Pollinators and crops in Bhutan: insect abundance improves fruit quality in Himalayan apple orchards

Abstract

Apples are one of the most important global crops that relies heavily on insect pollination, which has been shown to increase apple production and value. However, recent reports indicate that apple production has been declining in certain regions, including in Bhutan. One of the potential causes of declining production are pollination deficits driven by a low abundance and diversity of pollinators, a phenomenon that has received little attention in Bhutan to date. Here, we present the first study examining the diversity of flying insects in Bhutanese apple orchards in relation to apple quality. During the apple flowering season, 1,006 insects comprising 44 unique (morpho-)species from the orders Hymenoptera, Diptera, and Lepidoptera were recorded using a standardized method of passive and active trapping within nine different orchards in Thimphu, Paro, and Haa districts, in the western part of Bhutan. During the harvest season, 495 apples were collected from these nine orchards, and we measured five different parameters; weight, size, sugar concentration, seed number, and malformation score. The most dominant flower visitors across all orchards were honey bees (mostly Apis mellifera, followed by A. cerana and A. dorsata). Orchards with a higher abundance of flying insects (both managed and wild) had better apple quality (weight, size and sugar concentration). Contrary to reports from other regions of the world, flower visitor diversity did not correlate with the quality of the apples. This represents the first study reporting on apple pollination in Bhutan and highlights the importance of pollinators and reinforces the need to develop pollinator friendly practices to ensure sustainable apple production.

Global taxonomic, functional, and phylogenetic diversity of bees in apple orchards

“…and their comparatively lower numbers (whether managed or not) compared to managed (eu)social bee species suggest that they might have a lower impact on local wild bee populations (Bosch and Kemp, 2001;Russo, 2016;Sedivy and Dorn, 2014). Our results are indicative of a global trend, namely the strong reliance by growers on A. mellifera for pollinating large monocultures of pollination-dependent crops (see Osterman et al (2021)) and should inform conservation initiatives to take into account the conservation of wild bee species and functional diversity (see also Dorji et al, 2022;Prendergast et al, 2021). Moreover, while sites with high levels of pollination might rely on a limited set of few pollinator species, sites with the lowest levels of pollination might rely on all bee species, including the rarest ones, to maintain sufficient pollination services (Winfree et al, 2018).…”

“…and Table A.1) following a strict and standardised protocol combining netting and pan trapping (Droege et al, 2010). Parts of this dataset have already been used in local or subcontinental studies to investigate the diversity of bees in apple orchards (Allen-Perkins et al, 2022;Dorji et al, 2022;Leclercq et al, 2022;Prendergast et al, 2021;Weekers et al, 2022b;Weekers et al, 2022a). Each site was sampled for three days (consecutive if weather permitting) during the peak blooming period.…”