Leaders ofPicea sitchensis(Bong.)Carrière freshly attacked byPissodes strobi(Peck) were covered with sleeve cages to excludeLonchaea corticisTaylor. Unsuccessful empty pupal cells ofP. strobiformed during the summer were associated with leaders without cages whereL. corticislarvae were present. Unsuccessful empty pupal cells were generated during the winter in the presence ofL. corticis. Examination of all leaders in a plantation attacked byP. strobiin each of 2 yr showed predation byL. corticisonP. strobibrood that had formed pupal cells but little if any predation ofP. strobieggs or mining larvae. When the mean percentage of successfulP. strobiemergence from pupal cells was 7%, noP. strobiemerged from leaders with more than twoL. corticisper pupal cell formed byP. strobi; the following year mean emergence was 25% and the threshold for no emergence was near fourL. corticisper pupal cell. With meanL. corticisnumbers near one per pupal cell formed byP. strobi, the success of matureP. strobibrood may have been largely regulated by weather and resultantL. corticispredation.