1922 



ENTOMOLOGICAL SOCIETY. 



Life History. 

 The Egg. 



Description: The egg is flattened spherical in shape, and measures .15 mm to 

 .16 mm in diameter. When newly laid, it is pearly to pink in colour, and later 

 on becomes a dull dark red. At the apex there is a hair-like . process about as 

 long as the diameter of the egg. 



The overwintering and summer eggs are similar in size, shape and colour. 



Location: The overwintering eggs are located on the bark anywhere from the 

 tips of the twigs to the trunk, usually on rough bark and in the axles of shoots 

 and spurs. 



The summer eggs, in the early part of the season, are laid on any part of 

 the upper or lower surface of the leaves and on the petioles. Later on, some of 

 them are deposited on the bud scales and on the bark. 



Hatching of Overwintering Eggs. The eggs commence to hatch at the time 

 European plums are in full bloom. In the plum orchard (situated near the 

 lake shore) which we had under observation this past season, the period of hatch- 

 ing extended from May 2nd to May 9th. 



Incubation Period of Summer Eggs: The period of incubation in our experi- 

 ments varied according to the temperature, from 13 days in the spring, to 6 

 days in midsummer. The average for the season was about 9 days. More 

 precise data on the duration of the e^g stage is given in table No. 2 : 

 TABLE No. 2 — Showing Duration of Incubation 



Brood 



No of 

 Exp's 



No of 



Eggs 



Time of year 



Incubation Period 



Temperature 





Min. 



Max. 



Aver. 



Min. 



Max. 



Mean 



2nd 



10 



72 



May 23rd. to June 10th 



10 



13 



10.5 



40 



85 



61 



3rd 



13 



81 



June 19th to July 8th 



7 



8 



7.5 



48 



97 



74 



4th 



13 



134 



July 11th to July 26th 



6 



8 



7.0 



60 



91 



77 



5th 



16 



110 



July 30th to Aug. 19th 



8 



11 



9 



52 



85 



69 



6th 



14 



89 



Aug. 24th to Sept. 12th 



8 



11 



10 



48 



92 



60 



Stage of Growth when First Summer Eggs are Laid: The first generation 

 adults commenced laying eggs about May 25th, or, in other words, ai the time 

 the calces on early varieties of plums were beginning to fall. 



Immature Forms. 



During its growth the spider mite moults three times and thus passes 

 through three immature stages. The newly hatched mite is termed the larva, 

 after the first moult it is the so-called first nymph or protonymph and after the 

 second moult the deutonymph. 



Description: The larva is oval in shape, sparsely clothed with long bristles 

 delicate, pearly pink to dull red in colour and measurss about .16 mm bv -0S3 

 mm. It has only three pairs of legs. 



The protonymph has four pairs of legs and is somewhat darker in colour 

 than the larva. It measures .198 — .270 mm. x .162 — .198 mm. 



The deutonymph in shape an'd colour resembles the other immature forms, 

 n The legs are translucent and sparsely covered with bairs. Like th" linn and 

 first nymph, the deutonymph is very delicate and soft-bodied. In size it is .32 mm. 

 — .36 mm x .23 mm. 



