THE MONTHLY BULLETIN". 357 



produce males, while all fertilized embrj^os appear to develop into 

 females. 



The eggs are laid on the surface of the plant, especially along the 

 midribs of the leaves, on both surfaces. The young mites feed con- 

 stantly, except whein moulting, and the process of feeding consists in 

 sucking the juice from the outer layer of cells on the leaves and fruit. 

 But little mechanical injury is done, and badly discolored leaves may 

 recover if the mites are removed. Continued infestation results in a 

 much faded and browned foliage, and even partial defoliation. The 

 truit also loses color as if put through a process of bleaching. 



The almond red spider behaves in much the same way, differing most 

 in production of winter eggs, which may remain on the trees from mid- 

 summer to the following spring before hatching. Frequently these 

 eggs are so numerous as to produce red patches on the twigs and 

 branches where they have been laid. This mite may produce more 

 rapid and serious injury than the citrus species, and is often responsible 

 for crop failures. The almond mite feeds quite generally on deciduous 

 trees, but develops most readily on almonds. It is apparently confined 

 to such fruit trees and can not be bred on clovers, as its scientific name 

 implies. It is a difficult species to rear under artificial conditions, so 

 its habits are less well known than those of the other species treated in 

 the paper. 



The yellow mite (Tetranychus himaculatus Harvey), is more nearly 

 related to the orange red spider. Its life history is much the same, and 

 has been well worked out, with the exception of the method of wintering 

 over. Our present state of knowledge indicates that this is accom- 

 plished through hibernating of very slightly active females. This mite 

 feeds on many kinds of plants, including annual crops, and in fact does 

 its greatest damage to some, such as hops. It also attacks strawberries, 

 and is found on numerous weeds. Fruit trees are not exempt, and 

 when attacked are greatly injured. The most evident distinguishing 

 character of a yellow mite infestation is the presence of considerable 

 very fine cob web, covering the foliage. 



Methods of Control. 



]\[any interesting things could be said about the habits and life history 

 of these mites, but the purpose of this paper is the discussion of control 

 methods. The first investigation of a red spider problem in this State 

 was that conducted by the State University in southern California in 

 .1902, and dealing with the orange species. This investigation devel- 

 oped the fact that the citrus red spider was very sensitive to sulphur, 

 and might be readily controlled. 



If sulphur particles were well distributed over the foliage, and 

 retained in place by any suitable means, a long continued action 

 resulted, which killed, not only those mites present at the time of spray- 

 ing, but also any hatching from eggs. This was an important advantage 

 ever the then existing treatment, which consisted in spraying with a 

 dilute solution of sodium sulfide. This treatment sufficed to kill onlv 



