19 



of moisture raised the " heat paralysis " point, and so gave opportunity for 

 more rapid development. 



It is also well known that their development is retarded by periods of wet 

 weather, such as prevailed in Central and Eastern Canada during the spring 

 and much of the summer of 1912. Such periods of excessive humidity are, 

 with us, invariably cold, so that we have both retarding influences in operation. 

 There is also the important factor of fungus development which is so much more 

 rapid in wet seasons, and both renders the bark unfit for food and at times 

 destroys all stages of the beetles in large numbers. 



We may safely conclude that warm and moderately dry seasons, with abun- 

 dant sunlight, are the most favourable for bark-beetle development; and that 

 cold and wet seasons are the most unfavourable. 



MATING HABITS. 



This subject is treated in parts of this series dealing with the biology of 

 the species, planned for later publication. With many species copulation takes 

 place during the migratory flight from the old trees to the new, either on the 

 bark of the old trees or after alighting. With Anisandrus, in which the males 

 are unable to fly, paring takes place at the mouth of the old tunnel or possibly 

 within it, but probably in most cases on the bark of the trunks containing the 

 old tunnels during the later summer. Monogamous species pair often at the 

 mouth of the new tunnel and one mating may be sufficient to fertilize the 

 greater part of one lot of eggs; polygamous species usually mate at the entrance 

 from the nuptial chamber into an egg-tunnel, and with these species mating 

 occurs frequently. 



THE OVIPOSITION. 



With many species, oviposition takes place in the manner described for 

 the following two. The oviposition of Pityogenes hopkinsi Sw. was observed. 

 The egg-niche was cut at the extreme end of the egg-tunnel, and when the tunnel 

 was examined, the female was in the tunnel end with ovipositor inserted into 

 the niche. In a few seconds the egg appeared and adhered to the bottom of 

 the niche. The time of passage was about one second. As soon as the egg was 

 deposited the female moved forward to the nuptial-chamber, reversed her 

 position, and entered the tunnel head foremost. When she reached the tunnel 

 end she appeared to move the egg with the mandibles, probably placing it more 

 evenly, and then turned her attention to filling a crack in the tunnel roof with 

 boring dust. The tunnel had been previously opened and covered with sheet 

 celluloid, so that the beetles within could be watched, and the celluloid had been 

 moved just previous to oviposition. Some of this dust she pushed in from the 

 nuptial-chamber (the male had been removed and the nuptial-chamber was 

 partly filled with boring-dust), and the rest she removed from the tunnel end. 

 This finished, she continued the excavation of the tunnel, placing the boring-dust 

 thus obtained about the egg until the niche was filled. 



The Dendroctonus simplex female cuts its short egg-groove or egg-pocket 

 at the extreme end of the tunnel as then cut. It then backs out to the nearest 

 turning-niche, or possibly ventilation-hole, reverses its position, proceeds back- 

 wards to the end of the tunnel, and inserts the tip of the abdomen into the 

 egg-pocket. In one case observed by the writer, the tunnel end was opened, 

 revealing the female in position for ovipositing. She remained in that position, 

 almost motionless, for six minutes, until, suddenly, the egg appeared, or rather, 

 as the ovipositor was placed against the bottom of the pocket, and the egg was 

 large, the beetle appeared to walk away from about the egg, leaving the latter 

 adhering to the wood. The female then moved forward to the nearest turning- 



361982^ 



