Norbert Hrassnigg

Adaptation of hypopharyngeal gland development to the brood status of honeybee (Apis mellifera L.) colonies

We studied pollen consumption, head weight, hypopharyngeal gland (HPG) acini diameter, and protein synthesis and transfer in honeybee workers reared in colonies with normal and with decreasing amounts of brood. We found that head fresh weight is correlated with size of the glands and that pollen consumption is positively correlated with gland development. An effect of brood on size of the glands could be confirmed, but was not as profound as in previous studies. Similarly, no difference in the amount of protein synthesized or transferred in workers living under the two brood conditions was found. We suspect this is due to the fact that HPGs also supply food to young bees and in our study young bees were always present while in previous studies, colonies often lacked both brood and young bees.

The influence of brood on the pollen consumption of worker bees (Apis mellifera L.).

(1) In midgut dry weight (tissue plus contents) of worker bees we found a representative parameter for pollen consumption. Midguts of bees of successive ages were analyzed and correlated with various parameters. The relative proportions of sugar, protein and water were either constant or negatively correlated with midgut weight. Only the relative pollen weight (percent of midgut dry weight) increased. (2) To investigate the influence of different levels of brood on pollen consumption of individual bees, midgut dry weights from 2 normally breeding control colonies and 2 brood-reduced experimental colonies were analyzed. In bees from control colonies the pollen consumption increased up to the nursing age (3-10d), remained on an elevated level in middle-aged-bees (10-18d) and decreased relatively sharply towards the foraging ages (>21d). When queens were caged in the experimental colonies, the following decline of brood cells affected the consumption of pollen differently. After 6 days of caging, with a reduction of open brood only, no effect was seen. After 15 days, and even more pronounced after 23 days when no brood was present, the pollen consumption in young and middle-aged (10, 14, 18d) worker bees was significantly reduced, while it was clearly elevated in older bees. We discuss pollen consumption as an adaptation to reduced necessity to nurse brood in young and middle-aged bees, and to enhance life span in older animals.

Free amino acids in the haemolymph of honey bee queens(Apis mellifera L.)

Summary. In queen honey bees the free amino acid content in the haemolymph clearly depends on the physiological function and social environment of the individual. While in drones and workers the content of free amino acids increases after emergence until it reaches a peak in 5-day-old animals and decreases afterwards, the amino acid content in queens reaches its highest level (>60 nmol/μl haemolymph) with the onset of egg laying (10 d of age). This level is about 2.5 times more than the highest level found in workers. Queens maintain this high level also when they are older (>30 d) and continue to lay eggs in average colonies. As in drones and workers, in queens the predominant amino acid is proline, which accounts for more than 50% of the total content of free amino acids in egg-laying individuals. When 10-day-old queens are prevented from mating and do not lay eggs, their amino acid content is significantly lower compared to laying queens of the same age. Also the social environment influences the contents of free amino acids in queens. When virgin queens were kept for 6 days with 20 worker bees and sufficient honey and pollen in an incubator, they had significantly lower concentrations of amino acids than virgin queens living for the same period with about 8000 workers in a colony. Most probably, the high amino acid concentration in the haemolymph is the basis for the high protein synthesis activity of laying queens.

Does Patriline Composition Change over a Honey Bee Queen’s Lifetime?

A honey bee queen mates with a number of drones a few days after she emerges as an adult. Spermatozoa of different drones are stored in her spermatheca and used for the rest of the queen’s life to fertilize eggs. Sperm usage is thought to be random, so that the patriline distribution within a honey bee colony would remain constant over time. In this study we assigned the progeny of a naturally mated honey bee queen to patrilines using microsatellite markers at the queen’s age of two, three and four years. No significant changes in patriline distribution occurred within each of two foraging seasons, with samples taken one and five months apart, respectively. Overall and pair-wise comparisons between the three analyzed years reached significant levels. Over the three-year period we found a trend for patrilines to become more equally represented with time. It is important to note that this study was performed with a single queen, and thus individual and population variation in sperm usage patterns must be assessed. We discuss long-term changes in patriline composition due to mixing processes in the queen’s spermatheca, following incomplete mixing of different drones’ sperm after mating.

