An Experimental Study of the Effect of Group Size on Larval Growth and Survivorship in the Imported Willow Leaf Beetle, Plagiodera versicolora (Coleoptera: Chrysomelidae)

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Abstract
The larvae of the imported willow leaf beetle, Plagiodera versicolora (Laicharting), feed in coordinated groups of full and half siblings during early development. When disturbed they exude an antipredator chemical, which may be more effective in groups. Two experimental studies were conducted to test for a group advantage. Groups of initial size 2–10 or 2–14 larvae were established and sampled from days 1 to 6 after hatching. The first study showed no effect of group size on survivorship nor on average leaf area consumed, but there was a significant effect of group size on larval growth. This suggested an increase in feeding efficiency with group size. In the second study the initial average rate of cannibalism for a group had a significant effect on subsequent individual growth rates, and survivorship increased with group size.