Mountain pine beetles,Dendroctonus ponderosae Hopkins, and California five-spined ips,Ips paraconfusus Lanier, were reared axenically from surface-sterilized eggs on aseptic pine phloem. After 24 hr in host logs, axenip femaleD. ponderosae and maleI. paraconfusus produced the aggregation pheromones,trans-verbenol (D. ponderosae), and ipsenol and ipsdienol (I. paraconfusus). Emergent, axenically reared maleD. ponderosae contained normal amounts of the pheromoneexo-brevicomin. Axenic femaleD. ponderosae treated with juvenile hormone or exposed to vapors of α-pinene, produced the pheromonetrans-verbenol. By 25-35 days after eclosion, axenic females exposed to α-pinene vapors produced over six times as muchtrans-verbenol as wild females, suggesting that while microorganisms in wild females may producetrans-verbenol, they may also inhibit production of the pheromone or use it as a substrate.
Improvements in the rearing methods for axenic mountain pine beetles were made by standardizing the nutritional and physical composition of a yeast-fortified ground phloem diet. By eliminating handling and possible malnutrition of neonate larvae, and by use of individual rearing units to reduce hazards associated with microbial contamination, one person produced batches of 400–500 axenic beetles. Beetles produced by this method were morphologically and anatomically equivalent to and more fecund than field beetles, were significantly smaller than their parental stocks, and perhaps required more degree hours above 40 °C in developing from egg to adult.
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