Metabolic activity of haemocytes compared with the haemocyte system of bees fed with pollen.

In honeybees fed sugar only, there was a smaller percentage of other types of haemo- cytes and an increase of granular haemocytes, which suggest a decrease in the differentiation of haemocytes and a possible mobilization of older granular haemocytes which may act as storage cells in the insect.

The above follows from the Fisher LSD pro- cedure carried out for selected average pairs. Regarding the total number of haemocytes (THC), significant differences were found between the proteinless diet and the diet with pollen substitute. For the metabolic activity of haemocytes (NBT test) and for the percentage of granular haemocytes and plasmatocytes, sig- nificant differences were found between all feeding groups. For the ‘other’ category of haemocytes, no significant differences between the diets were found.

DISCUSSION

The haemocyte system from standard bee colonies and from incubator-raised bees with proteinaceous diet based on pollen substitute showed a similar picture with similar propor- tions of each type of haemocytes. But the total number of haemocytes in bees fed on pollen substitute was lower and the metabolitic activ- ity of these haemocytes was less in compari- son to bees raised in bee colonies in the open. In the haemolymph of bees fed on non-pro- teinaceous diet, there was a greater proportion of granular haemocytes and a smaller propor- tion of plasmatocytes in comparison to the haemolymph of bees from standard bee colo- nies. Furthermore, in the group without pro- tein in their diet, there was a greater total number of haemocytes and a smaller number of metabolically active haemocytes when compared with the haemocyte system of the bees raised in standard bee colonies. In the haemolymph of incubator-raised bees fed on pollen, the total number of haemocytes was similar to that of bees raised in standard colo- nies in the open. The metabolic activity of haemocytes of workers fed pollen in the incu- bator was also more similar to that of bees raised in standard colonies compared to that of

the worker bees fed other diets. In the haemo- lymph system of incubator-raised bees fed on pollen, there was a higher proportion of gran- ular haemocytes and of haemocytes of the ‘other’ category. There was also a smaller pro- portion of plasmatocytes in comparison to the haemolymph of bees raised in standard colo- nies. The high value of the standard deviation (s.d. = 8984) in the total number of haemo- cytes in the experimental group fed on pollen might have resulted from the botanical diver- sity of the pollen used in the successive years of experiment. There were few significant dif- ferences in the haemolymph of incubator- raised bees fed with natural pollen versus pol- len substitute.

The results show that feeding bees with a non-proteinaceous diet may activate the mech- anism compensating for a lack of protein in the haemolymph of the bee. The total number of haemocytes increased, as did the proportion of older haemocytes which may be nutrient cells, while there were fewer young haemocytes as described by other authors as plasmatocytes or prohaemocytes (Wienands et al., 1987; Wienands and Madel, 1988; van Steenkiste, 1988; Papadopoulou-Karabela et al., 1993). Our results are in agreement with those of pre- vious studies that found that plasmatocytes are the most numerous cells in haemolymph of young honeybee from free-flying colonies (Jędruszuk, 1998a,1998b, 1998c). They also confirm observations made earlier by Wienands et al. (1987) and van Steenkiste (1988). However, examination of plasmato- cytes only may not be sensitive enough, as the next consequence of a lack of protein in the diet was a large decrease in the proportion of metabolically active cells, which suggests a reduced ability to phagocytose. Gliński and Klimont (1987a, 1987b) observed a decrease in total haemocyte count, but no change in the metabolic activity of haemocytes in the haemolymph of honeybees infested with the mite Varroa destructor. The present experi- ment shows that a lack of protein in the diet can cause greater disturbances in the function- ing of the cellular system of the haemolymph than parasitism by V. destructor. So far, the problems referring to the diversity of the honey bee haemocytes have not been dis- cussed in any scientific sources, therefore, the

Influence of diet on honeybee haemocytes 101

Date: 2015-12-17; view: 638