I

ANNO 3 Numero 2
Mauro Pinzauti [1], Pasquale Mariniello [2]

Solitary bees for seed production in entomophilous forage crops

[1] Dipartimento CDSL - Entomologia agraria, Università di Pisa, Pisa, Italy
[2] CRA - Istituto sperimentale per le colture foraggere, Foggia, Italy

Corresponding author: ecarpana@inapicoltura.org

The industrial seed production in two allogamous forage crop species: lucerne (Medicago sativa L.) and berseem (Trifolium alexandrinum L.), depends on agronomic techniques, weather conditions and pollinating insects’ activity.

Pollination studies were carried out during the years 1977-1999 in the province of Foggia, an area in the South of Italy site with a typical Mediterranean environment. The forage crop variety used in the experiment was “Equipe”, for lucerne, and “Sacromonte “, for berseem. These varieties are the most popular in southern Italy for hay and seed production.

The solitary bees used in the “pollination service” were the mason bee (Osmia rufa L. – for berseem) and the leafcutter bee (Megachile rotundata F. – for lucerne). Megachilidae adult insects were released in the centre of the test field during the flowering period (about 30 days). The time of release was at the end of April and June, respectively for the mason bee and the leafcutter bee. The behaviour of the two bee species was found to be influenced by the prevailing weather conditions during the forage flowering time and the pollination efficacy resulted to be dependant on the distance from the insect nest-trapping point. Seed production was influenced by bee activity and the number of seeds per fructiferous organ was the most evident effect of the pollinating activity in both varieties of forage crops.

The efficiency of the bee-pollinator activity on seed yield in lucerne was evident up to the 9th transect (80 m from the nest), after which the pollinator effect gradually degraded up to the 12th sector; in berseem instead, the increase in seed yield remained constant until the 10th transect and then declined in the last two transects. On average the seed yield increase promoted by pollinator activity was 46% in lucerne and 25% in berseem.