Parthiba Basu

Pesticide-induced oxidative stress in laboratory and field populations of native honey bees along intensive agricultural landscapes in two Eastern Indian states

Pesticides have been cited as one of the major drivers of pollinator loss. However, little is known about pesticide impacts on natural populations of native honey bee species. This study looked into the effect of pesticides with respect to oxidative stress in the laboratory and in field populations of two native Indian honey bee species (Apis dorsata and A. cerana) by examining a combination of biomarkers, e.g., superoxide dismutase, catalase and xanthine oxidase. A significant upregulation of all three biomarkers was observed in both treated individuals in laboratory experiments and field populations sampled from a pesticide use gradient. This study reports, for the first time, an increase in expression of xanthine oxidase in an invertebrate system (honey bees) exposed to pesticides.

Scale dependent drivers of wild bee diversity in tropical heterogeneous agricultural landscapes

Summary Factors associated with agricultural intensification, for example, loss of seminatural vegetation and pesticide use has been shown to adversely affect the bee community. These factors may impact the bee community differently at different landscape scales. The scale dependency is expected to be more pronounced in heterogeneous landscapes. However, the scale‐dependent response of the bee community to drivers of its decline is relatively understudied, especially in the tropics where the agricultural landscape is often heterogeneous. This study looked at effects of agricultural intensification on bee diversity at patch and landscape scales in a tropical agricultural landscape. Wild bees were sampled using 12 permanent pan trap stations. Patch and landscape characteristics were measured within a 100 m (patch scale) and a 500 m (landscape scale) radius of pan trap stations. Information on pesticide input was obtained from farmer surveys. Data on vegetation cover, productivity, and percentage of agricultural and fallow land (FL) were collected using satellite imagery. Intensive areas in a bee‐site network were less specialized in terms of resources to attract rare bee species while the less intensive areas, which supported more rare species, were more vulnerable to disturbance. A combination of patch quality and diversity as well as pesticide use regulates species diversity at the landscape scale (500 m), whereas pesticide quantity drove diversity at the patch scale (100 m). At the landscape scale, specialization of each site in terms of resources for bees increased with increasing patch diversity and FL while at the patch scale specialization declined with increased pesticide use. Bee functional groups responded differentially to landscape characteristics as well as pesticide use. Wood nesting bees were negatively affected by the number of pesticides used but other bee functional groups were not sensitive to pesticides. Synthesis and Applications: Different factors affect wild bee diversity at the scale of landscape and patch in heterogeneous tropical agricultural systems. The differential response of bee functional groups to agricultural intensification underpins the need for guild‐specific management strategies for wild bee conservation. Less intensively farmed areas support more rare species and are vulnerable to disturbance; consequently, these areas should be prioritized for conservation to maintain heterogeneity in the landscape. It is important to conserve and restore seminatural habitats to maintain complexity in the landscapes through participatory processes and to regulate synthetic chemical pesticides in farm operations to conserve the species and functional diversity of wild bees.

Bird species assemblages across a rural urban gradient around Kolkata, India

Urban development leads to changes in habitat structure and resource base. Bird communities are known to respond sharply to such changes. Our result from study of bird community along urbanization gradient around Kolkata metropolitan city clearly separated the urban bird community from the rural and rural 3 habitats in terms of species diversity and foraging groups. Rural and rural 3 sites had more number of rare species and higher percentage of unique species as compared to the urban habitats. Functional group analysis showed higher abundance of granivores in urban habitats and absence of insectivore and carnivorous species that were found in the rural and rural 3 habitats. The bird species assemblage along the gradient was significantly nested where bird species recorded in urban areas were subset of the species rich rural areas. There was no difference in individual counts between urban and rural habitats, therefore nullifying the hypothesis that rural areas are more species rich because of higher population size. Bird community in the urban areas was less even as compared to the rural areas due to the dominance of omnivorous guild. Bird diversity was negatively correlated to the density of house lots.

