420 Journal of Agricultural Research voi. xv.no. s 



DIACHASMA TRYONI 



Diachasma iryoni Cameron was first observed in New South Wales in 

 1908 and was described in 191 1. It was introduced into Hawaii from 

 New South Wales by Silvestri in May, 1913. It soon became definitely 

 established and by 191 6 its importance as a parasite and its ready 

 adaptation to Hawaiian conditions were demonstrated clearly. During 

 191 7 it excelled the work of the other introduced parasites 



DESCRIPTION AND LIFE HISTORY 

 EGG 



The egg (fig. i, 2) is cylindrical, translucent white, with smooth, glis- 

 tening surface, drawn out at each end into a short, rounded protuberance 



and when first deposited is surrounded 

 by a thin, transparent membrane, 

 possibly the exochorion. This mem- 

 Fig. i.—Piac/iaiwo/ri/o wV Egg just kid; length brane adheres to the conformity of 

 °-4^™™- the egg but does not tightly inclose 



it. The egg is faintly concave ventrally and distinctly convex dorsally. 

 The protuberance on the cephalic end is slightly broader and shorter 

 than is that on the caudal end. At deposition the egg averages 0.45 mm. 

 in length, including the enveloping membrane, its greatest width being 

 about one-sixth of the length. When fully developed the &gg averages 

 0.65 mm. in length and is about one-fourth as broad as long. During 

 development the outer enveloping membrane is ruptured and entirely 

 separated from the egg proper. At maturity each end of the egg stands 

 out as an abrupt, broad tubercle. The embryo is then clearly revealed 

 by transmitted light. 



Although the eggs are deposited only slightly beneath the surface of 

 the larval skin, they are invisible even under strong sunlight and magni- 

 fication. The duration of the 

 egg period can be determined 

 only by dissections of host tissue 

 at frequent intervals to locate the 

 eggs and by the use of numbers 



. . , , , Fig. 2. — Diachasma tryoni: 'EzzTaaXm:t;\enzth. 0.6s rxm. 



of well-parasitized larvae known 



to have been oviposited in for a short and definite period. The Q.gg stage 

 in Honolulu (Table I) was found to last from 54 to 73 hours, the variations 

 depending upon fluctuations in temperature. As the average incubation 

 period is about 2^4 days, the exact number of hours required for the 

 development of eggs deposited in the morning is less than is that where 

 eggs are deposited in the late afternoon. Eggs deposited in the morning 

 hours occupy parts of three days and two nights before hatching, and 

 thus develop under a somewhat higher average temperature than would 

 obtain in the case of eggs deposited in the afternoon or early evening. 



