.62 eggs. Fecundity recorded in the present study is in accordance with the reports of Ray and Khan and in disagreement with the result of Kumar et al.
The longevity of stink bug male and female was reported as 16.8 and 24.7 d, respectively by Ray and Khan (2011) is not in agreement with our results.
The vapourer tussock moth which served as host for E. furcellata is one of the major defoliators of the tasar food plants. Apart from vapourer tussock moth other major/minor pests of tasar host plants viz., larvae of vapourer tussock moth, nymphs of leaf hopper, different species of semilooper, boll headed caterpillar are also serve as alternate hosts for E. fucellata during non-rearing season where silkworm larvae are not available in the field. After completion of rearing there is no practice of management methods to control the tasar host plant pests. This situation leads to population build up of E. furcellata which multiply on several alternate/secondary hosts. To check the multiplication of silkworm predator, E. furcellata adoption of pest control measures for defoliators of tasar host plants during non-rearing periods is necessary.