Field populations of native Indian honey bees from pesticide intensive agricultural landscape show signs of impaired olfaction

Little information is available regarding the adverse effects of pesticides on natural honey bee populations. This study highlights the detrimental effects of pesticides on honey bee olfaction through behavioural studies, scanning electron microscopic imaging of antennal sensillae and confocal microscopic studies of honey bee brains for calcium ions on Apis cerana, a native Indian honey bee species. There was a significant decrease in proboscis extension response and biologically active free calcium ions and adverse changes in antennal sensillae in pesticide exposed field honey bee populations compared to morphometrically similar honey bees sampled from low/no pesticide sites. Controlled laboratory experiments corroborated these findings. This study reports for the first time the changes in antennal sensillae, expression of Calpain 1(an important calcium binding protein) and resting state free calcium in brains of honey bees exposed to pesticide stress.

Differential Effect of Fruit Availability on Avian Frugivore Guilds in a Moist Deciduous Forest of India

Frugivores provide a critical ecosystem service by dispersing seeds and therefore play a major role in the survival and maintenance of trees in tropical forests. Avian frugivores constitute one of the major guilds in tropical forests whose activities are significantly governed by the availability of fruits across space and time. In our current study we examined the effects of the spatial and temporal pattern of food availability on avian frugivores and various avian frugivore functional groups in particular. We found a differential effect of fruit density and number of tree species in fruiting on different functional groups of avian frugivores along both spatial and temporal scales. Total frugivore density was best explained by ‘number of tree species in fruiting’ at both special and temporal scale. The variation in large frugivore density was best explained both by ‘fruit density’ and ‘fruit density’ and ‘number of tree species in fruiting’ together. This pattern was observed at a spatial scale but not along temporal scale. Along temporal scale large frugivore density was best explained only by ‘number of tree species in fruiting’. The medium sized frugivore density was not significantly explained by either ‘fruit density’ or ‘number of tree species in fruiting’. The medium sized frugivores are dependent both on insects and fruits and variation in insect density may determine spatial and temporal variation in medium sized frugivore density. The mixed diet frugivore group with a smaller gape width is limited by the variety of fruit they consume and thus their population was significantly controlled by the number of fleshy fruited tree species in fruiting along spatial scale. We observed breeding synchronization during the time of fruiting peak and we suggest that this could be a strategy for effective seed dispersal. Our study indicated very strong dependability of the large frugivore (dependent only on fruit) population on fruit availability unlike the mixed diet frugivore guild (fruit as secondary diet).

Habitat characteristics shaping ant species assemblages in a mixed deciduous forest in Eastern India

Environmental complexity and spatial heterogeneity are important factors influencing the structure of ant species assemblages. This paper documents the effect of different vegetation and environmental factors on ant community structure and functional group composition in different habitat patches. Ants were sampled at 16 sites distributed across five habitat types in the Kuldiha Wildlife Sanctuary. Sampling was performed 10 times over a 2-y period using pitfall traps. A total of 100 species belonging to 41 genera were collected during the study. Ant species richnesswasbestexplainedbyacombinationofpercentagegrasscover,percentagelittercoverandnumberofsaplings whereas percentage litter cover and soil nitrogen concentration significantly explained the variation in ant species abundance. Dominant Dolichoderinae were present only at forest edge and were found to be associated positively with percentage bare ground cover and negatively with percentage litter cover. Generalized Myrmicinae, subordinate Camponotiniandtropicalclimatespecialistswereprevalentinshadedforesthabitatswhereasopportunistsweremore common in two types of open habitat. Our study underpins the influence of vegetational complexity, litter and soil chemical properties on the structureand composition of ant species assemblages and various functional groups across forested habitats in this little-studied region.

Seasonal Changes in Zooplankton and Macro-fauna Populations of the East Calcutta Wetland Fish Ponds

Abstract The current study was to explore the seasonal variation in the zooplankton and aquatic macroinvertebrate population in India’s oldest and largest sewage fed fish ponds of East Kolkata Wetlands and whether they show different trends from the natural ponds. Zooplankton diversity was significantly higher in fish ponds whereas macroinvertebrate diversity was higher in natural ponds. Zooplanktons showed significant seasonal variation in the natural ponds but did not show any variation throughout the year in sewage fed fisheries. Among zooplankton species Brachionus spp., Keratella tropica which are pollution (eutrophy) indicator were found in greater abundance in EKW fisheries than natural ponds. Chironomid larvae which thrive and flourish in highly organically polluted or eutrophicated waters were dominant in EKW. The regular input of sewage provides a certain high level of nutrient to the fisheries which help to maintain greater and consistent population density and diversity of zooplanktons forming a strong base for the food webs in the EKW ponds.

