14 MASS. EXPERIMENT STATION BULLETIN 352 



Proportion of Sexes 



Records of 259 flies of the overwintering generation in 1929 showed 57.5 percent 

 of them to be females and 42.5 percent males; and in four different emergence 

 cages the proportion or the female flies was slightly greater. Male flies are more 

 abundant early in the season, and in the first 5 days of the emergence period in 

 1929, 75.86 percent of the flies were males. 



Length of Life of Flies 



Under insectary conditions, either in battery jar cages or under lantern globes 

 over potted carrots, flies were very short-lived. In 1928, 1 fly lived 11 days and 

 the average life for 20 flies was 4.3 days. Female flies lived a fraction of a day 

 longer than male flies. Under experimental conditions the life of the flies was 

 considerably longer at cooler temperatures, and they lived from 7.3 to 6.6 days 

 longer at 55° F. than at 85° F., as shown in Table 11. 



Table 11. Length of life of c.\rrot rust flies at constant temperatures 

 First Generation. VValtham, Mass. 



FIRST GENERATION 



Ovjposition 



The eggs of the carrot rust fly are laid singly although as many as 10 have been 

 found together in a group. They are placed in crevices in the soil and among 

 the pellets of earth, or occasionally on the crown of the carrot if it extends above 

 the surface of the ground. When first laid, the eggs are usually partially exposed; 

 but in a short time the movement of the soil particles b\- wind or cultivation, 

 and the washing by rain or irrigation, may cover them slightly. Newly laid eggs 

 have never been found more than 2 inches away from the carrots, and cultivation 

 close to the plants or the disturbance of the soil during thinning or weeding 

 provides favorable conditions for oviposition. 



In the insectary studies, female flies have laid 35 eggs during their short life, 

 but this number is considerably above the average, which was 6 eggs in 1928 

 and 18 eggs per female in 1929. 



Under normal conditions eggs are laid one or two days after the flies emerge, 

 and oviposition continues during the life of the flies, with the greatest number of 

 eggs being laid on the third da\' after emergence. In normal seasons the egg- 

 laying period begins the last of May and extends for about a month. Seasonal 

 conditions cause some variation in this activity, as shown in Table 12. 



