Relation between First and Second Brood Production in the Bark Beetle Ips Typographus (Scolytidae)

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Abstract
Parent bark beetles, Ips typographus, were collected when they reemerged from their first brood bolts in the laboratory. The first brood was produced at two densities, 2 or 8 females per 100 m2. Reemerging parent beetles were transferred to smaller slabs for second brood production. Each slab was infested by either a single female or a single pair. In the first experiment, the second brood emergence was recorded, and in the second oviposition was measured. On the average 42 eggs and 23 adult offspring were produced with minor differences between treatments. These results suggest that a single female is equally good at producing a second brood as a pair, and that the female density during the first oviposition period does not influence the size of the second brood. Similarly, female residence time with the first brood, body size, weight and lipid content explained little of the large variation in second brood size. In a third experiment, the egg laying of individual females was followed in both broods by using only one pair of beetles for each first brood slab. This comparison between the size of the two broods for individual females confirmed the results of the other experiments. Thus, all experiments revealed that early reemerging beetles do not compensate for a small first brood with a larger second one. The results are discussed in relation to earlier proposed hypotheses formulated to explain bark beetle reemergence.