Planktons in Dirty Water: Carbon Cycling Process of Sewage Fed Fisheries in East Kolkata Wetland, India

East Kolkata Wetland (EKW), a Ramsar site located in West Bengal, India is unique in the world as domestic city sewage is utilized here by the fishermen as fish feed. It is important to understand the nutrient cycling pathways of this unique ecosystem in relation to the biotic communities in order to assess its health and sustainability. This study examined plankton community structure in relation to the nutrient cycling pathways and various abiotic parameters of the sewage fed fisheries of EKW in comparison to the control ponds. RDA analysis show alkalinity and water temperature are the major environmental regulators controlling phytoplankton and zooplankton communities. Results of backward stepwise linear regression indicate dissolve carbon di-oxide and water pH play important role in gross primary production in sewage fed system. As plankton communities play an important role in transport and conversion of various carbon forms like soil organic carbon, particulate organic carbon, dissolve carbon di-oxide and soil inorganic carbon, the current study has presented a conceptual model of carbon flow in the EKW fish ponds and suggests replicability of such system elsewhere for city sewage management.

Pollinator Limitation and Crop Production: Experimental Observations on Few Economically Important Vegetable Crops in West Bengal, India

Pollination limitation and its impact on agricultural production is a serious concern of recent time. Assessment of the extent of dependency of various pollinator dependent crops on insect pollination assumes importance in this context. On the other hand, measures for restoring the pollination service needs to be explored for sustainable production of economically important crops particularly for the benefit of the small and marginal farmers. The present study aimed to assess the extent of insect pollinator dependency of brinjal (eggplant) fruit production and impact of honey bee (Apis cerana F) box introduction on the production in vegetable farms of North 24 Parganas, West Bengal, India. Through a pollinator exclusion experiment using enclosures it was found that brinjal fruit production reduces by 54.5xa0% when they are pollinator limited. This finding is in contrast with earlier report of 25xa0% dependency. The flower density in a pollinator limited environment was observed to increase by 31xa0%. This might be plant’s response to pollinator limitation where the plant invests more on reproductive structure than vegetative structures. However, this requires further exploration. Introduction of bee boxes in brinjal, pumpkin and pointed gourd farms showed significant increase in fruit production. This indicates both pollination limitation as well as the need for increasing the pollinators in the crop field for sustainable crop production.

Field Populations of Wild Apis cerana Honey Bees Exhibit Increased Genetic Diversity Under Pesticide Stress Along an Agricultural Intensification Gradient in Eastern India

Abstract Pesticides have been reported to be one of the major drivers in the global pollinator losses. The large-scale decline in honey bees, an important pollinator group, has resulted in comprehensive studies on honey bee colonies. Lack of information on native wild pollinators has paved the way for this study, which highlights the underlying evolutionary changes occurring in the wild honey bee populations exposed to pesticides along an agricultural intensification landscape. The study reports an increased genetic diversity in native Apis cerana Fabricius (Hymenoptera: Apidae) populations continually exposed to pesticide stress. An increased heterozygosity, evidenced by a higher electrophoretic banding pattern, was observed in the pesticide-exposed populations for two isozymes involved with xenobiotic metabolism—esterase and glucose-6-phosphate dehydrogenase. Differential banding patterns also revealed a higher percentage of polymorphic loci, number of polymorphic bands, Nei’s genetic distance, etc. observed in these populations in the Randomly Amplified Polymorphic DNA–Polymerase Chain Reaction (RAPD–PCR) experiments using three random decamer primers. Higher heterozygosity, being indicative of a more resistant population, implies population survival within the threshold pesticide stress. This study reports such changes for the first time in native wild Indian honey bee populations exposed to pesticides and has far-reaching implications on the population adaptability under pesticide stress.