Review Of The Sublethal Impacts Of PesTicides On Native Indian Pollinators Case Studies In Honey Bees

By Priyadarshini Chakrabarti (Honey Bee Lab, Dept. of Horticulture, Oregon State University)

Importance Of Pollinators

Ecosystem services are the set of diverse ecological functions that are essential to human welfare. These services provide significant, measurable economic benefits. Pollination is the transfer of pollen from the male parts of a flower to the female parts of a flower of the same species, which results in fertilization of plant ovaries and the production of seeds. This phenomenon of pollination is ensured by pollinators leading to production of most of the fruit, vegetable and crop plants. Pollinators provide a crucial ecosystem service to both wild as well as cultivated plants. Crops like strawberry, apple, almond and melons show pollinator dependence of 0.25,0.65,0.65 and 0.95 respectively for production of seed set sand 87 crops, i.e. 70% of the 124 main crops used directly for human consumption in the world, are dependent on pollinators. Insect pollinators of crops and wild plants are under threat globally and their decline or loss can have profound economic and environmental consequences. Pollination essentially ensures global food security since agriculture largely depends on pollination.

Importance Of Honey Bees As Pollinators

Honey bees are extremely important pollinators and are perhaps the best studied among insect pollinators. They are also an essential component to agriculture and many crops are completely dependent to the pollination services provided by bees, often over a period as short as a few days . Bee pollination is essential for the production of a variety of agricultural crops, especially in horticulture. Honey bees play an important role in the maintenance of genetic diversity through the pollination of wild flowers which in turn provide food source for many small mammal and bird species, either through herbivory or by providing prey. The ecological and economic values of honey bees, in agroecosystems, hence is undeniable.

Importance Of Native Honey Bee Species

Extensive literature survey reveals that little is known about the sensitivities of other native Apis beesa part from A.mellifera with respect to any of the bio markers that have been used so far. There is a large information gap on the response of naturally occurring native honey bee populations (wild populations of non-exotic species) to multiple pesticide exposure in field conditions. In view of this, the focal species of this review are two native Indian honey bees spices :Apis dorsata and Apis cerana. Both the subspecies of honey bees are abundantly present in South Asia, especially in India. The Asian honey bee, Apis cerana occurs in southern Asia especially in the Indian sub continental desman aged for honey production and crop pollination, similar to western honey bees Apis mellifera. The distribution area of the giant honeybee Apis dorsata is similar to that of Apis cerana honeybee.

Pesticide As A Major Cause For Pollinator Decline

Exposure to pesticides

In recent decades, intensive agricultural practices have led to habitat destruction and increased pesticide use, resulting in a significant reduction in both the numbers and species diversity of wild bees and other beneficial insects. Pesticide use, apart from loss of natural vegetation cover, has been cited as one of the major drivers of the recent decline in pollinator populations. Foraging bees are exposed to let Hal insecticides when pollinating agricultural fields or foraging in residential settings. Additional mortality can occur when contaminated nectar and pollen are brought back to the hive.

Sublethal effects of pesticides on pollinator physiology and biochemistry

Antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) are of vital importance in an or genism’s defense against oxidative stress. Many pesticides, including organochlorines and carbamates, are known to causes significant oxidative stress. An elevated level of antioxidant enzyme activities is, therefore, a potential biomarker for oxidative stress for honey bees in pesticide laden environments and the same has been reported to occur in both the species of native Indian honey bees, thereby indicating a similar instance for other important native pollinators. Among other enzymes, xanthine oxidase (XOX) is a well known marker of oxidative stress and has been reported to increase under pesticide exposure. One fundamental requirement for a foraging bee’s survival is its ability to explore the surrounding and return back to hive. If pesticides, known to cause oxidative stress, begin to impede homing and foraging success in a forager, then the role of antioxidant enzymes in counteracting such (pesticide induced) stress would become critical.

