Two native andrenid bee pollinators face severe population declines in the semi-arid environments of Northwest India

Pollinator declines at the global level are the major concern of ecologists. Two ground nesting native andrenid bee species are important part of the pollination services of Northwest India. These include, Andrena savignyi Spinola an important wild pollinator of some major oilseed crops of the family Brassicaseae, and Andrena leaena Cameron an important wild pollinator of some spices crops of the family Umbelliferae, and vegetable crops of the families Brassicaceae, Apiaceae and Leguminoseae. Their importance in the agroecosystems of Northwest India notwithstanding, the actual status of their populations in such habitats is not known. The purpose of this study is to explore the latter aspect of these bees in Northwest India. A survey was conducted on the abundances of two andrenid species foraging on their respective host plants from 1990 to 2015 at an interval of 5 years. I counted the number of foraging bees of the two species on two crops viz. Andrena savignyi on a winter-flowering crop, raya (Brassica juncea) and Andrena leaena on a summer-flowering crop, carrot (Daucus carota). In 25 years, the foraging populations of Andrena savignyi declined from 4.16±0.168 bees/m2 in 1990 to 1.2±0.09 bees/m2 in 2015 and of Andrena leaena from 5.24±0.156 bees/m2 in 1990 to 1.4±0.11 bees/m2 in 2015. This decline in the numbers of foraging bees seemed to be caused by the habitat loss and poisoning of these bees due to the excessive and indiscriminate use of weedicides in the wheat and rice crops grown in this region. Viewing the importance of these bees in the pollination of crops, it is suggested that, habitat of these bees be conserved and, if at all necessary, weedicides safe to the soil nesting bees be use

Abundance, foraging behavior and pollination efficiency of insects visiting the flowers of Aonla (Emblica officinalis)

Many insect species visit the flowers of a plant and play an important role in their pollination. Of late, the interest of the pollination biologists has been to determine their relative contribution towards the reproductive success of the plant. Such information is lacking on the pollinators of Aonla (Emblica officinalis Gaertn.), a plant of very high nutritive and medicinal importance. Therefore, let’s attempt to make this study to generate such information on this plant. The study was conducted on three varieties of Aonla (viz. Chakaiya, NA-7 and NA-10) for two years. An entire range of flower visitors of this fruit plant was captured with hand net from its field during its flowering period and were identified. On the basis of foraging mode, the flower visitors were characterized as pollinators and non-pollinators. Their abundances, foraging rates, activity durations and number of pollen grains carried on the surface were recorded, and these parameters were used to determine their relative contribution towards the reproductive success of this plant. Among the 12 insect species visiting the flowers of Aonla at the study site, 5 belonged to Hymenoptera, 6 to Diptera and one to Lepidoptera. Apis dorsata was the most abundant visitor having maximal foraging rate and carried maximal number of loose pollen grains, followed by A. mellifera, A. florea and Sarcophaga sp; other visitors had lesser values of these parameters. On the basis of these parameters, melittophilous mode of pollination was found to predominate in Aonla. However, the plant was found to be benefitted from the multispecies pollinator guild, and the pollinator diversity seemed to matter for maximization of pollination in Aonla. Therefore, there is a dire need to conserve the pollinator diversit

Abundance, foraging behavior and pollination efficiency of insects visiting the flowers of Aonla (Emblica officinalis)

Many insect species visit the flowers of a plant and play an important role in their pollination. Of late, the interest of the pollination biologists has been to determine their relative contribution towards the reproductive success of the plant. Such information is lacking on the pollinators of Aonla (Emblica officinalis Gaertn.), a plant of very high nutritive and medicinal importance. Therefore, let’s attempt to make this study to generate such information on this plant. The study was conducted on three varieties of Aonla (viz. Chakaiya, NA-7 and NA-10) for two years. An entire range of flower visitors of this fruit plant was captured with hand net from its field during its flowering period and were identified. On the basis of foraging mode, the flower visitors were characterized as pollinators and non-pollinators. Their abundances, foraging rates, activity durations and number of pollen grains carried on the surface were recorded, and these parameters were used to determine their relative contribution towards the reproductive success of this plant. Among the 12 insect species visiting the flowers of Aonla at the study site, 5 belonged to Hymenoptera, 6 to Diptera and one to Lepidoptera. Apis dorsata was the most abundant visitor having maximal foraging rate and carried maximal number of loose pollen grains, followed by A. mellifera, A. florea and Sarcophaga sp; other visitors had lesser values of these parameters. On the basis of these parameters, melittophilous mode of pollination was found to predominate in Aonla. However, the plant was found to be benefitted from the multispecies pollinator guild, and the pollinator diversity seemed to matter for maximization of pollination in Aonla. Therefore, there is a dire need to conserve the pollinator diversit

