THE PEAR THRIPS IN CALIFORNIA. 



43 



Table X. — Maximum and minimum temperatures during period of incubation for eggs 

 of the pear thrips, San Jose, Cal., 1910. 



Date. 



Maxi- 

 mum 

 temper- 

 ature. 



Mini- 

 mum 

 temper- 

 ature. 



Date. 



Maxi- 

 mum 

 temper- 

 ature. 



Mini- 

 mum 

 temper- 

 ature. 



Mar 10 



° F. 

 73 

 72 

 57 

 71 

 68 

 70 

 70 

 69 

 62 

 61 

 60 

 57 

 61 

 57 

 60 

 59 

 57 

 51 



° F. 

 44 

 48 

 48 

 44 

 49 

 44 

 53 

 54 

 50 

 48 

 51 

 47 

 46 

 39 

 37 

 44 

 44 

 42 



Mar. 28.. 



° F. 

 64 

 69 

 76 

 78 

 70 

 63 

 66 

 75 

 67 

 65 

 64 

 66 

 66 

 61 

 56 

 66 

 72 

 74 



° F. 

 40 



40 

 41 

 43 

 45 

 43 

 46 

 41 

 46 

 46 

 40 

 45 

 47 

 51 

 47 

 46 

 41 

 41 



11 



29 



12 



30 



13 



31 



14...' 



Apr.l 



2 



3 



4 



15 



16 



17 



IS 





19 



6 



20 



7 



8 



21 



22 



9 



10 



23 



24 



11 



12 



25 



26 



13 



14 



27 







NUMBER OF EGGS DEPOSITED BY A SINGLE FEMALE. 



Up to the season of 1910 only conjectures had been maae as to the 

 number of eggs a single female would deposit, but by taking indi- 

 viduals as soon as they emerged and placing them separately upon 

 twigs in the mica cages described under the heading "Length of egg 

 stage/' the total progeny of a single female was ascertained — approxi- 

 mately, therefore, the total number of eggs possible for one individual 

 to deposit. Each individual was allowed to remain undisturbed on 

 the twigs inside the cage. After the eggs hatched the larvae were 

 removed and counted, yielding the following total number: Cage 1, 

 155 larvae; cage 2, 146 larvae; cage 3, 142 larvae; cage 4, 99 larvae; 

 cage 5, 117 larvae. The maximum number of eggs laid is 155, 

 the mininium. 99, and the average 131.8. This is probably close to 

 the average number of eggs that would be deposited by a single female 

 out in the field, although some few long-lived individuals would 

 perhaps exceed 200 eggs. 



DEPTH EGGS ARE DEPOSITED IN TISSUE. 



The eggs are deposited within the plant tissue immediately under- 

 neath the outer epidermis and are inclosed by the tissue. The places 

 where they have been deposited can readily be found with the aid of 

 a hand lens because of the little swellings on the stems and by the scars 

 left where the ovipositor had been inserted into the plant. 



FIRST APPEARANCE. 



The very first larvae appear on almonds, apricots, and the early 

 plums, usually about the 1st of March. Larvae begin to hatch on 

 prunes and pears the middle of March and usually are in maximum 



