Matsuyama, Hinako

Ono, Masato

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Hinako Matsuyama and Masato Ono  Graduate School of Agriculture, Tamagawa University Tokyo 194-8610, JAPAN Methods  Experiment 1.  Tendency of takeover behavior by post-hibernation queen  We checked if post-hibernation queen preferred an orphan nest or just an empty cavity as her nesting site.  Two orphan nests (number of cocoons 5-10) and two empty boxes put into a larger observation box, then a post-hibernation queen searching for a suitable nesting site was installed (Fig. 1). We observed which nest was chosen by the queen.                 Fig. 1    Design of experiment 1 Orphan nest Empty box 0 5 10 15 Orphan nest Empty box Number of queens Fig. 3   Preference of post-hibernation queen for orphan nest             or empty box as nesting site (Experiment 1 ) Experiment 2.  Impact of nest takeover on colony development  We checked if reproductive fitness increased with the nest takeover. The foundress queen was removed from her initial nest, and a fresh post-hibernation queen was installed in the nest (Fig. 2). Then we reared the artificially taken over nest in the laboratory. The number of reproductives (new queens and males) produced from the takeover nests and non-takeover nests (as control) were compared to clarify the adaptive significance.                 Table 1    Number of days workers and reproductives (males and                  new queen) required for emergence (Experiment 2)                                                                                                     mean±SD Fig. 5  Comparison of  final productivity between             the  non-takeover (n=6) and  takeover (n=6)             colonies (Experiment 2)        Fig. 4   Comparison of increase in number of egg cups between                  non-takeover (n=10) and takeover queens (n=6)                 (Experiment 2).  0 10 20 30 40 50 0 7 14 21 28 35 42 Number of egg cups days  non-takeover queen  takeover queen Worker Male New queen Non-takeover queen 31.2±4.5 78.8±12.7 100.0±6.2 Takeover queen 24.7±2.4 69.8±10.3 61.2±14.1 Initial nest (A) founded by queen A  A A Initial nest (A) taken over by queen B artificially  A B exchange A B Fig. 2   Design of experiment 2  Conclusions • Post-hibernation queens prefer orphan nests as nesting sites and the nest takeover by the queens occurs easily in laboratory. • Ratio of increase in number of egg cups was faster in the takeover nest than non-takeover nest, suggesting brood elicit oviposition by takeover queen. • Emergence of males and new queen from takeover nest was earlier and number of reproductives was higher than non- takeover nest. • Results suggest that nest takeover has high adaptive fitness. • Further research on kin structure continues. Introduction  There are several reports from Europe and Japan about unrelated bumblebee queens of the same or different species forming a mixed colony, suggesting that nest takeover occurs in nature, although a foundress queen can build a colony herself. A possible cause of this phenomenon may be a limited number of suitable nest sites and variation in when queens wake after overwintering. Clarification of bumblebee life cycles is important in understanding the adaptive significance of social parasitism, but field observation is very difficult.   Therefore, we studied the impact of nest takeover on colony development by Bombus ignitus by using laboratory reared colonies.  0 200 400 600 800 Worker Male New queen Total Number of individuals non-takeover queen takeover queen Search for  nesting site Nest foundation  Death of foundress queen and colony decline Emergence of workers Hibernation of mated queen Production of reproductives  (new-queens and males) Mating New queen and male Spring Summer Autumn Winter Egg cups ( 3 – 10 eggs/cup) Results Removed foundress Added post-hibernation queen Annual life history of Bombus ignitus Impact of social parasitism on colony development of Bombus ignitus  

Impact of social parasitism on colony development of Bombus ignitus

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