Introduction

Tea is a perennial crop and grown as a monoculture over large contiguous areas during last 160 years had formed a stable tea ecosystem for widely divergent endemic or introduced pests. Each tea growing country has its own distinctive pests, diseases and weeds. 1034 species of arthropods and 82 species of nematodes are associated with tea plants (Chen and Chen, 1989). Among them, 25 species of insects, 4 species of mites and 10 species of nematodes are recorded from Bangladesh (Ahmed, 2005). Only few of them have become major pests while most of them are minor and localized and cause occasional damage. About 15% of its crop could be lost per year by various pests particularly insects, mites and nematodes if adequate control measures are not taken (Ahmed, 1996). Moreover crop losses to the extent of 50% or more may be inflicted by the advent of an epidemic or outbreak of specific pests in a particular season or tea estate.

Termite is a major serious pest of tea plantation in Bangladesh. It is a rather persistent and permanent pest of tea. Termites abound throughout the tropics and also occur in most warm and temperate countries in the world. They extend to about 45°N to 50°N (Metcalf, 1951; Emersion, 1955; Haris, 1961 and Araujo, 1970). It normally attacks the old tea bushes as well as young tea of new plantations. They feed on dead bark, rotten and live wood of tea plants. They live on colonies making mounds in the soil or stumps of plants (Ahmed, 1997). Many termite species are responsible for considerable damage to tea bushes and shade trees. Among the termite castes, worker caste is very dangerous to tea. Termites that are responsible for damage to tea bushes may be classified into two groups: live wood termites and scavenging termites. Live wood termites attack living tissues of tea bushes and are considered to be primary pests of tea. They excavate galleries within the live wood of wood of healthy tea plants. Tea plantation of Bangladesh is primarily invaded by four species of live wood termite, namely Coptotermes heimi Wasmann of Rhinotermitidae family; Microcerotermes championi Snyder, Microtermes obesi Holmgren and Macrotermes aleemi Holmgren of Termitidae family. Scavenging termites attack dead and dying tissues and are regarded as secondary pests of tea. There are three species of scavenger termites, namely Odontotermes feae Wasmann and Odontotermes horni Wasmann and Odontotermes parvidens Holmgren and Holmgren (Ahmed, 2005).

Several strategies were adopted to control this notorious malady. Chemical control is one of the important and fast action approaches in controlling termites in tea. Termiticides, such as Chlorpyrifos, Imidacloprid, Fipronil, Thiamethoxam groups are recommended for the control of termite pest of tea in Bangladesh (Mamun et al., 2014). The large-scale use of synthetic insecticides leads to adverse effects such as development of pesticide resistance, frequent pest out breaks, emergence of new pests, pollution and health hazards. In order to search an environmentally safe alternative, scientists considered the pesticides of biological origin in the place of synthetic insecticides. Replacement of synthetic insecticides by bio-rational insecticide is a universally acceptable and practicable approach worldwide (Rathi and Gopalakrishnan, 2006).

In this context, biopesticides are being considered as environmentally safe, selective, biodegradable, economical and renewable alternatives for use in Integrated Pest Management programme in tea. No bio-pesticide is available in Bangladesh at this moment. For this, an attempt was made by using an entomophathogenic fungus, Metarhizium anisopliae (Bioterminator) for the control of termites in tea. Bioterminator is Kaolin based formulation of Metarhizium anisopliae. Bioterminator is Kaolin based formulation of Metarhizium anisopliae. Bioterminator contains the insect pathogenic fungus, Metarhizium anisopliae, which is a widely distributed soil-inhabiting fungus. When sprayed on the plant, it generally enters into the insects through spiracles and pores in the sense organs and kills the insects. It can penetrate the body of the insect and kills it by secreting a toxin called DESTRUXIN (Plate 1). It does not leave harmful residues; environmental friendly and have no adverse effect on soil or plants or humans or animals. Therefore, an experiment was conducted to evaluate bioefficacy of Bioterminator, Metarhizium anisoplae against termite in tea.

1 Materials and Methods

1.1 Laboratory bioassay

A laboratory bioassay of Metarhizium anisopliae against termites was conducted at Entomology laboratory, Bangladesh Tea Research Institute, Srimangal, Moulvibazar. The product is supplied by Shakti Biotech. Ltd., India. Three different components such as Metarhizium anisopliae @ 5.0 g/L, Imidacloprid @ 1.5 ml/L and Chlorpyrifos @ 10ml/L water were used in this experiment and considered as treatments. Only water solvent was used in the control. Each treatment was replicated for three times. The fungus was formulated into a wettable powder form at the concentration of 2 x 10⁸ conidia g^-1 (Table 1). The infectivity of the isolate was evaluated by directly applying conidial suspensions @ 5.0 g/L water to individual termite workers by microapplicator. Termite workers were placed separately in Petri dishes (Plate 1). The Petri dishes were covered and then placed over ice to lower termite activity. The mortality was recorded daily upto 7 days after treatment (DAT). At each observation, dead termites were counted and removed from the Petri dishes. At each observation, dead termites were removed, counted and placed in dishes (90 × 15 mm) lined with wet filter paper and maintained at 25°C in growth chamber for mummification and sporulation to prove that the insects died because of the fungi used. Mortality data were corrected by Abbott’s (1925) formula.

