Declining abundance of pollinating insects drives falls in loquat (Eriobotrya japonica) fruit yields in the Pothwar region of Pakistan

Abstract

Insects perform numerous vital ecosystem services, so widespread reports of insect declines are of considerable concern. However, there are huge knowledge gaps with regard to the extent and scale of insect declines, with most studies being from Europe and North America and very few long-term data sets on insect population change in Asia, Africa or South America. The current study describes trends in abundance of insect pollinators visiting loquat (Eriobotrya japonica) over 13 years (2006–2018) in ten widely-spaced orchards in the Pothwar region of Pakistan. Results reveal a significant and concerning decline of 89.9% in overall abundance of flower-visitors across the study period. All pollinator species declined; for example numbers of Apis dorsata fell by 97%, A. mellifera by 96%, A. cerana by 93%, and Bombus haemorrhoidalis by 84%. Declines were non-linear, being most rapid in 2006–2009. In parallel, the average yield per loquat tree fell by 61%; sugar and organic acid content also declined. Total flower-visiting insect abundance was a strong predictor of crop yield and quality over time and across sites, while pollinator species richness was less powerful. Trees that were given supplemental pollination by caging them with small honeybee colonies during flowering showed no decrease in yield or fruit quality. These results indicate that declines in populations of wild pollinators are negatively impacting loquat production and the livelihood of the small farmers of the area. Further research to identify the cause of these insect declines is urgently needed, alongside development of conservation strategies for pollinators in this region.