Introduction

1. 9 19 15 Phosphorus a possible mechanism for faster growth in Africanized honey bees Dina L. Grayson and Jennifer H. Fewell School of Life Sciences, Arizona State University Tempe, AZ, 85287-4601 Introduction Faster growth and reproduction contribute to the success of several invasive species, including the Africanized honey bee. The Africanized honey bee has out-competed European honey bees throughout much of the Americas due in part to their faster colony growth. One component of faster colony growth is faster development times of African worker bees. African worker bees develop to a size of approximately 65 mg in 19 days, while European workers develop to a size of 75-96 mg in 21 days. These differences in size and development time persist regardless of whether the bees are raised in separate or communal hive environments. Thus, the specific growth rate (change in mass over time normalized for mass) of an Africanized bee is approximately 0.053 while that for a European bee is ~ 0.048. Recently, specific growth rate was found to correlate positively with phosphorus content in some aquatic invertebrates. Since ribosomal RNA is phosphorus-rich relative to other cellular components in small organisms, it was hypothesized that organisms with faster specific growth rates are increasing their number of phosphorus-rich ribosomes in order to increase their rate of protein synthesis. Therefore, organisms with faster growth rates should have higher phosphorus contents. We tested this hypothesis using Africanized and European honey bees. Discussion Our results indicate that Africanized honey bee eggs are similar in phosphorus content to European eggs. However, Africanized larvae tend to have more phosphorus than Europeans at both 7 and 10 days. These data are consistent with the hypothesis that faster larval growth and development of Africanized workers is linked to increased amounts protein synthesis and phosphorus-rich ribosomal RNA. Our results also show some interesting trends in phosphorus content throughout development. The similar phosphorus content of Africanized and European eggs indicates that differences at the larval stage are most likely due to differences in larval food consumption or retention and not initial biases. Additionally, the significance of the date in affecting egg phosphorus content may indicate that changes in the nutritional quality of food being fed to the queen are important. The other major change with development was the sudden drop in phosphorus content of larvae between larvae at age 7-days and those at age 10-days. Larvae are actively growing and being fed at day 7, but stop feeding and begin to pupate around day 10. Therefore, the drop in phosphorus content between ages 7 and 10 is consistent with the hypothesis that larvae need more phosphorus-rich ribosomes during periods of intensive growth. The data presented here are preliminary, but they show the start of interesting trends both between African and European honey bees and throughout worker bee development. Although more work is needed in order to more fully characterize the relationship between phosphorus and growth, the data presented here indicate this work could increase our understanding of the mechanisms that lead to faster growth and overall success of the Africanized honey bee. Results Do Africanized honey bee eggs contain more phosphorus than European eggs? NO Figure 1. Mean ± SEM percent of phosphorus by dry weight of eggs laid by one Africanized queen at two dates (a and b) and one European queen. Nested ANOVA found date was significant p = 0.0002, but bee type (African or European) was not significant (p = 0.45) Do Africanized worker larvae 7-days post egg laying contain more phosphorus than Europeans? YES 16 13 30 20 22 • Methods • Colony type (Africanized or European) was determined based on analyses of mitochondrial DNA of workers. • Queens were caged on empty comb for 24 hours. • Samples were collected the day after the queen was caged (eggs) and again on day 7 and 10 (larvae). • Samples were dried at 60 ºC for 3 days. • Samples from days 7 and 10 were homogenized by use of a ball mill. • Two sub-samples of each homogenized larvae and one sample of each egg were analyzed for phosphorus content. • Phosphorus content of samples way assayed using a standard ascorbate-reduced moybendum-blue method after digestion with potassium persulfate. Figure 2. Mean ± SEM percent of phosphorus by dry weight of larvae from three Africanized colonies and two European colonies. Nested ANOVA found both bee type (p = .0030) and colony nested within bee type (p < 0.0001) were significant. Do Africanized worker larvae 10-days post egg laying contain more phosphorus than Europeans? YES 10 10 Acknowledgements The authors would like to thank Matthew Harwood, Dr. Jon F. Harrison, Marcia Kyle, Dr. James Elser, and the USDA Carl Hayden Bee Research Center. Figure 3. Mean ± SEM percent of phosphorus by dry weight of larvae from one Africanized and one European colony. One-factor ANOVA found significantly differences between bee types (p = .0008).