Pesticide induced behavioral alterations in insect pollinators – olfaction

Resistance to insecticides is dependent on behavior (avoidance and repellence) and morphology (thickened cuticle providing a natural barrier). Of the numerous behavioral responses, this review focuses on one major neuroethological perspective – olfaction. Olfaction plays a crucial and determining role in mediating most of the responses including discovering food resources and ultimately survival of the foragers. A number of early studies have upheld the “odor search hypothesis” where the studies assumed olfactory cues extremely important for nectar and pollen search by honey bees as the honey bees were reported to use their antennae to locate food rewards. Caste-specific pheromonal communication in honeybees determines mating, alarm, defense, orientation, self-colony recognition and incorporation of all conducts within the hive. Hence, the importance of faction, in the recognition and sustenance of the various tasks within the hives undeniable. Honey bees, like other insects, are constantly exposed to numerous random odor stimuli which they use to syn the size consequential information. Proboscis extension response / reflex (PER) has been greatly used to check the effects of pesticides on honey bee olfaction. Odor detection starts with the help of olfactory receptor neurons (ORNs) located below cuticular structures on the antennae, called sensilla. Scanning Electron Microscopy (SEM) studies have helped identify the significantly reduced antennal sensilla types and number in pesticide-exposed populations of A. cerana. In order to comprehend there urinal processes fundamental tool factory learning, biophysical properties such as ion channel activity have been reported within the neurons of the olfactory pathway in the honey bee brain. Long term memory(LTM) formation and its role in effective olfaction is an important survival strategy of the honey bees. It has been reported that Ca2 + may be the preliminary trigger for LTM development. Calcium imaging studies have helped understand howl factory in formations correlated with pesticide exposures by studying biologically active free Ca2 + in the two major olfactory regions of the honey bee brain – mushroom body and antennal lobe regions.

Genetic diversity in natural populations of pollinators exposed to pesticides

Despite pesticides tress, some honey bee colonies do survive in the in tensive Agri cultural field sites – even though in dwindling numbers. It is possible that they are able to cope with the stressed environment by developing genetic heterozygosity. Metals, organic and inorganic pollutants, like pesticides, are reported to cause physiological poisoning by becoming attached to or by being absorbed by the cellular components that may lead to various effects, including alterations of genetic system, that are related to inhibition or alteration of enzyme alleles. While the level of genetic diversity in free living population scan boost their coping ability to stress, improved heterozygosity therefore has conservation significance. It tends to been enhanced in stressed outlier populations. At the physiological level, this enhancement is support- ed by the favoring of heterozygotes, especially when energy demands needed to adapt to stress are high. Assessing genetic diversity at both protein and DNA level scan prove to be beneficial for testing genetic diversity between populations. It was reported recently that populations of native cerana, exposed to pesticides over a long period of time, has shown increased genetic diversity at both protein and DNA levels. These studies help under-stand how pesticide as a stressor help shape population dynamics and threaten our important pollinator populations.

Conclusion

Sub lethal effects of pesticides have major impactson honey bees. With decline in the abundance and diversity of flowers, increased exposure to cocktail so agrochemical sand simultaneous us exposure to novel parasites accidentally spread by humans, bees are on a steady global decline. Climate change is likely to exacerbate these problems in the future. Stressors do not act in isolation; for example, pesticide exposure can impair both detoxification mechanisms and immune responses, rendering bees more susceptible to parasites. It seems certain that chronic exposure to multiple interacting stressors is driving honey bee colony losses and declines of wild pollinators. Studying all these interactions experimentally, poses a major challenge. In the meantime, taking steps to reduce stress on bees would seem prudent; incorporating flower- rich habitat into farmland, reducing pesticide use through adopting more sustainable farming methods, and enforcing effective quarantine measures on bee movements are allpractical measures that should be adopted.

Did You Know

• A honey bee visits 50 to 100 flowers during a collectio trip.
• A honey bee can fly for up to six miles, and as fast as 15 miles per hour.
• The bees’ buzz is the sound made by their wings which beat 11,400 times per minute.
• Honey is incredibly healthy and includes enzymes, vitamins, minerals. It’s the only food that contains “pinocembrin”, an antioxidant associated with improved brain functioning.

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