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insects. Adv. Ins. Physiol. 2, 247-336.

Effect of Temperature on the Behaviour and Pollinating Efficiency of Honeybees on Winter Rape Flowers

By P. BENEDEK~ and J. PRENNER~

With 2 Figures

Abstract

Decided correlation could be established between flower visiting speed of honeybees and temperature (r = 0.823) as well as between the number of flowers visited per plant and the temperature (r = - 0.504) respectively. The flower visiting speed of honeybees increases with the rise in temperature and simultaneously the number of flowers visited per plant drops. Possibilities of cross-pollination are, therefore, on the rise in an increased degree when the temperature goes up.

Introduction

Several observations have already been made concerning the flower visiting speed of honeybees on winter rape (Brassica napus L.). The number of flower visits per minute was found to be 9.7 by BELOZEROVA (1960), 10 by RAD- CHENKO (1964) and 12 by PETKOV (1963). FREE and NUTTALL (1968) recor- ded that honeybees spent 4.1 sec per flowers which is equivalent to 14 flower visits per minute. PETKOV (1963) suggested that the flower visiting speed may be connected with the temperature. For studying this problem some observa- tions were made in 1971 on a 31 hectare winter rape field in the vicinity of Kim, Western Hungary.

Method

The flowering on the winter rape field started on 22nd April. On 24rh April 46 honeybee colonies in 24-frame hives had been moved to the field. On 26th April, llrh, 13th and 18th May respectively a total of 65 honeybees were observed as long as possible in sunny weather

Forecasting Centre at Central Plant Protection and Quarantine Laboratory of Ministry Agriculture and Food, Budapest 11. Herman Ott6 u. 15. '' District Plant Protection Station, Tanakajd, Hungary.

2. ang. Ent. 71 (19721, 120-124 0 1972 Verlag Paul Parey , H a m b u r g u n d Berlin

Behaviour and Pollinating Efficiency of Honeybees 121

at each occasion between 12 m. and 1 p.m. The time of the observation, the number of visited flowers and inflorescences respectively, furthermore, the temperature and the wind velocity were recorded. The wind speed, however, having been similar during all obser- vation (1 B O ) , was neglected in the analysis of data.

At a distance of 150, 300 and 600 m respectively off the field-margin, facing the row of hives, the density of honeybees was observed in 100 m long X 1 m wide plots of the flowering crop on 5 different days on each occasion between 12 m. and 2 p.m.

Results

All observed honeybees gathered both nectar and pollen. Individuals gather- ing exclusively nectar or pollen respectively could not be found. Observing bees just arriving from the hives it was established that during the first minu- tes of the trip the bees gathered mainly nectar then, by and by, took to gathering pollen with increasing intensity.

The 65 observed individuals visited collectively 2845 flowers in 286.6 minutes. Means of flower visits per minute and number of visited flowers per plant calculated from the data obtained in different days are given in Table 1 .

Table 1

Flower visiting speed and number of flowers visited per plant by honeybees a t different temperatures (means and their standard deviations are given)

Total time No' Of flowers No. of bees of bees'

