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Gentiana pneumonanihe

Bumblebees were the main pollinators - 62.1% from all visitors (Kozuharova,

2004). Field observations on the bumblebees behaviour revealed high flower constancy.

The population in the Western Stara Planina Mts was pollinated almost exclusively by

male bumblebees

Bombus agrorum

feeding on nectar (Table 1). In the population

growing in Ljulin Mts. nectar collecting workers

B. horiorum

visited the flowers of this

gentian (Table 1). Only two workers

B. horiorum

had full pollen baskets to be analyzed.

The high flower constancy of bumblebees workers observed in the fields

correlated with a high percentage of

Gentiana-

type pollen found in their pollen baskets

(mean - 98.2%. min -- 96.7% max ~ 99,6%, Table 7). Their “minors" were 1-4 plant

species (Table 8). The presence of pollen from dish-bowl blossoms Asteraceae was

significantly poorer compared to the abundance of these plants in the area. On the

contrast the “gullet" type - e. g. Lamiaceac were presented much better compared to the

flowering plants (Tables 5, 4a),

Gentiana

pollen quantity was high in the baskets of both

workers (Tables 7 and 8).

Gentiana cruciala

Bumblebee visits were 18.9% of all insect visits, Bumblebees were the main

pollinators together with

Halictus

bees (K ozuharova, A nchev 2001). Most numerous

were workers

Bombus horiorum -

73.2% of all bumblebees (Table 1). They collected

nectar. In 1990 and 1991 the pollen baskets of Я.

horiorum

were empty. In 1994 some

horiorum

workers carried full pollen baskets. The high flower constancy of

B. hortorum

workers observed in the fields correlated with a high percentage of

Gentiana-xype

pollen

found in their pollen baskets (mean = 64,7%. min - 4.3% max = 99.4%). Their “minors"

were 1-7 plant species abundant in the area (Tables 7, 8). The “dish-bowl" blossoms

were presented not adequately to the abundance of these types in the area (Tables 6, 6a,

Fig. 3), e. g. the cornucopian taxa

Heiianthemum

and

Hypericum

occurred in the pollen

baskets rarely, while Apiaceae and especially Brassicaceae were presented by pollen

better than in the area. On the contrast, Asteraceae pollen was significantly presented -

83.3% of the pollen loads contained 1-3 pollen types from this family, though these were

not the most abundant plants in the area. The quantity of

Gentiana

pollen was high:

Bombus horiorum (n =

5, mean ” 76.8%, min ~ 56.9% max - 99.5%). The pollen loads

of the worker

B. pomorum

contained a mixture of different pollen types and

Geniiana-

type pollen grains were comparatively few. The presence of

Aconitum~iype

pollen there

indicates a unde foraging perimeter as these plants did not bloom in the neighbourhood.

CONCLUSION

I .

Flower constancy correlated to the bumblebee species, caste and individuals,

There was not obvious pattern of correlation between the caste and the flower

constancy. The flower constancy varied between the individuals of a certain bumblebee

species - some workers and queens did not visit other plants. Others had pollen from

several (up to 9) plant species (Table 8). That was especially true for die workers Я

pratorum. Bombus pyfenaeus

tended to be comparatively most constant, The flower

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