Q19 — Heat-Balling Honeybee Defense Against Hornets

Theoretical B Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license

Honeybees like Apis cerana (Ac) and Apis mellifera (Am) defend against hornets (Vespa velutina, Vv) by forming a 44°C heat ball and stinging. The effects of heat (25°C or 44°C in thermostatic conditions) and stings from both species on hornet survival were studied. A mutant A. mellifera colony (Amdef) can generate heat but cannot sting and in all other aspects is similar to wild-type ones. Scientists also examined the body mass, venom mass, and stinger length of Ac, Am, and Vv. The figures below show data for wild-type bees.

Panel A: three survival curves (no sting, Ac single sting, Am single sting), each comparing 25°C vs. 44°C hornet survival over 180 minutes. Panel B: three bar charts comparing body mass, venom mass, and stinger length across Ac, Am, and Vv. Figure 1. A Graphs show the proportion of surviving hornets over time. p < 0.05 indicates statistical significance. B Body mass, venom mass, and stinger length for three species.

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. Venom mass is 2.6-2.8% of V. velutina's body mass.

B. Amdef bees can't kill any attacking V. velutina.

C. Amdef bees kill hornets as efficiently as the A. cerana species.

D. Over 3 hours at 44°C, the same number of A. cerana bees can kill more hornets than A. mellifera bees.

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Question reproduced from IBO 2024, Theoretical Exam Part B, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF