24 BULLETIN 491, U. S. DEPARTMENT OF AGRICULTURE. 



OVIPOSITION. 



Age when oviposition begins, — The age at which oviposition begins 

 has never been determined broadly until the present investigation. 

 Information on this point is of importance, as the adult appears to be 

 the most vulnerable point in the life cycle of this pest from the stand- 

 point of artificial control. Severin, who first undertook to solve this 

 problem, states (45) that "a large number of adults upon emerging 

 were kept in breeding jars and fed on diluted molasses, fruit and vege- 

 table juices, and water. After having been kept in captivity for 8 

 days 3 females were dissected, but no fully developed eggs were found 

 in the ovaries. A daily dissection of 3 fruit flies was continued from 

 now on, and at the end of 14 davs 23 ripe eggs were counted in the 

 two ovaries of one fly, but others did not show mature eggs in the 

 ovaries at the end of 16 days. At the end of 17 da} r s 31 eggs were 

 dissected from the ovaries of another specimen. In all probability 

 the effect of confining the insects in breeding jars plays an import- 

 ant part in the rate of development of the eggs." These dissections, 

 Severin concludes, indicate that egg-laying begins 14 to 17 days 

 after the adults emerge. • 



As noted under the subject of " Mating," varying types of food 

 supplied adults in captivity may have widely varying effects upon 

 the development of the eggs. Thus, four lots of adults emerging on 

 October 24, 27, 28, and 29, 1916, comprising a total of 1,230 flies, 

 which had constant access to the juice of fresh cucumbers cut open, 

 began ovipositing in 12, 11, 11, and 11 days, respectively, each lot 

 depositing from 17 to 29 eggs the first day. The mean average tem- 

 perature during this experiment was 76.4° F. and the mean relative 

 humidity 69.1 per cent. When fed upon papaya and water a most 

 surprising difference results in the rapidity of egg development. 

 The experiment was repeated many times during the years 1913, 1914, 

 and 1915 and many hundreds of adults were used. Thus with a 

 mean temperature averaging 75.5° F. and the mean relative humidity 

 69.3 per cent females did not begin ovipositing until about one month 

 after eclosion. "While fruit was placed in jars with about 1,000 

 adults which emerged from May 23 to 25, no attempts at oviposition 

 were noted until June 23, when 12 punctures containing no eggs were 

 made in a mango by females that emerged on May 24. The first 

 eggs. 12 in number, were laid on June 25, or 32 days after eclosion. 

 No eggs were obtained from females that emerged on May 25 until 

 June 28, or 34 days after eclosion. This is remarkable when com- 

 parison is made with females that were fed on cucumbers and which 

 began ovipositing when only 11 to 12 days old. 



Adults emerging on January 3, 1916, during the coldest portion 

 of the year at Honolulu, and fed on papaya and water when the 



