1. How Bees Carry Pollen to Strawberry Flowers in Winter
Strawberry flowers are insect-pollinated. When bees visit the flowers to collect nectar, pollen sticks to the fine hairs on their bodies and transfers to the flower’s center [2]. If pollination is incomplete, the strawberry grows into a misshapen fruit because the pollinated parts swell and turn red [2]. Because wild insects cannot be relied on for pollination inside greenhouses, farmers began introducing honeybees for pollination around 1968 [1]. Today, data shows that bees are used on 2,815 hectares out of 3,171 hectares of greenhouse strawberry fields, which is roughly 90% of the area [1]. Of the 6,031 hectares in total where pollination bees are used, strawberries account for about 47%, the largest share [1]. Because the area is counted cumulatively, treat "about 90%" as a rough guide only. An old test also shows what happens without insects: in a 1974 Iwate report, the share of misshapen fruit was 3.9 to 5.2% in forced-culture greenhouses where hoverflies (flies, not bees) were released, against 13.0% where they were not [6]. It is not a figure for honeybees, but it shows how hard pollination is without insects. But simply releasing bees is not enough; many factors must be managed carefully.
2. Why Farmers Wait 10 Minutes Before Opening a Beehive
When hives arrive at the greenhouse, the bees are excited from the vibration of transport. Manuals recommend leaving the hive closed for about 10 minutes to let them calm down before opening the entrance [2]. If the greenhouse temperature drops to 20°C or lower in the evening, the entrance should be opened after sunset [2]. Bees then fly around the hive to memorize its location, a behavior called orientation flight [2]. Once placed, the hive must never be moved. Even a small shift can leave some bees unable to find their way back [4][2]. The entrance should face the sun, and the hive should be placed in a visible spot at the same height as the flowers or slightly higher [2]. In high-bench cultivation, where plants are raised to waist height, bees often get lost, so placing a blue sign nearby helps them find their way [2]. As a general example, for long north-south greenhouses, hives are placed on the north side with entrances facing south; for east-west greenhouses, they go on the west side facing east [2]. Bees use ultraviolet light, which people cannot see, as a clue to find their position (people see about 400 to 800 nm, bees about 300 to 650 nm, and bees do not see red as a color). For that reason, special UV-blocking greenhouse film can make it hard for them to fly well, though not every film has this effect [3]. Hives must also be kept away from ventilation fans, as bees can be sucked in and unable to return [4]. Additionally, some UV-blocking films can confuse bees, as they navigate using ultraviolet light, which humans cannot see [3].
3. How Many Bees Does a Greenhouse Need?
A common guideline is to use one hive (about 6,000 to 8,000 bees) per 10 ares (1,000 square meters) [3]. This equals about 6 to 8 bees per square meter, or 10 to 13 bees per tatami mat (about 1.65 square meters) [3]. However, this is just a rough estimate that changes by region and season [3]. Farmers might think adding more bees is safer, but manuals state that increasing the number does not improve pollination rates [3]. Too many bees can run out of food, causing the colony to shrink instead of grow [3]. In very large connected greenhouses, farmers may place 2 or 3 hives [3].
4. How Farmers Protect a Beehive from Heat and Cold
Bees keep the center of their hive at about 33 to 34°C [2]. In greenhouses where daytime and nighttime temperatures vary greatly, bees must work hard to warm the hive at night and cool it during the day, which is a heavy burden [2]. Bees visit flowers most actively when the temperature is 20 to 25°C [2]. If it gets hotter, more bees fly, but fewer visit flowers [2]. Direct sunlight through the plastic can overheat the hive, so a shade roof is placed on top [2]. If the greenhouse reaches 30°C or higher, the inside of the hive can become dangerously hot [2]. In hot regions, some farmers place hives outside the greenhouse to avoid overheating, but they must add insulation if it gets cold [2].
5. How Farmers Keep Bees Pollinating for Six Months
Working bees in a greenhouse live only 1 to 2 months, but strawberries need pollination for nearly 6 months from autumn to spring [1]. To bridge this gap, new generations of bees must be born inside the hive [3]. Larvae need pollen to grow, so if flowers stop blooming, egg-laying stops, and bees may become insufficient at critical times [3]. Farmers may consult with beekeepers to provide substitute pollen [3]. Timing is also crucial; hives are introduced when flowers begin to bloom, not before, to prevent bees from wasting energy searching for food [2]. Bees also slow down their activity in cold or flower-scarce periods to live longer [2]. Regarding food, rented hives usually have enough honey stored, so no extra feeding is needed unless the beekeeper says otherwise [2]. Purchased hives may have less honey, so sugar water is given as instructed [2]. As feed, honey is not given [2]. Since methods vary by supplier, following the beekeeper’s instructions is essential [4].
6. Where Beehives Are Moved on Pesticide Spraying Days
Bees are very sensitive to pesticides. Even low-toxicity pesticides and fungicides can affect their behavior [5]. Therefore, the day before spraying, after the bees have returned to the hive in the evening, the hives are moved outside the greenhouse [5]. They are placed in a cool, shaded spot. In Kagawa Prefecture, the recommended storage temperature is 5 to 10°C [5]. When returning the hives, farmers must check the safety waiting period for each pesticide and place the hive back in its exact original location [4]. This is critical because moving a hive even slightly can cause bees to get lost, as noted earlier.
7. Why There Are Not Enough Pollination Bees
The Ministry of Agriculture states that there is no surplus of pollination bees [1]. Most beekeeping focuses on honey production, and recent natural disasters and diseases from mite infestations have made supply tight [1]. Farmers must manage hives well to keep colonies alive longer and improve survival rates when returning rented hives to beekeepers [1]. Other insects are also being studied. The Japanese black bumblebee and a type of fly called the "bee fly" (hirozukinbae, a kind of blowfly) are alternatives [1]. In some regions, deformed fruits appear frequently in February and March due to low temperatures and lack of UV light, which limits bee activity [7]. Research in Nara and Shimane Prefectures has explored using bee flies to help during these months, but this is still in the research planning stage, and effectiveness is not yet proven [7]. Also, honeybees can sting workers, which is a challenge for tourist farms [7].
8. How to Spot the Hives When Visiting a Strawberry Farm
If you visit a strawberry farm or direct sales shop, look into the greenhouse from a distance. Try to spot where the hives are placed. You can check the direction of the entrance, the height, nearby signs, and if there is a shade cover [2]. Safety: For safety, do not approach, touch, or shake the hives. Follow the farm staff’s instructions. If you feel uneasy, watch only from a distance. The information in this article comes from the Ministry of Agriculture, the Bee Association manuals, and Kagawa Prefecture pamphlets [1][2][4]. One question remains: what happens to the rented hives after they are returned to the beekeepers?