Some Unresolved Issues of Measuring the Efficiency of Pollinators: Experimentally Testing and Assessing the Predictive Power of Different Methods

Knowledge of efficiency of pollinators is valuable in the derivation of (i) the degree of mutualism specialization of a flower visitor in the natural plant communities, (ii) the optimum number of pollinators needed for the maximum pollination in a plant population, and (iii) the pollinator risk assessment in the sustainable agriculture. Earlier researchers used many direct and indirect methods for measuring the pollination efficiency (PE) of flower visitors. However, a great ambiguity exists in the usage of this terminology that necessitated its fresh scrutiny. I tested the available three standard methods afresh to find the efficiency of pollinators. These included comparing the (i) number of pollen grains removed and deposited by the visitors; (ii) seed set resulting from a single and the multiple visits of the visitors; and (iii) “pollen transfer efficiency (PTE)” derived from the foraging behavior and abundances of the visitors. Observations were recorded on the visitors of four plant species in an agroecosystem of Northwest India. These plants represented a wide variety of the floral types across the angiosperms. The first two methods, namely, the “number of pollen grains removed and deposited” and the “seed set resulting from a single and the multiple visits,” were appropriate in finding differences between the efficiency ranks of the pollinators of those flowers where the number of deposited pollen grains was less than the number of ovules in the ovary. However, these two methods completely failed in situations where exactly reverse condition of pollen grains and ovules existed. Thus, these two methods of measuring the PE of visitors had limited approach and lacked a universal application over the entire angiosperm taxa. On the other hand, use of “pollen transfer efficiency”, derived from the foraging behavior and abundance of the visitors, seemed to have an edge over the other two methods as this was helpful in finding differences between the efficiency ranks of the pollinators of plants in all the three situations tested in this study. However, validation of all the three methods through the plant reproductive potential seemed to be an integral confirmatory step for drawing inferences about the efficiency of pollinators

Pollination Ecology of Rocket (<i>Eruca vesicaria</i> (L.) Cav. ssp. <i>sativa</i> (Mill.) Thell) in the Semi-Arid Environments of Northwest India: Native Bees Are the Major Pollinators

Several insect species visit the flowers of a plant to obtain floral rewards in the form of pollen and/or nectar. In return, we would anticipate that those visitors would contribute to the reproductive success of the plant. Do these visitors contribute equally towards the reproductive success of the plant? This issue has been the interest of many pollination ecologists. To find a solution to this problem, I investigated the pollination ecology of rocket (Eruca vesicaria (L.) Cav. ssp. sativa (Mill.) Thell), an important leafy vegetable used as salad. I captured the flower visitors with a hand net from the experimental field and had these identified. I also recorded the number of loose pollen grains carried on the body of the visitors of different species and deposited on the stigmas. Effects of single and multiple visits of visitors on the seed set of rocket flowers were also determined. Abundances and foraging rates of the flower visitors of this species were recorded and their values were used to calculate their respective contributions towards the reproductive success of this species. Five species of Hymenoptera, three of Diptera, one of Lepidoptera, and one of Coleoptera visited the flowers of the rocket. Apis florea was the most abundant among the flower visitors, followed by the dipterous flies, Apis mellifera, Apis dorsata, Andrena savignyi, and Andrena leaena in descending order. The number of loose pollen grains carried and deposited, foraging behaviors, foraging rates, and abundances did not provide conclusive measures to differentiate the contributions of different flower visitors towards the reproductive success of the rocket. However, the data recorded on abundances, foraging behaviors, and foraging rates together could do so. Accordingly, Andrena savignyi was the most efficient pollinator of rocket, followed by Andrena leaena, Apis dorsata, Apis mellifera, and Apis florea; dipterous flies were the least efficient pollinators of this plant species. In rocket, 28.84% of pollination was brought by Andrena savignyi, 24.69% by Andrena leaena, 20.34% by Apis dorsata, 18.37% by Apis mellifera, and 7.7% by Apis florea; dipterous flies caused only 0.06% pollination. Butterflies were very rare and Coccinella sp. was not a pollinator of this plant. Therefore, not all the pollinators of rocket contributed equally towards its reproductive success (seed production). Bees brought about 99.94% of total pollination and melittophily distinctly predominated over other pollination modes. However, among the bees, native bees together are the major pollinators in the flowers of rockets and accomplished more than 81.5% pollination. Therefore, the conservation of native bees is most important for the pollination of crops such as rockets