Pollination and seed setting in Lucerne
K Vet Og Landbohojskole Arsskr : 138-169
On the basis of counts made in isolation, self-tripping was found to be small under Danish conditions. Usually there are more self-tripped flowers in Du Puits lucerne, than in Otofte, Otofte-Grimm and Canadian-Grimm. Self-tripping generally causes self-pollination, but a possibility of cross-pollination cannot be completely disregarded. The numbers of wild bees per hectare vary greatly. On an average there will be no more than 75 Melitta females and 50 bumble bees per hectare. These trip about 95 per cent and 80 per cent respectively of the flowers visited, and visit about 14 and 12 flowers per minute. Apis mellifica on an average trips about 2.8 per cent. and Apis mellifica var. ligustica and crosses between the two varieties about 2.1 per cent of the flowers visited. The honey bees average about 13 visits per minute. Assuming the presence of about 8000 honey bees per hectare, these bees will carry out 57 per cent of the trippings, Melitta 28 per cent. and bumble bees 15 per cent. About 97 per cent. of the visits by honey bees are "oblique", about 2 per cent "straight", about 1/4 per cent of the visits take place "on the standard" and about 1/2 per cent of the visits are carried out in flowers which have been tripped. About .5 per cent of the "oblique" visits, 75 per cent of the "straight" and about 75 per cent of the visits "on the standard" result in tripping. The total number of trippings caused by the more haphazard movements of the honey bee in flowers was only . 1 per cent of the total numbers of visits Apis mellifica appears to have a greater tendency to go "straight" in than Apis mellifica var. ligustica and crosses between the two varieties. Seed setting after self-tripping or without tripping is decidedly of minor importance in Denmark. About 1 to 2 seeds were produced per cross-pollination, depending on the strain used. Du Puits generally showed a greater cross-fertility than Otofte, Otofte-Grimm and Canadian-Grimm. The number of apparently normal well-developed seeds produced after cross-pollination was only 60 to 70 per cent. of the total number. In spite of unfavorable weather conditions about 1 seed per tripping was produced after visits by honey bees. This agrees fairly well with the results after cross-pollination for the corresponding periods. It is probable that trippings by honey bees mainly result in cross-pollination. Fertility is greatly influenced by the more or less favorable exposure of the flowers to light and wind.