Trombidiformes 217 



is slightly longer than either larval or protonymphal stages. The fe- 

 males become larger and more globose than the males during the 

 deutonymphal stage and can thus be distinguished. The males com- 

 plete each stage in a fraction of a day less than the females, the total 

 in the Northwest for the immature stages averaging eight days for the 

 males and nine days for the females. When the male emerges it runs 

 about the leaf until it finds a quiescent female deutonymph. It then 

 settles down beside the deutonymph to await emergence of the female. 

 As soon as the nymphal skin of the latter splits across the back the 

 male begins working at the posterior half of it with his fore legs and 

 mouth parts. The female arches her back and within a few minutes 

 her posterior legs are freed. She then backs out of the anterior half of 

 the old skin and copulation takes place immediately, sometimes even 

 occurring before the female has had time to free herself entirely from 

 the nymphal skin. The male crawls under the female from the rear, 

 the latter elevating the tip of her abdomen. The male clasps his front 

 legs about her abdomen and his second pair of legs about her hind 

 legs, and then curves the end of his abdomen upward and forward 

 until it meets the end of the female's abdomen. Copulation lasts from 

 ten to fifteen minutes. Eggs are laid within a day or two after emer- 

 gence in hot weather, while in cool weather oviposition may begin 

 several days or a week later. Eggs are laid on both surfaces of the leaf, 

 usually along the midribs and veins and near the edges of the leaves.. 

 These summer eggs hatch on an average in about eight to ten days. 

 The number of generations per year depends on chmate and season. 

 Four generations are reported in Sweden, probably six in Connecticut, 

 and from six to eight in the Northwest. Overwintering eggs are de- 

 posited over a rather long period, beginning about the middle of Au- 

 gust, until the cold weather kills the mites or causes the leaves to drop, 

 sometimes as late as November. Individual females of the sixth, sev- 

 enth, and eighth broods may deposit these eggs. 



The life cycle of Metatetranychus citri (McGregor) is very similar 

 to that of M. ulmi, except that in California the adults overwinter 

 on the host and there may be from twelve to fifteen generations a 

 year. 



Tetranychus bimaculatus Harvey overwinters chiefly as mature fe- 

 males. During mild weather in the southern United States eggs are laid 

 and considerable development may take place. This species overwin- 

 ters on wild plants and in the spring, when the mites develop rapidly 

 and the food plants become too crowded to support them properly. 