Note: P = Corrected mortality (%); P´= Observed mortality (%); C = Control mortality (%).

1.2 Field experiment

An experiment was carried out to determine the bioefficacy of Metarhizium anisopliae (Bioterminator) against termites infesting tea at the main farm of Bangladesh Tea Research Institute, Phulbari Tea Estate, Baraoora Tea Estate, Srimangal, Moulvibazar, Bangladesh during February 2015 to October 2015. The experiment was designed with RCBD in the field.  Bioterminator (Metarhizium anisopliae) which is an entomopathogenic fungus and this product was compared with two commonly used synthetic pesticides i.e. Organophosphate chemical Chlorpyrifos (Dursban 20EC) and Neonicotinoid chemical Imidacloprid (Admire 200SL) as standard because Bioterminator is the only bio-pesticide in Bangladesh tea. Three trials were done in three different locations for confirmation of the efficacy (Table 2). Each treatment was replicated thrice in every location. Irrigation was done before application of M. anisopliae to keep the soil moistened. Five gram (5.0 g) of Bioterminator powder was added per liter of water. Forking was made as a prerequisite to achieve good results. Drenching was done around the bush near the collar zone. Rotten cow dung @ 300 kg and 3.0 kg M. anisopliae were mixed together and kept it for 3-7 days in shade. 2.0 kg molasses was also added to it. The mixture was applied around the collar region of the bushes. After that proper mulching was done to protect the microbes from direct sun accordingly. All the bushes in each plot were checked thoroughly and percent of termite infestation recorded before initial application (Plate 1). Post-treatment observations were noted regularly at monthly intervals. A total of nine observations were recorded up to 9 months after application. For determination of the effectiveness of the product, data was analyzed using Henderson and Tilton’s (1955) formula.

Note: cb = No. of insect population in control before treatment;

ca = No. of insect population in control after treatment;

tb = No. of insect population in treated before treatment;

ta = No. of insect population in treated after treatment.

1.3 Statistical analysis

The experimental data were statistically analysed by Completely Randomized Design (factorial CRD) and Randomized Complete Block Design (RCBD) using MSTAT statistical software in a microcomputer. The data were statistically analyzed by one-way ANOVA, with the level of significance set at p<0.05. The mean values were separated by Duncan’s Multiple Range Test (DMRT).

2 Results and Discussion

2.1 Laboratory experiment

Result revealed from the laboratory bioassay that Bioterminator was found to be effective (43.28-72.94) for controlling termites up to 7 days after treatment. The average mortality rate of termite was found 56.83% due to application of Bioterminator (Table 3). The rate of mortality of termites increases with the increases of time. The significant difference was found in the different treatments used in the experiment.

2.2Field experiment

The results achieved from the three trials at different locations are presented in the following tables (Tables 4, 5 and 6). Result revealed that Bioterminator was found to be highly effective (85.21, 84.91 and 85.97%) in controlling termites ate BTRI main farm, Phulbari Tea Estate and Baraoora Tea Estate, respectively (Figure 1). Effectiveness of the tested biopesticide was maintained the desired level up to 9 months. The significant differences were found in the different treatments used in the experiment.

Hussain et al. (2011) found that the M. anisopliae has pronounced positive effect in the control of termites at the time of sugarcane planting by increasing germination and reducing sugarcane bud damage. Singha et al. (2011) found that the strains of Metarhizium anisopliae (Metschnikoff) Sorokin and the strains of Beauveria bassiana (Ballsamo) Vuillemin effective agents against tea termite, Microtermes obesi Holmgren. In general, the M. anisopliae strains were more virulent with lower LT₅₀ values than B. bassiana strains. The LT₅₀ values ranged from 1.6 to 3.7 days. The M. anisopliae strains had low LC₅₀ values compared to B. bassiana strains. The LC₅₀ values ranged from 35 to 140 conidia per termite. Field applications of the isolates also produced promising results. Mohammadbeigi and Port (2013) studied on the pathogenicity of the fungi Beauveria bassiana and Metarhizium anisopliae against the long-horned grasshopper Uvarovistia zebra and found effective for M. anisopliae caused 100% and 53.3% mortality, respectively when they were sprayed onto the nymphs. Both species of fungi caused significant mortality of U. zebra by both contact and ingestion. Debnath et al. (2012) also found very effective using Metarhizium anisopliae for the control of live wood termites infesting tea in Cachar. The above findings achieved by different authors support the present experiment using M. anisopliae for the control of termites infesting tea in Bangladesh.

3 Conclusion

From the overall performance of the tested Bioterminator against termites of tea in Bangladesh was found effective in both laboratory and field condition. Hence, the Bioterminator may be efficiently used for the management of termites in tea as the component of IPM and reduce load of synthetic chemicals on tea.

Acknowledgement

The authors are very much grateful to Dr. Mainuddin Ahmed, Director, Bangladesh Tea Research Institute, Mr. Md. Khalilur Rahman, General Manager, Phulbari Tea Estate, M. Ahmed Tea & Lands Company Ltd. and Mr. G.M. Shiblee, Deputy General Manager, Baraoora Tea Estate, Finlays for their kind cooperation during the study as a part of the PhD research work of the first author.

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