ARBEITSGEMEINSCHAFT DER INSTITUTE FÜR ... - HAL - INRIA

zeit eingetreten sein. Wahrscheinlich sind die Ammenbienen nicht in der Lage,
die Brut erfolgreich zu pflegen. Messungen der Hypopharynxdrüsen bestätigen
diese Annahme. Die Acini der Bienen aus den Versuchsgruppen 0.4 ppm und
0.2 ppm sind signifikant kleiner als die der Kontrolle. Auch die Bautätigkeit wird
durch die subletalen Dosen Dimethoat beeinträchtigt. So produzierten Bienen, die
über 44 Tage mit 0.2 ppm Dimethoat gefüttert wurden und anschließend für
8 Tage in kleinen Kästchen bei 35 1- 1 °C bauten, 19,6 % weniger Wachs als
bewirkten noch keine ver-
die Kontrollen. Kurzfristige Fütterungen mit 0.2 ppm
minderte Wachsproduktion.
SUMMARY
Changes in honey bee workers after feeding them with sublethal doses
of dimethoate
When plants are treated with systemic plant-protective agents, residues may be
found in the nectar. The residue level of dimethoate depends on the timing of
treatment of the blossoms and sampling after the onset of blooming. This level
has been measured by FIEDLER (1984). The concentrations found in adult bees
are sublethal. I investigated which changes can be found in bee colonies or
individual bees after feeding them with pure dimethoate in sublethal doses.
After bees were fed with sugar-paste with concentrations of 0.4 ppm and
0.2 ppm dimethoate, the following results were observed for the 0.4 ppm group.
The queen bees discontinued laying eggs within 11 to 21 days. From the eggs
laid in one colony, only 76 bees reached the pupal stage. These developed without
appreciable loss into adult bees. After interchanging the contaminated food,
queen bees began laying eggs again. A queen bee that was exposed to the poison
for over 42 days, after a recovery period of 14 days, laid eggs again, which
developed normally. In the group fed 0.2 ppm, the queen bees laid eggs during
the entire experiment equal to the control group with untreated food, but significantly
fewer larvae developed compared to the control. Since the embryonic
development is not impaired, the breeding loss must have occurred during the
larval stage. The nurse bees were probably not able to care for the brood successfully.
Measurements of hypopharyngeal glands confirmed this suggestion. The
bees’ acini from the 0.4 ppm and 0.2 ppm groups were significantly smaller than
those of the control group. Also, nest building activities were impaired by
sublethal doses of dimethoate. Bees which were fed with 0.2 ppm dimethoate
for 44 days and then allowed to build nests in small boxes for 8 days at 35 °C
produced 19.6 % less wax than the control. Short-term feeding with 0.2 ppm
resulted in no decrease in wax production.