440 Journal of Agricultural Research voi. xv, No. s 



OPIUS HUMILIS 



The parasite Opius humilis was brought to Honoltiki from West Africa 

 by Silvestri in May, 191 3. It was soon established in the Kona coffee 

 district of the Island of Hawaii, owing to the liberation there of a few 

 individuals in June, 191 3. By October of the following year it was 



found frequently parasitizing from 

 80 to 95 per cent of the larvae devel- 

 oping in coffee in this district. Its 

 general distribution and value were 

 Fig. 2o.-opius humilis:: Egg freshly laid, proven in Houolulu Several months 



Length 0.48 mm. . , , . , 



previously. As shown by data pub- 

 lished elsewhere by the writers, the importance and effectiveness of this 

 parasite soon became greatly curtailed through the restraint operated 

 over it by the other introduced parasites. 



DESCRIPTION AND LIFE HISTORY 

 EGG 



When first deposited (fig. 20), the egg is cylindrical, transparent, with 

 smooth glistening surface, slightly curved and bluntly pointed at each 

 end. The cepahalic end is less pointed than is the opposite end. It is 

 0.48 mm. long and is neaily one-fifth as wide as long. No tubercular 

 protuberances are present at either end when first laid nor is the outer 

 enveloping membrane present that surrounds the egg of Diachasma 

 tryoni. When fully developed it is 0.85 mm. long and less than one- 

 third as broad as long (fig. 21), and is hardly recognizable as the egg 

 deposited two days previously. Each end is prolonged into a distinct 

 tubercle, the caudal end being prolonged much more than the opposite 

 end. As in D. tryoni, the egg is placed just beneath the surface of the 

 larval skin but so far as to be invisible from the surface. The wound made 

 on the larva by the oviposi- 

 tor remains permanently as 

 an oval, brown scar. 



The duration of the egg 

 stage ranges from about 45 

 hours in the summer months 

 to S"^ hours in the winter ^ ,.^. , ... ,, ^ t n, a ^.^ 



^^ Fig. 21. — Opiiis humtlis: ^laXxxre egg. Length 0.85 mm. 



months. (For temperatures 



see Table III.) This is an average of about nine hours shorter than the 

 similar period for Diac/iai-ma /ryow. Ten eggs deposited on March 24, 

 i9i7,at 10 a. m. hatched 48 hours later. One hundred and sixty-two eggs 

 deposited on July 6, 1917, between 12 m. and 2 p. m. hatched from 45 to 47 

 hours later. Forty- two eggs deposited on May 13, 191 6, between 10 a. m. 

 and 12 m. hatched 48 hours later. The differences in duration are due to va- 

 riations in temperature. The hatching of the egg and the effect of the egg 

 upon the development of the host are identical with that of D. tryoni. 