observed obseryed activitv

visited Date Temperature No' Of .flower VlSLtS per minute per plant QC

~~~

1 l t h May 19 6.96 k 0.61 1.68 k 0.06 12 40.5 min. 23rd April 20 8.52 k 0.64 1.76 k 0.11 11 61.0 min. 13th May 22 10.42 2 0.58 1.36 k 0.03 25 122.0 min. 18th May 26 15.47 2 0.66 1.30 f 0.03 17 63.1 min.

It was possible to observe the bees for a mean of 4.4 minutes. The bees spent 6 seconds on one flower. The individuals visited a mean of 9.93 k 0,49 flowers per minute and they visited a mean of 1.46 f 0.02 flowers in one inflorescence. In the field the inflorescence of neighbouring plants entangled. At the same time the bees are usually flying regularly more than 1-2 dozens of centimetres before alighting on another inflorescence. Thus, it occurred very seldom that a bee should have settled repeatedly on another inflores- cence of the same plant. One may, therefore, speak of plants instead of inflorescences.

One of the individuals, however, could be observed for as long as 35.5 minutes. This must have been her complete gathering trip. This bee had arrived from the direction of hives and visited 342 flowers on 186 plants in a 5 X 5 metre area. Then flew 1 metre above the flowers, made some cir- cular orientation flights and, ultimately, took straight to the hives. During the gathering trip she rested three times for about 30-40 seconds brushing the pollen from her body into the corbiculae. This observation confirms RADCHENKO'S (1964) statement that in winter rape bees visit about 300 flowers per trip.

122 P. Benedek and 1. Prenner

A decided correlation could be established between flower visiting speed of honeybees and temperature (r = 0.823, p < 0.001) as well as between the number of flowers visited per plant and the temperature respectively (r = - 0.504, p < 0.001). Parallel with the rising temperature the flower visiting speed substantially increases (Fig. 1) and a t the same time the num- ber of flowers visited in the same plant drops (Fig. 2).

C" 1 8

20 22 2 L 26 18 20 2 2 2L 26

Fig . 1 (lef2). Effect of temperature on the flower visiting speed of honeybees on winter rape - F i g . 2 (right). Effect of temperature on the number of flowers visited per plant by

honeybees on winter rape

Table 2

Honeybee density in different days (means and their standard deviations)

18

Date Temperature Clouds Wind O C per cent B O

Stage of flowering

No. of honey- bees on 100 sq.

metre plots

27th April 17 10 1 start of flowering 44 f 1.6 5 t h May 17 80 1 mass flowering 47 f 4.2 7th May 23 10 1 mass flowering 421 k 27.5

11thMay 19 10 1 mass flowering 306 ? 6.1 1 8 t h May 26 0 1 end of flowering 329 f 24.8

It was impossible to reveal reliable correlation between the density of honeybees and temperature. However, based on the data in Table 2, it may be concluded that the temperature has a substantial influence on the density of bees because at higher temperatures more honeybees visited the 100 sq. metre plots.

Discussion and Conclusions

Our findings may explain the differences in the results of earlier observations of flower visiting speed of honeybees on winter rape. Namely, the individual workers may have carried out their observations at different temperatures.

Considering the above trends it may be concluded that the pollinating

Behaviour and Pollinating Efficiency of Honeybees 123

efficiency of honeybees is significantly higher a t high than at lower tempera- tures. The significant increase of the flower visiting speed causes the increase in pollinating efficiency, however, simultaneously there is substantial drop in the number of flowers visited in a plant as well. It seems likely that at higher temperatures honeybees carry pollen to almost each flower from another plant, wherefore, the possibilities of cross-pollination between plants may significantly increase.

PETKOV (1963) presumed that the flower visiting speed may be in connec- tion with the nectar secretion of the plants. Though it was established by BELOZEROVA (1960) and RADCHENKO (1964) that the intensity in nectar secretion is greatly different during the subsequent stages of flowering, according to FREE and NUTTALL (1968) the time spent by honeybees per flower showed no trend with the stage of the flowering of the crop. The increase in the flower visiting speed seems to be primarily concerned with the temperature which has a direct effect on the movement of the bees.

