Diversity of bees in two crops in an agroforestry ecosystem in Kangsabati South Forest

: The investigation study assesses the diversity of bees in Brinjal

ISSN 0974-7907 (Online); ISSN 0974-7893 (Print) Now-a-days, agroforestry is an important ecosystem especially in a tropical country and it is an intensive land management system. It consists of agriculture systems and have potential biodiversity conservation sites. The agroforestry ecosystem provide rural livelihood alongside biodiversity conservation in a sustainable land use system. This system is a transitional process from conventional agricultural practices to agro-ecological agricultural practices (Souza et al. 2014). Combination of crops and diverse plants species in forest provide a rich insect diversity due to increased niche diversity than any agro-ecosystems (Stamps & Linit 1998). Heterogeneous agroforestry ecosystem provides floral resources for pollinators (Sinu & Shivanna 2007). Habitat loss and intensification of agricultural practices threaten wild as well as domestic pollinators. Agroforestry ecosystem provides them suitable nesting sites and floral resources, enhancing their pollination services to crops at a landscape level (Sutter 2017;Kay et al. 2019). Bees are the primary pollinators and roughly cover 90% of world plant population (Winfree 2010).
In agriculture land bees are the essential pollinators for pollination as well as crop production. Non Apis species are effective pollinators than honey bees (Javorek 2002;Kreman et al. 2002), but they both can together enhance crop production (Greenleaf & Kreman 2006). Brinjal Solanum melongena L. and Ridge Gourd Luffa acutangula L. are important and widely cultivated crops across the studied area and also bee-attracting vegetable crops. Buzz pollinators are effective pollinators for solanaceous (Brinjal) and cucurbitaceous (ridge gourd) crops. Brinjal flowers have abundance of pollen but to expel the pollen requires vibration by insects called 'buzz pollination'. Wild bees are efficient in buzz pollination than honey bees (Buchmann 1983;Herren & Ochieng 2008). Natural forest is a suitable habitat for wild bees but due to extensive deforestation they are in threat. This investigation was carried out to generate information about the diversity of bees in pollination dependent crops in an agroforestry ecosystem.

Study Area
The study was conducted in an agroforestry ecosystem in western part of West Bengal, India. The studied area is in Kangsabati South Forest Division in Purulia. The forest division is situated between 23. 166-22.833 N & 86.666-87.000 E, covering 310.27 km 2 areas, which are continuations of the Chotanagpur Plateau ( Figure 1). Mixed cropping system is practiced dominantly in the studied area. Fourteen plots were selected randomly throughout the South Kangsabati Forest Division on the basis of easy accessibility and densely blooming flowering plots. These fourteen plots were equally divided into seven plots for each crop. The experimental study was conducted in various farm lands from May 2021 to May 2022 in the eggplant and ridge gourd crops fields.

Methods
All bee surveys were conducting from 0830 h to 1630 h, split in three time hours: 0830-0930 h, 1130-1230 h, & 1530-1630 h. Bees are active in warm, sunny days so rainy and cloudy days were avoided for the unbiased data. Three methods-transect, focal observation (15 mins), and pan traps (yellow, white, blue colored pan traps)-were followed throughout one year of survey. The transect length was 100 m with 2-m breadth on each side (Sutherland 1996). In focal observation (Gibson et al. 2011), a 1 m 2 flowering plot was selected randomly and bees were observed for 15 mins. Pan traps of three different color sets were used for passive sampling (Westphal et al. 2008). Yellow, white, blue pan traps were used which were painted with UV-bright colors. Five clusters of pan traps were installed where each cluster was separated from another by a distance of 15 m. Each cluster contained three sets of pan traps filled with 400 ml soapy water. The species not identified in the field were collected through sweep net, killed by ethyl acetate, and preserved in 70% ethanol for future reference. We followed Bingham (1897) and Michener (1974Michener ( , 1994Michener ( , 2007 for bee identification. We observed diversity and abundance of bees by observing bees visiting Brinjal and Ridge Gourd flowers. These data were used for analyzing bee diversity by Shannon diversity index (H') and Shannon evenness index (J'). The number of bees data (sampled via transect, focal observation & pan trap) were pooled in each crop independently for analysis of richness and abundance. The data were analyzed using Past Software 3.4. Shannon Diversity Index (H') = -Σp i * ln(p i ) Shannon evenness index (J ) = H/lnS Relative Abundance= (N i /N)*100 Where, S is the total number of species and p i is the proportion of the entire community made up of species i. N i is the abundance of species i and N is the total of all species encountered.

Results and Discussion
A total of 1,085 bee individuals were encountered belonging to three families (Apidae, Halictidae, Megachilidae), seven genera and 17 species during the survey. Tetragonula iridipennis was most dominant species with 262 individuals followed by Apis florea (182 individuals) and Nomia elliotii (169 individuals). Most of the bee species belonging to the family Apidae were observed during the study. During the survey time, non Apis bees (63.78%) were dominant in abundance than Apis bees (36.22%).
In the Ridge Gourd, the Shannon diversity index was 1.94 and Shannon evenness index was 0.3, Apis florea was the most abundant species with 23.48%, followed by Apis dorsata (21.25%) and Tetragonula iridipennis (17.83%). Amegilla zonata (0.74%) and Megachile lanata (0.3%) were rare visitors of ridge gourd flower. Apis bees were the most dominant visitors of ridge gourd flower followed by Nomia elliotii of Halictidae family, bees from subfamily Xylocopinae (Xylocopa & Ceratina bees) were frequently observed from Apidae family. Among wild bees, Xylocopa fenestrata and Nomia elliotii were dominant throughout the survey in both the crops. Patricio et al. (2012) recorded the role of bees as Agroforestry not only provides niche diversity, it also reduces pest problems (Stamps & Linit 1998).

Conclusion
The experimental study proves that there is a great diversity and abundance of non Apis bee species along with Apis bee species present in Brinjal and Ridge Gourd fields, as surrounding natural habitat provide them alternative habitat and floral resources which enhance the diversity and population of wild bees.

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