THE PEAR LEAF-WORM. 



11 



Another lot, deposited from April 8 to 11, began hatching April 18. 

 The incubation period was thus 8 to perhaps 12 or 13 days. The 

 twig above cited was badly wilted by the 24th, after only 50 per cent 

 of the eggs had hatched, and none hatched after this date. It is 

 probable that under normal conditions hatching would have been 

 more regular, and also that the average incubation period would have 

 been lengthened. It was observed that unfertihzed eggs hatched as 

 readily as fertilized ones. The life-history phase of parthenogenesis 

 is considered farther on m this chapter in the discussion of the adult. 



THE LARVA. 



In the field at Walnut Creek, in 1913, the first larva was observed 

 on April 1. It was about 3 days old. Two days later about 1 per 

 cent of the eggs ah'eady laid had hatched. At Red Bluff, Tehama 

 County, Cal., in 1911, most of the larvae were haK grown on April 9, 

 and in 1912 fuU-gTOwn larvas were found at Red Bluff April 22, and 

 on May 12 no more larvse could be found.^ At Suisun and Courtland, 

 Cal., in 1912, the first larvse went to the ground about April 10, but 

 at San Jose not before May 1. In 1913, at Walnut Creek, the first 

 larvae went to the ground about April 20, and after May 10 very few 

 larvae remained on the trees. It appears that in the interior valleys, 

 where the pear trees move earher, the sawflies emerge and the larvae 

 mature earher than in the coastal districts. This is doubtless due to 

 climatological mfluences. 



The first molt is cast from 3 to 8 days after hatching, the second 

 molt from 2 to 7 days after the first, the third molt from 2 to 7 days 

 after the second, and from 4 to 10 days elapse between the date of 

 the third molt and maturity of the larva, the variations being chiefly 

 due to temperature influences. The pupal molt does not take place 

 untn the following sprmg or shortly before the issuance of the adult. 

 Table IV indicates the larval life observed at San Jose, Cal., in 1912. 



Table IV. — Larval stages of the fear leaf-worm, San Jose, Cal., 1912. 



No. 



Date egg 

 hatched. 



Date lar- 

 va spun 

 cocoon. 



Active 

 larval 

 life. 



No. 



Date egg 

 hatched. 



Date lar- 

 va spun 

 cocoon. 



Active 

 larval 

 life. 



1 

 2 

 3 

 4 

 5 

 fi 

 7 

 8 

 9 



Apr, 7 



...do 



...do 



Apr. 8 



...do 



Apr. 9 

 Apr. 10 

 Apr. 12 



...do 



May 9 

 May 10 

 May 12 

 May 11 



...do 



May 

 May 17 

 May 10 

 May 11 



Days. 



32 : 



33 1 



35 j 

 33 ! 

 33 



30 ; 



37 

 28 



io 



11 

 12 

 13 

 14 

 15 

 10 

 17 



Apr. 12 

 Apr. 13 



...do 



...do 



...do 



...do 



Apr. 17 

 May 2 



May If) 

 May 12 

 May 14 



...do 



May 10 

 May 18 

 May i:j 

 May :U 



Days. 

 33 

 29 

 31 

 31 

 33 

 35 

 2G 

 2i) 



• Letter from Mr. C. B. Weelts, Tehama c;ouiity horticultural commissioner. 



