VARIATION AND HEREDITY OF BODY-LENGTH. 



13 



VARIATION AND HEREDITY OF BODY-LENGTH. 



The variation in size in some of the species is really extraordinary. It 

 is relatively slight in Epilachna, Adalia, Harmonia, Anatis, Cycloneda, 

 Paranaemia, Megilla, and Anisosticta. But in Hippodamia and Coccinella 

 H. convergent and C. novemnotata stand out as greatly more variable than 

 their co-species (fig. 2) . It is easy to see why Epilachna should not be so 

 highly variable, since the food-supply rarely becomes short for the indi- 

 vidual larva. The aphid supply is, on the other hand, very uncertain, and it 

 is a great advantage for a species to undergo metamorphosis when the food 

 falls short, even though undersized. But why are not all the aphidivorous 

 species highly variable, then? Again we may say that Adalia is more 

 constant because of its short larval period, which makes it less likely to 

 suffer from limitation of the food-supply ; but why, then, is the large Anatis 



/TK 



56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 

 01101 1 2 3 4 11 4 11 IT 11 14 15 9 16 13 9 8 1 2 000 

 00000 00 1205 1 3 6 8 6 10 16 11 9 14 9 13 16 14 12 



83 84 85 

 000 

 9 35 



86 87 



0=154 



2 0=175 



151 males ; 173 females. 



FIG. -2. Variation of length of elytra 



'i <><invcrgens, Fail-field, Washington, 1905. 



relatively constant? To determine if shortage of food-supply really could 

 reduce the size, I experimented upon Epilachna,, which one would expect 

 would be most resistant to such treatment. I was able to get healthy 

 beetles of only 5.7 mm. in length of elytra, while 8.2 mm. is not rare in 

 nature. I believe, then, that the greater part of the variation in size is 

 modificational. In addition to the factors mentioned above, it seems 

 possible that H. convergens and C. novemnotata resort to a greater variety 

 of aphids, the season of some of which is of short duration. 



