Epizootics of entomopathogenic fungi, Beauveria bassiana (Balsamo) on the zoophytophagous mirid bug, Nesidiocoris tenuis (Reuter)

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1 Epizootics of entomopathogenic fungi, Beauveria bassiana (Balsamo) on the zoophytophagous mirid bug, Nesidiocoris tenuis (Reuter) S. Onkara Naik, M. Jayashankar, V. Sridhar and A. K. Chakravarthy* Division of Entomology and Nematology, Indian Institute of Horticultural Research, Hessaraghatta Lake Post, Bengaluru , Karnataka, India * Studies of infection of mycoinsecticides have concentrated on insect pest management. However, data on their impact on predatory bugs are meagre. The present study focuses natural incidence of Beauveria bassiana (Balsamo) Vuillemin (Ascomycota: Hypocreales) on the mirid bug Nesidiocoris tenuis (Reuter) (Heteroptera: Miridae) from India. N.tenuis is a generalist predator of Bemisia tabaci (Gennadius), Tetranychus urticae (Koch), Spodoptera litura (Fab.), Ephestia kuehniella (Zeller) and Tuta absoluta (Meyrick) in agri-horticultural ecosystems (Patel, 1980; Raman and Sanjayan, 1984; Sancheza and Lacasa, 2008; Urbaneja et al., 2005; Perdikis et al., 2009; Hughes et al., 2009). While ubiquitous entomopathogenic fungus, B.bassiana has been examined for biological control against many insect pests, many formulations have been developed with variable success in pest management (Boyle and Cutler, 2012; Chandler et al.2011; Lacey et al. 2001). It is natural epizootics in select, cultivated ecosystems (Luan, 2011). Occurrence of B.bassiana on the natural population of N.tenuis on tomato cultivated in open and polyhouse conditions is presented here. Table 1: Insect hosts of B.bassiana in agro-horticultural ecosystems of India Sl. Insect hosts No. 1 Lachnosterna (=Holotrichia) consanguinea 2 Phytoscaphus sp., larval stages of Chilo auricilus, C.infuscatellus and Sesamia inferens, Nymph and adult of Cavelerius sweeti and adult of Astychus lateralis. 3 Mylloceros viridianus and Calopepla leayana Crop/Laborator Reference y condition and location Sugarcane, Bihar Rao and Vijayalakshmi Sugarcane, Uttar Pradesh (1959) Varma et al., (1988) Teak, Kerala Sankaran et al., (1989) 4 Sahyadrassus malabaricus Saplings, Kerala Ali and Mathew, (1989) 418

2 5 Spodoptera litura (used in Laboratory Rao et al., (2005) combination with Nomuraea rileyi) conditions 6 Psychids (bagworms), leaf web worms Oil palm, Andhra Pinnamaneni and Kalidas, and slug caterpillars Pradesh (2010) 7 Helicoverpa armigera larvae Laboratory Tyagi et al., (2010) conditions 8 Basilepta subcostatum Banana Choudhary et al., (2010) 9 Eutectona machaeralis Teak, Karnataka Patel and Thontadarya, (1981) Weekly observations to record insect pests and their natural enemies was undertaken on two tomato varieties viz, Arka Rakshak and Arka Sourabh were cultivated during rabi 2012 and kharif 2013 under open and protected cultivation at the Indian Institute of Horticultural Research (N '05'' E '53'', altitude 2853 ft), Hessaraghatta, Bangalore. Simultaneous surveillance was undertaken in polyhouse with tomato cv. Arka Rakshak and adjacent open field condition with cv. Arka Sourabh. Visual observation during weekly monitoring of tomato crops under polyhouse and field conditions revealed N.tenuis cadavers on the leaves. Subsequently the sporulated cadavers were carefully collected and carried to laboratory for taxonomic identification. On confirming the fungal pathogen, further studies were designed for both the fields. Spores collected from the fungus infected cadavers were cultured to isolate a pure strain using potato dextrose agar medium. The spore morphological features agreed with those described from B.bassiana. The samples were recorded at weekly intervals and the observations were carried out on 15 randomly selected tomato plants during meteorological weeks 48 (2012) 6 (2013). The observations were replicated six times. Different life stages of the bug including 1 st -5 th instars and adults containing conidiophores were manually counted on the plants. The weather data were obtained from the IIHR meteorological observatory to perform correlation analysis to establish any relationship between abiotic factors and the incidence of B.bassiana on N. tenuis. Temperature and humidity data were recorded separately within the polyhouse using a thermohygrometer, 4 times a day, morning, forenoon, mid noon and dusk during the period of observation. Statistical analyses were performed using SPSS (11.0 version) to analyze the mean percent mortality and correlation between percent mortality with abiotic factors. Evidence of infected cadavers of N. tenuis was found covered with conidiophores during the present observations thereby confirming the incidence of entomopathogenic fungi B.bassiana on N.tenuis both under polyhouse and open field conditions on two, test varieties of tomato (Figs. 1-2). The mean percent mortality under polyhouse condition was ± % ranging between to 80% within the replicates. Percent mortality showed a positive 419

3 correlation with average temperature (0.114) and negative correlation with average humidity (-0.50) (Fig.4). The mean percent mortality under field condition was ± % ranging between to 60% within the replicates. Percent mortality showed a positive correlation with average humidity (0.31) and negative correlation with average temperature (-0.09) (Fig.5). The fungal infection was observed on all stages of the insect. The incidence was marginally higer under open field conditions compared to polyhouse conditions. Based on the present study, it could be inferred that the fungus could provide sufficient protection against outbreaks of N.tenuis when it becomes phytophagous incurring damage to cultivated crops (Sridhar et al., 2012). The present observations were available for N.tenuis as host, warranting more observations as the fungus may affect a number of economically relevant species, both pest and beneficial in the study region. Populations of B. bassiana are densitydependent mortality factors in susceptible host populations and successful infection depends on the host receiving a threshold of infective conidia (Vandenburg et al., 1998; Hughes et al., 2004). CONCLUSION: The present observations are first time record of Beauveria bassiana (Balsamo) incidence on Nesidiocoris tenuis from India. The mean percent mortality of bug predator ranged from % under polyhouse conditions and to 60% under field conditions. Acknowledgements: We thank Director, Indian Institute of Horticultural Research (IIHR) for encouragement and providing us with the facilities. Fig. 1. Nesidicoris tenuis a) Healthy b) Naturally infected by B.bassiana Fig. 2. Completely encapsulated cadavers of N. tenuis 420

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