S.I. Bees Liberated In North

Press, Volume CV, Issue 31027, 5 April 1966, Page 9

S.I. Bees Liberated In North

Two species of longtongued bumble-bees, hitherto limited to parts of the South Island, have been released in Palmerston North this summer and have established nests. If they become permanently established, they will play a useful part in ensuring good pollination of red clover in the North Island.

. This information was given by Professor W. C. Clark, head of the zoology department of Massey University, in a report to the university council.

The two species are Bom bus hortorum, which occurs in many South Island districts but never north of Amberley, and Bombus subterraneus, Which is common in the MacKenzie country but rare elsewhere.

The attempt to introduce the species was prompted by the increasing difficulty experienced by the Grasslands Division of the D.S.I.R. in obtaining sufficient pollinators for use in plant breeding work

with red elovers. This problem has become more important with the development of a tetrapioid red clover, whose flowers have a particularly long corolla tube. Mr L. Gurr, senior lecturer in zoology at Massey, who has studied bumblebees for many years, suggested that the problem would be alleviated if hortorum and subterraneus bumble bees could be established in the North Island. Visits To South Island

Mr Gurr made field trips to the South Island on behalf of the Grasslands Division, and, with the aid of Mr P. Clifford, of the division’s sub-station at Lincoln, succeeded in bringing 87 live queens of the hortorum species and 38 of subterraneus to Palmerston North where they were liberated in November and December.

Checks on the division’s red clover plots since the beginning of February have shown that workers and males of hortorum and workers of subterraneus are present. At least some of the queens of both species have established nests.

“It remains for the nest cycle to be completed, and the young queens to survive the winter, before we can be sure that the species have become established, but the prospects are promising,” said Professor Clark. Tf these bees establish themselves and increase as they have done in the South Island, the prospects for clover seed-setting in the North Island will be greatly enhanced.”

As far as is known, there are only four species of bumble-bees in New Zealand. The other two are Bombus terrestris and Bombus ruderatus. All four species were originally introduced from overseas as pollinators for crops, particularly red clover and lucerne, which cannot be pollinated satisfactorily by honey bees or native insects. The red clover flower carries its nectar in the base of a deep corolla tube in each floret. For effective pollination the insect must always visit the front of the florets, and only species with tongues long enough to reach the nectar will do this. Best Pollinators

Long-tongued bumble-bees such as ruderatus, hortorum or subterraneus are the best pollinators of this crop. Terrestris will effect some pollination of red clover, but, being a short-tongued species, it tends to take a short-cut to the nectar by puncturing the base of the floret. When it does this, pollination does not occur. Lucerne presents a different problem because it has a flower that “hits back.” The staminal column of the lucerne flower when tripped by

a visiting insect, springs up with considerable force and presses against the banner petal. In doing so, it strikes the insect a smart blow, and showers it with pollen. Successful pollination requires the body of an insect bearing pollen from another plant to be interposed between the staminal column and banner petal at the moment of tripping.

The terrestris bumble-bee is specially valuable as a lucerne pollinator because it is the only species in New Zealand which is prepared to stand the rap. Honey bees, and the longtongued bumble-bees, quickly learn to approach lucerne flowers cautiously from the side. Thus they seldom trip the flowers, and are not showered with pollen. Mr Gurr has found that seasonal availability of food can decisively influence the relative population of terrestris and ruderatus. Terrestris has only an incipient hibernation period in New Zealand conditions, and is generally active very early in spring, whereas ruderatus does not emerge from hibernation until later in spring. In districts where there is plenty of food for the bees in early spring, terrestris is already well established and is a stronger competitor for food when the ruderatus queens emerge in late spring. It has also the benefit of first choice of nesting sites. In areas where there is a dearth of food in early spiring and plenty in late spring, the position is reversed, and ruderatus tends to become the dominant species. The factors which determine the relative numbers ef terrestris and ruderatus in any area do not always favour the particular bee species Which will pollinate the crop farmers wish to grow there.