Predator-prey interaction between drones of Apis mellifera carnica and insectivorous birds

Large offers of food usually do not remain unexploited in nature. For that reason several mechanisms have evolved to counteract predation, such as congregating in masses or producing a repellent substance. We investigated whether drones are preyed upon in any specific way by two swallow species, Hirundo rustica or Delichon urbica, in their drone congregation areas. Our results clearly showed that the birds preyed upon drones extremely sporadically and not in a specific way. Hence, the results have decisive consequences for apiculture, especially for the evolution of drone accumulation in congregation areas.ZusammenfassungGroße Futterangebote bleiben in der Natur für gewöhnlich nicht ungenützt (Bryant, 1973). Aus diesem Grund haben Beutetiere im Laufe der Evolution verschiedene Strategien gegen Räuber entwickelt, wie zum Beispiel das kurzzeitige Vorkommen in Massen, sodass immer ausreichend viele Individuen überleben (z.B. Termiten; Abe Takuya, 2000), oder das Produzieren von Abwehrsubstanzen (Witz, 1990; Pasteeis et al., 1983). Was die Drohnen der Honigbienen betrifft, ist bis jetzt noch keine Abwehrsubstanz nachgewiesen worden. Im Gegenteil, diese weisen sogar einen außerordentlich hohen Anteil an Protein auf (Hrassnigg und Crailsheim, 2005), was nahe legt, dass sie eine ideale Beutequelle für insektenfressende Vögel wie zum Beispiel Schwalben wären. Außerdem ist das Vorkommen der Drohnen an ihren Plätzen sowohl zeitlich als auch örtlich leicht vorhersagbar (Ruttner, 1966).Ziel der Untersuchungen war es festzustellen, ob Drohnen von den zwei Schwalbenarten Hirundo rustica oder Delichon urbica bzw. anderen Vögelarten gezielt auf ihren Sammelplätzen bejagt werden.Um dieses Verhalten zu quantifizieren, maßen wir die Aktivität der Schwalben drei Mal pro Tag/Platz, genauer gesagt in der Zeit von 10.00–11.00 h am Vormittag, 13.55–14.55 h und 15.05–16.05 h am frühen Nachmittag und 18.00–19.00 h am frühen Abend und verglichen die Messwerte der Drohnensammelplätzen zur „Drohnenzeit“ (i.e. früher Nachmittag) mit denen, welche wir zur gleichen Zeit an den Vergleichsplätzen erhielten, und mit den Messwerten, welche wir an den Drohnensammelplätzen in der Früh und am frühen Abend erhielten, wo Drohnen noch nicht bzw. nicht mehr anwesend waren. Zusätzlich ermittelten wir auch die Stärke des Drohnenvorkommens, um zu sehen, ob ein Zusammenhang zwischen der Drohnenanzahl und der Aktivität der zwei Schwalbenarten besteht. Außerdem nahmen wir Proben von Schwalbenexkrementen und untersuchten diese nach unverdauten Drohnenteilen als Beweis für deren Bejagung.Zusammenfassend kann gesagt werden, dass die Aktivität der Schwalben an Drohnensammelplätzen, wenn Drohnen vorhanden sind, nicht höher war und, dass es auch keinen Zusammenhang zwischen der Intensität ihrer Aktivität und der Anzahl der zur selben Zeit vorhandenen Drohnen gab. Wir fanden zwar einige wenige Drohnenteile in den Exkrementen der Rauchschwalben, welche jedoch, verglichen mit dem Gesamtanteil an erbeuteten Insekten, vernachlässigbar waren.Unsere Resultate zeigen daher, dass Rauchschwalben selten, Mehlschwalben vermutlich nie Drohnen fressen. Königinnenverluste können daher nicht mehr auf Vogelfraß zurückgeführt werden, zumindest in Gegenden wo keine Bienenfresser oder Blauracken vorkommen. Unser Ergebnis könnte auch erklären, warum Drohnen (Winston, 1987) im Gegensatz zu den Männchen vieler anderer einmalig schwärmender Insektenarten (Hölldobler and Wilson, 1990; Abe Takuya, 2000) an jedem warmen und sonnigen Tag von April bis September in Ansammlungen vorkommen können.