ANNUAL REPORT, 1941 63- 



Average Number of Days at — 



60° F. 70° F. 80° F. 



From oviposition to hatching 14.48 7.71 3.81 



From hatching to adult — male 15.70 9.46 5.35 



female 19.17 11.00 6.25 



From oviposition to adult — male 30 . 94 1 6 . 95 9 . 23 



female 31.41 18.62 10. CO 



Oviposition records showed that although the female spiders laid about a& 

 many eggs at 60° F. as they laid at 70° and 80° F. in this experiment, they re- 

 quired about ten times as long to lay them. 



Studies of red spider development on various host plants continue to indicate 

 that there is some plant character which determines the rate of spider develop- 

 ment, and studies to determine this are planned. 



Spraying experiments with eleven advertised insecticides recommended for 

 combating the red spider mites on roses were applied at weekly intervals in three 

 series, using a greenhouse power sprayer at 275 pounds pressure. Of these, one 

 material was very effective and outstanding; two were moderately effective 

 and satisfactory; and eight were unsatisfactory. (See page 55.) 



The most effective material is described as Technical Mannitan Monolaurate 

 to which 1 percent rotenone and 1.8 and 2.6 percent other derris extractives have 

 been added. When diluted to 1-400 this was the only spray material which 

 reduced a natural infestation of 25 to 50 spiders per leaf to less than 5 live spiders 

 per leaf, and consistently killed 90 percent or more of the spiders without injury 

 to the plants. When diluted 1-600 this material was less effective but gave sat- 

 isfactory control. 



The other satisfactory materials, which combined rotenone and emulsified 

 dispersing oils, reduced the infestation 60 to 80 percent and permitted 10-18 

 live spiders per leaf after treatment. 



Unsatisfactory materials included rotenone combined with chlorinated hetero- 

 cyclic hex>'lamine, powdered derris root and sulfonated castor oil, a commercial 

 flour paste, monochlor naphthalene soap emulsion, a commercial preparation 

 containing castor bean extract (ricin), and rotenone combined with hydrous 

 aluminum oxide. Several of the rotenone sprays which gave unsatisfactory 

 control of the red spider mite on roses gave excellent control of the same pest 

 on potted carnations. 



Three applications in March of a dinitro dust containing 1 percent dinitro- 

 ortho-cyclo-hexylphenol killed 90 percent of the red spider mites and reduced an. 

 infestation from 25 to 2.4 live mites per leaf without injury to the foliage. 



Biology and Control of the Apple Leaf Curling Midge. (W. D. Whitcomb, 

 Waltham.) Although a strong northeast storm occurred on June 5 while the 

 midge flies were still plentiful and might have been blown a considerable distance 

 to the southwest, no new infestations outside of the previously known infested 

 area were discovered or reported. However, this midge was found within the 

 infested area in several orchards where it was not known to be present before 1941. 



In the insectary the transformation to flies was 22.54 percent from maggots 

 collected in June 1941, 45.41 percent from maggots collected in July and 11.11 

 percent from maggots collected in August. 



In the observation orchard at Westford the infestation was very heavy during 

 May and June but, because of the drought and absence of late summer growth 

 even on watersprouts, it was below normal in late July and August. Records 

 of 2117 bud tips on Baldwin trees examined at regular 3 and 4 day intervals 

 between May 9 and September 12 showed that eggs were laid on 1712 or 80.87 

 percent of them. Oviposition was concentrated in three distinct periods when. 



