Impacts of climatic variables on pollinator abundance, flower blooming and yield of Apple in Kumaun, West Himalaya, Uttarakhand, India

Apple (Malus domestica, Family Rosaceae), an important cash crop, relies on insect pollination. Climatic variables (temperature, humidity and light intensity, etc.), impact on flowering and insect visitation activity of apple thereby influencing pollination. The activity of bees and other visitors varies throughout the flowering period. However, precise information on such impacts is meagerly available.

Towards understanding impacts of climatic variable on insect pollination and apple production, eight apple orchards in Ramgarh region of Kumaun in Indian west Himalaya were intensively investigated. The work plan included recording of phenological observations, pollinator density and diversity, and yield data as per the protocols developed under Global Pollination Project by FAO (2011). For the climatic variables (temperature, Humidity and light intensity) of same day was considered and for the production the number of fruit set, total yield per tree was recorded. Diverse insect visitations were recorded during the blooming period of apple that included honey bees, wild bees, wasps, hoverflies and other insects (i.e., butterflies, lady bird, flies and beetles).

It was revealing that the climatic variable affected the flowering phenology and the visitation rate of the insects/pollinator diversity and also impacted on the number of fruit setting and production. The increasing temperature (Maximum and Minimum) the number of open flowers (p < 0.05) increased along with the increased visits of other insects (r = 0.199; p < 0.05). Light intensity, however, showed positive response of the honey bees (r = 0.246; p < 0.01) and hoverflies (r = 0.302; p < 0.01). On the contrary, humidity exhibited negative relationship with the honey bees (r = -0.272; p < 0.01), hoverflies (r = -0.335; p < 0.01) and other insects (r = -0.189; p < 0.05). With the increasing number of open flowers the number of insects visitors diversity of honey bees (r = 0.424; p < 0.01), hoverflies (r = 0.295; p < 0.01) and other visitors (r = 0.261; p < 0.01) increased significantly. While considering yield data, number of fruits per tree showed significant positive relationship with the visit of honey bees (r = 0.325; p < 0.01) and hoverflies (r = 0.421; p < 0.01).

Therefore, the study concluded that the apple yield is sensitive to pollinator (insect visitor) density. This calls for adopting best practices for pollinator conservation and management so as to harness optimal yield of apple in the region.