I have further researched pollination of both apricots and strawberries in France since my last letter. It turns out the GRAPP in conjunction with ADAPI has published a series of one-page leaflets on both plants, as well as recommendations for melons, kiwis and cherries.
J. Vilain of the GRAPP Méditerranée and P. Jourdan of ADAPI say that apricot growing in France has derived considerable energy from new varieties developed in north America. Most older European varieties were auto fertile; the new ones, however, are not and require both compatible pollinizer trees and insect pollinating vectors. Hybrid vigor of cross pollination enables earlier fruit development, better quality fruits and improved protection from freezing.
To ensure cross pollination, compatible pollinizer varieties can be interplanted in the orchard and/or boquets of the pollinizer can be hung in plastic bags of water in the orchard. This technology and also the use of pollen inserts requires a maximum of pollinating insect vectors (honey bees). Apricots are one of the earliest bloomers in the Provence-Alps-Côte d’Azur region. For maximum honey bee pollination, the leaflet suggests:
1. Colonies should have many young bees and be well-fed. Stimulative feeding 3 to 4 weeks before the bloom is recommended.
2. Three to 4 hives per hectare (2.47 acres) is recommended. For very early bloomers, depending on colony strength, six to eight colonies per hectare may be used.
3. Hives should be protected from the wind and exposed to the sun; a northern exposure in February is to be avoided at all costs. Hives should be placed throughout the orchard in groups of threes or fours for maximum pollination. They should be brought into the orchard just as flowering is beginning.
4. Insecticide treatments of trees can cause significant problems in both pollinating insect and pollen viability and must be avoided. Fungicide application can also affect pollen viability. Thus, all chemical treatments must be avoided during apricot bloom.
Chemical treatment in strawberries must also be avoided according to a leaflet entitled: Good Fertilization in Strawberries, 1996 by J. Vilain, GRAPP Méditerranée, Regional Chamber of Agriculture, Aix-en-Provence.. This leaflet is based on data collected in the 1995 growing year. There are a huge number of variables in getting good fertilization in this crop including:
1. Cold–a certain number of cold (below 8 degrees C) is required in strawberries depending on variety (600 hours for Favette; 1,000 hours for Belrubi). Unsuitable dormancy periods can result in small flowers and insufficient pollen. Too much cold, on the other hand, will result in more stem or stolon development and fewer flowers.
2. Heat–a major risk in plants grown under cover (greenhouses; plastic tunnels). At 35 degrees C germination of pollen for the variety “Valeta” is only 3 percent.
3. Illumination–as much as light as possible in the tunnel is important for the bees to orient. Too much humidity must also be avoided.
4. Colony placement–correctly locating colonies in plastic tunnels for strawberry pollination is important to ensure maximum efforts and minimal loss of bees. Colonies must be placed so that bees have access both to inside and outside the tunnel. The openings in the plastic allow the bees to escape at strategic places located along the length of the canopy and return to the hive via the permanent opening near the colony. These openings minimize bees being trapped under the plastic and dying. Hives shown in the leaflet are placed in the northwest part of the tunnel (see Trevor Weatherhead’s observations below).
In response to one of my earlier letters, I received the reply published below from Mr. Trevor Weatherhead of Australia who adds his knowledge to this area:
From: Trevor Weatherhead <firstname.lastname@example.org>(February 11, 1997)
I will list some experiences in Australia with hives in cages for pollination of the seed companies breeding programme. The cages would be similar to glasshouses and our experiences may be of some help.
Firstly, hives are placed outside the cage. In the middle of the day, a hive is placed inside the cage. This way the old field bees are left outside the cage and enter one of the adjoining hives. These old field bees are useless in a cage as they fly to the corners and do not pollinate.
Once inside the cage, the hive is placed in the top corner in the north west. In the northern hemisphere I would assume you would put it in the south west corner (Editor’s note: This is an interesting observation; information in my possession shows hives in the northwest sector of the greenhouse/tunnel). In our case, the north west corner is where the bees usually migrate to. As you only have younger bees in the cage, they will establish themselves within the cage and forage, thus pollinating.
It was found that the bees were not keen on a single floral source of pollen within the cage. In one case canola was being pollinated. They tended not to breed too well on the single pollen source. Pollen from other sources was added and egg laying picked up and hence there was brood to feed and a requirement for pollen. Foraging was increased.
You could use a pollen substitute or supplement instead of pollen and it would work just as well. I remember using one of the substitutes in a trial within a large enclosure where strawberries were being grown. It stimulated egg laying in a case where the queen had stopped laying and foraging activity had greatly diminished.
Sugar syrup feeding is also a help as most crops being pollinated in cages, or in your case glasshouses, tend to be shy on nectar. This can be feed in an external source within the cage or by a boardman feeder.
If the hive within the cage runs down, it can be swapped with one outside the cage and the process starts again. If more than one hive is required, it means you need to have a few more outside.