PROCEEDINGS OF THE 



ENTOMOLOGICAL SOCIETY OF WASHINGTON 



VOL. 22 NOVEMBER 1020 Xo. 8 



OBSERVATIONS UPON THE INSTARS OF PHRYGANIDIA 



CATERPILLARS. 

 By FRAXK B. HERBERT, Bureau of Entomology. 



The larva of Phryganidia californica Packard, the California 

 oak worm, which spasmodically defoliates the oaks in the coast 

 region of California, has been studied for several seasons by the 

 writer. During this study some interesting facts came to light, 

 which are not contained in the Farmer's Bulletin Xo. 107<> (The 

 California Oak Worm), but which might well be published. 



dumber af Instars. 



A great number of larvae were followed through their stages 

 under artificial conditions for several different seasons and the 

 observations checked up with those under natural conditions in 

 the field. The number of instars was found to be five in the larger 

 number of cases. However, several larvae passed through only 

 four stages while others passed through as high as nine. 



Usually there appears to be some dissension over the correct 

 number of instars for a certain caterpillar. This caterpillar is no 

 exception to the rule for in one paper written by Kellogg and 

 Jack 1 in 1895, six larval stages are described. Also in an un- 

 published paper, 1913, by R. S. Raven, 2 then a student of the 

 University of California, the number of instars was stated to be 

 four. Both parties must have observed abnormal individuals. 



The amount of food available and the temperature are im- 

 portant factors in the development and the number of molts 

 which the caterpillars undergo. Warm weather and plenty of 

 fresh food produces the smaller number of molts, while cold weather 

 and the lack of fresh food produces the larger number. One cat- 

 erpillar which normally should have pupated in the late fall was 

 carried over winter in the laboratory to the next spring, mean- 

 while passing through nine stages. 



Fifth instar caterpillars are of two different colors, the normal 

 ones turning dark while a number of them retain the predominant 

 yellow color of the earlier stages. Light seems to be a factor in 

 determining their color, plenty of sunlight producing dark in- 



1 Kellogg, V. L., and Jack, F. J. Cal. Acad. Sc. Proc. 2nd Series, Vol. 

 5. pp. 562-570. 1895. 



2 Raven, R. S. Thesis for B. S. degree. Univ of California. 1913. 



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