In Vitro Rearing Changes Social Task Performance and Physiology in Honeybees

Abstract

In vitro rearing of honeybee larvae is an established method that enables exact control and monitoring of developmental factors and allows controlled application of pesticides or pathogens. However, only a few studies have investigated how the rearing method itself affects the behavior of the resulting adult honeybees. We raised honeybees in vitro according to a standardized protocol: marking the emerging honeybees individually and inserting them into established colonies. Subsequently, we investigated the behavioral performance of nurse bees and foragers and quantified the physiological factors underlying the social organization. Adult honeybees raised in vitro differed from naturally reared honeybees in their probability of performing social tasks. Further, in vitro-reared bees foraged for a shorter duration in their life and performed fewer foraging trips. Nursing behavior appeared to be unaffected by rearing condition. Weight was also unaffected by rearing condition. Interestingly, juvenile hormone titers, which normally increase strongly around the time when a honeybee becomes a forager, were significantly lower in three- and four-week-old in vitro bees. The effects of the rearing environment on individual sucrose responsiveness and lipid levels were rather minor. These data suggest that larval rearing conditions can affect the task performance and physiology of adult bees despite equal weight, pointing to an important role of the colony environment for these factors. Our observations of behavior and metabolic pathways offer important novel insight into how the rearing environment affects adult honeybees.

Honeybees are buffered against undernourishment during larval stages

“…We expected severe effects of undernourishment on adult honeybees as it has been shown multiple times that poor nutrition can severely affect honeybee colonies, especially during autumn when the flowers stop blooming ( 57 – 59 ). As a reference point for undernourishment we used the standard artificial rearing diet which is known to be sufficient for honeybee rearing ( 30 – 33 , 36 ). Earlier experiments showed effects of larval undernourishment on adult morphology, with undernourished larvae having slightly smaller thoraces and heads than honeybees reared under normal diet ( 37 ).…”

“…To acquire honeybee larvae, the queens were caged for 24h. After three days the newly emerged honeybee larvae were transferred into the laboratory and reared in-vitro according to a standardized protocol ( 30 – 36 ). Three groups of honeybees were reared under different diets [ Table 1 : 150 µl (“undernourished”), 160 µl (“normal diet”) and 180 µl (“overfed”)] based on data of ( 37 ).…”

“…On day 1, honeybees received diet A, on day 3 they received diet B and on the following days honeybees received diet C. Food quality did not differ between the treatments, just the quantity differed. Honeybees were reared according to ( 36 ). In short, age-controlled larvae were individually grafted and placed into small plastic cups (Weisel cups, Heinrich Holtermann KG, Brockel, Germany).…”

“…For the foraging behavior observations, honeybees were treated identically as before. However, instead of colored number plates, radio-frequency identification (RFID) tags (mic3-TAG 64bit read only, carrier frequency: 13.56 MHz, microsensys GmbH, Erfurt, Germany) were used to mark the emerging honeybees ( 36 , 39 ). After the drying period in the incubator, the cages were placed into four six-frame queen-right mini plus colonies (small, standardized colonies containing approx.…”

“…On the second day of the experiment and 7, 14 and 21 days afterwards, five honeybees were removed from each colony and treatment to perform further analyses. First, honeybees were immobilized on ice and weighted ( 36 ). Then they were fixed in metal tubes and fed until satiation using 30% sugar water ( 40 , 41 ).…”