Wild Bees Contribute to the Pollination of Apple Orchards in Western Kentucky

Importance of wild bees in agriculture

Almost 60% of wild flowering plants on Earth exhibit entomophily (i.e., need insects to be pollinated), and about 80% of our crops depend on insects to be successfully pollinated and even to increase their commercial value. Certainly, bees deserve the first place among pollinators so they have been declared the most important living organisms. Although not all crops need to be necessarily pollinated by bees, the truth is that wild bees such as bumblebees and many other solitary bees are usually the most effective pollinators for many economically important crops.

The astonishing diversity of wild bees

There are common questions about wild bees such as: Do they produce honey, do they have queens, and do they live in hives? The answers are no. Wild bees are mostly solitary, this means females are in charge of building the nest, bringing food (pollen and nectar), and laying eggs. In the United States, over 4,000 species of wild bees are known! In fact, the southwestern region of the country is one of the largest bee biodiversity hotspots across the world (Figure 1).

Figure 1. Diversity of wild bees in the Americas. Map from Orr et al. (2021). Darker colors indicate a higher number of species.

What about our apple orchards and their pollinators?

Apple orchards are a good example of bee-pollinated systems. In other words, we have apples every year because of bees. In fact, a recent study suggested that apple production is driven by wild bees. This may be a well-known fact among horticulturists and apple farmers. Many apple growers spend thousands of dollars a year to rent or keep honeybee colonies, so their apples trees are pollinated, increasing yields. In Kentucky, apple production is mainly for retail (direct marketing) and the local demand for quality fruits is increasing. In this scenario, we could think about both honey bees and wild bees as an essential element in apple production. In western Kentucky, specifically at the Research and Education Center in Princeton, apple trees were blooming during mid-April (Figure 2). As expected, different wild bees were actively visiting the apple flowers during the sunny and warm days (Figures 3 to 7).

Figure 2. Experimental apple orchard at the University of Kentucky, Research and Education Center, Princeton, KY. Picture credit A. Falcon.

Among the bee species we found in the UK- Research and Education Center at Princeton there were honey bees (Figure 3), mason bees (Figure 4), two sweet bee species (Figures 5 and 6), carpenter bees (Figure 7), bumble bees, leaf cutter bees, and mining bees. This is just a glimpse of some of the most common bees found visiting the apple flowers. In one survey, 80 bee species were identified visiting apple orchards in Ithaca, NY. Although we all know the benefits of honey bees to agriculture, we should not overlook the diversity and importance of wild bees in our orchards.

Figure 3. Honey bee (Apis mellifera). Honey bees are generalists, which means they do not prefer specific plant species (or families) to obtain pollen or nectar. You will find them in almost every habitat of North America. Picture credit A. Falcon.
Figure 4. Mason bee (Genus Osmia). Known to be among the most effective pollinators of apples and alfalfa, mason bees use hollow branches or stems to nest. They use mud walls to separate their brood cells. The red arrow shows the scopal hairs useful to collect massive amounts of pollen, a distinctive character of the family Megachilidae. Picture credit A. Falcon.

Figure 5. Sweat bee (Tribe Augochlorini). Small-sized bees easily recognized by their bright metallic color. They build their nests in the soil. Picture credit A. Falcon.

Figure 6. Sweat bee (Genus Dialictus). These small bees are often confused with flies, wasps or another tiny bug. However, they can be so abundant in some systems, thus they are good pollinators. Dialictus bee nest in the soil in small aggregations. Species are so similar, so an expert eye is required to identify them. Picture credit A. Falcon.

Figure 7. Carpenter bee (Xylocopa virginica). Since they are large and buzzy, carpenter bees are most likely confused with bumble bees, but they have solitary habits and build their nests in logs, trunks, or suitable wooden pieces (included man-made ones). They have such strong mandibles to chew wood out! Picture credit A. Falcon.

Additional information

We already know that too much of a good thing is never good, so a heavy use of honey bees can be adverse to the surrounding pollinator diversity.

Surrounding sources of pollen and nectar, namely annual blooming plants and forested landscapes, could increase the chances of having more wild bees visiting the apple flowers.

Pesticides are detrimental to bees and most beneficial insects. Their use must be applied according to the local legislation.

The U. S. Forest Service provides further information regarding the best gardening, landscaping, and conservation practices to keep our wild bees.

By Armando Falcon-Brindis, Research Analyst, and Raul T. Villanueva, Entomology Extension Specialist

Posted in Fruit
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