20 



BULLETIN 746, U. S. DEPARTMENT OF AGRICULTURE. 



and another egg is deposited, part of it extending over a portion 

 of the surface of the first egg. More eggs are deposited in the same 

 way, the female gradually moving downward and backward, so that 

 she stands over the slowly enlarging cluster. As the eggs overlap, 

 one being deposited partly over the other, the completed cluster 

 more than ever resembles a group of fish scales (see PL II). 



In this action the moth is very quiet, her wings folded, antennae 

 back, and legs apart. She keeps the tip of her ovipositor pressed 

 against the leaf continuously, making it difficult for an observer to 

 ascertain the exact time any one egg is deposited. During the action 

 she raises the body " on tiptoe," relaxing and resting against the 

 leaf at intervals. One cluster of 6 eggs was formed in 16J minutes, 



and another moth laid 



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Fig. 6.— Diagram showing relationship of mean tempera- 

 ture to length of egg period of the sugar-cane moth 

 borer, and indicating line of calculated means. The 

 dots represent period means of individuals. 



34 eggs in 8 minutes. 

 Oviposition is be- 

 gun at dusk and con- 

 tinues throughout the 

 night, the female fly- 

 ing and walking occa- 

 sionally. Many clus- 

 ters of different num- 

 bers of eggs may be 

 formed in the same 

 night. Individuals 

 deposit eggs during 

 one, two, three, or 

 four nights, never 

 longer. 



Oviposition 



is extended over several nights in cooler weather. Males in the same 

 cage with egg-laying females are indifferent, paying no attention to 

 their mates. 



EGG. 



DURATION OF THE EGG STAGE. 



The duration of the egg stage has been found to be from 4 to 9 

 days, depending on the temperature, with the average for the year 

 a trifle over 5 days. These results have been obtained from experi- 

 ments in the insectary, but it is probable that greater variations 

 between the minimum and the maximum periods occur in the field. 

 The period of incubation has been lengthened to 12 days by placing 

 the eggs in an ice box and it is likely that they will stand even 

 greater retardation without being killed. The temperature in the 

 ice box was not very low and eggs laid in the early spring or late 

 fall would probably require as long to hatch. The average length 