However, the number of flowers visited per plant is presumably corre- lated with the density of honeybees and with the nectar content of the flow- ers as well apart from the temperature. In the case of great density the bees accidentally may directly disturb each other. At the same time, at great honeybee density the frequent sucking of nectar by the bees may cause in- creasing competition among honeybees. MEYERHOFF (1958) pointed out that bees in flight are unable to distinguish flowers with empty and full nectaries respectively, but they learn in a short time that i t is aimless to try another flower where one is empty. Increasing competition or little nectar secretion will, therefore, decrease the number of flower visits per plant. However, the effect of these factors needs further investigations.

In lucerne fields SEDIVY and OBRTEL (1968) observed definite correlation between the number of flowers visited per minute and the temperature, fur- thermore, between flower visiting speed and intensity of illumination in honeybees and the females of Rhophites canus EV. respectively. Therefore, it seems to be likely that the pollinating efficiency of bees is in correlation with the temperature and/or with the influence of other mentioned factors in several crops. This indicates the necessity of similar investigations in other crops also relating to the factors influencing behaviour of honeybees on flowers.

Acknowledgements

Me are grateful to Miss P. PISSINGER for her help with the observations and to Mr. J. SURJAN and Mr. F. NAGY for the translation of Russian and Bulgarian sources.

Zusammenfassung

AhtiwitLit tiizd Bestaubungsel-fektivitat der Honigbicne an Winterrapsbiziten, in Abhangig- keit won der Temperatur

Bei TeniperaturerhGhung ninimt die Geschwindigkeit des Bliitenbesuchs zu und gleichzeitig nimmt die Zahl der je Pflanze aufgesuchten Bliiten ab. So erhoht sich die Moglichkeit der Freindbestaubung mit Zunahme der Temperatur in gesteigertem Mafie. Die Bestaubungs- effcktivitat der Honigbiene diirfie wohl auch bei zahlreichen anderen Pflanzenarten mit d c r Temperatur zusamnienhingen.

124 P. Benedek and J . Prenner

References

BELOZEROVA, E. I., 1960: Bees increase the seed crop from winter rape. Pchelovodstvo 9,

FREE, J. B.; NUTTALL, P. M., 1968: The pollination of oilseed rape (Brassica napus) and

MEYERHOFF, G., 1958: Zum Sammelverhalten der Biene im Raps. Leipziger Bienenztg. 72,

PETKOV, V., 1963: Nectar and honey production of winter rape. Izv. Inst. Ovoshcharstvo

RADCHENKO, T. G., 1964: The influence of pollination on the crop and the quality of seed

SEDIVY, J.; OBRTEL, R., 1968 : Observations on bees pollinating lucerne in Czechoslovakia

38-40.

the behaviour of bees on the crop. J. agric. Sci. 71, 91-94.

164-165.

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(Hym., Apidae). 2. ang. Ent. 62, 121-138.

Aus d e n Staatlicben Weinbau-Institut, Freiburg i. Brg.

Das Vorkommen von Milben aus der Familie Tydeidae (Acari) an Reben

VI. Beitrag uber Untersuchungen zur Faunistik und Biologie der Milben (Acari) an Kulturreben (Vitis spec.)

Von GUNTER SCHRUFT

M i t 6 Abbildungen

Abstract

Occurrence of mites from the family Tydeidae (Acari) on vines ( V i h spec.). VI. Studies on faunistic and biology of Acari on V i h spec. The species of Tydeidae (Acari), found as yet on vines (Vitis spec.) has been summarized. The morphological data of adults and the characteristics of the immature stages of two species (Tydeus goetzi and Pronematus staerki) are described, indicating a clear picture from the development of the tydeids. Little is know about the importance of the tydeids for the viticulture. There are predators, feeding on gall-mites; other tydeids are phytophagous, damaging the leaf of vines.

I. Einleitung

Wahrend unserer mehrjahrigen Untersuchungen zur Faunistik und Biologie der Milben an Reben (SCHRUFT 1966, 1967, 1969) fanden wir auch Indivi- duen aus der Familie Tydeidae.

Uber das Vorkommen von Tydeiden an Reben ist bisher nur wenig be- kannt geworden. GUNTHART (1 957) berichtet uber undeterminierte Staubmil- ben der Familie Tydeidae, die in der West- und Sud-Schweiz fast immer in kleinerer oder groi3erer Zahl auf Rebblattern zu finden waren, ohne dai3 ein

2. ang. Ent. 71 (19721, l2+-135 0 1972 Verlag Paul Parey , H a m b u r g u n d Berlin