Decline in number of pollinators reduces yield potential of crops

Indiscriminate use of pesticides has resulted in the decline of honeybee population in Idukki and Kasaragod districts, studies show.

S. Devanesan, Professor and Principal Scientist, All India Co-ordinated Research Project (AICRP) on Honeybees and Pollinators, College of Agriculture of Kerala Agricultural University, Vellayani, said indiscriminate use of pesticides caused disappearance of pollinators, especially honeybees. This, in turn, caused decline in yield potential of cardamom in Idukki district.

He said the scientists of AICRP who had visited Idukki to study the diversity of honeybees had found that Endosulfan had been used there under a different trade name. The day after the application of the pesticide, bees had showed symptoms of poisoning and died.

“The bees visited the flowers and returned near to the beehive but were unable to direct their flight to the hive entrance. The poisoned bees showed decreased aggressiveness and the paralysed bees crawled on nearby objects, resulting in reduced food storage and brood rearing and decline in population in the colony,” Dr. Devanesan said.

A decline in the number of feral colonies of honeybees as well as hived colonies had been observed in the areas. The observations in the plantations had revealed a drastic reduction in the fruit set of cardamom capsules in the areas where the pesticide use was high, he said.

Important role

Honeybees play an important role in pollinating flowering plants. They are the major pollinators in cardamom, coffee, coconut, cashew, many vegetables like cucurbits and leguminous plants including peas and beans. Honeybees have many qualities which help them to be a good pollinator, and all bee species are pollinators.

Koragas affected

A study by Thanal, a public interest research, advocacy, education and action trust here, showed that honeybees had been affected and almost wiped out in the Endosufan-sprayed areas of Kasaragod district. It affected the tribal community of Koragas, most of whom used to collect honey from the forests, and traditional organised beekeepers. Many keepers had witnessed mass kill of bees following spraying of Endosulfan by the State-owned Plantation Corporation of Kerala.

A survey and analysis conducted by M. Lakshmi Narasimhan and C. Jayakumar of Thanal among 31 beekeepers showed that the annual production of honey by beekeepers had been 12,015 kg before aerial spraying of Endosulfan started.

That had come down to 68.5 kg in mid-'80s when the spraying had been going on. After the ban on aerial spraying, the production rose marginally to 133 kg. Though half of the beekeepers had resumed operations after the spraying was discontinued, production failed to pick up proportionally.

Decline in production

In the case of 14 members of honey collecting Koraga tribe surveyed, the availability of forest honey had come down from 3,375 kg annually before Endosulfan spraying to 938 kg during Endosulfan spray. The financial loss calculated just for 45 beekeepers and collectors at the same production level as in 1970s but at prices of 2008 is estimated to be Rs.29 lakh annually. If that is projected for the whole of affected areas in the district, the financial loss could run into several crores of rupees, they observed.

The study indicated that the disappearance of bees had affected yield from areca nut trees in the area. Farmers complained that yield had gone down by half after the spraying had stared.


  • Bees die the day after pesticide application
  • Decline in number of feral and hived colonies

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