MONTHLY NOTES ON GRUBS AND OTHER CANE PESTS. 17 



Insect Enemies of Cane Grubs. 

 "With further reference to the question of digger-wasp parasites — 

 alluded to last month — it will be of interest to mention a few facts 

 respecting the economy of Dielis formosus, which, although a well-known 

 species, has not hitherto been bred artificially from the egg, or, indeed, 

 closely studied during the earlier stages oi its life. 



"The female of this handsome digger-wasp, which measures about 

 an inch in length, is mostly black, but ornamented on the abdomen or 

 hind body with three conspicuous broad bands of bright orange colour, 



"A specimen captured in a canefield last December lived fifty days 

 in confinement at our Insectary, during which period it deposited no 

 less than sixty-five eggs on grubs of the cane-beetle, Lepidiota frenchi. 

 It may, however, have laid a number of eggs before being caught by us. 



"Its mode of ovipositing is similar to that adopted by the digger- 

 wasp, Campsomeyis radula. The white, slightly curved egg is about an 

 eighth of an inch in length, elongate-cylindrical, one of its rounded 

 ends being glued to the under surface of the third abdominal segment of 

 the grub near the legs, in such manner as to project at right angles from 

 the body. 



"After an interval of three days the young maggot ruptures the 

 free or head end of the egg, and, remaining inside the attached shell or 

 chorion, bends downwards until able to reach the skin of the paralyzed 

 host, through which the head is then inserted preparatory to sucking 

 its internal juices. 



"The average period occupied by the larval stage of D. formosus 

 during midsummer is less than eiglit days (7-75) ; and about five weeks 

 are passed in the cocoon before the wasp emerges. 



"The percentage of male and female specimens derived from the 

 sixty-five eggs already mentioned ^^'as about equal ; and although maggots 

 producing the latter sex are much the larger, they develop more rapidly, 

 and therefore mature as quickly as those of the male wasps. 



"About 8 per cent, of grubs used in this experiment died 

 prematurely, owing possibl.y to having been stung too severely, or 

 perhaps sustained minor injuries vv^hen collected in the field. In such 

 cases the parasites, of course, were unable to mature. 



' ' Fully 20 per cent, of the eggs were destroyed by a species of mite, 

 that very often occurs as a predaceous enemy on the bodies of soil- 

 frequenting white grubs. In a few cases we found that an obscure 

 disease (not yet determined) had destroyed the egg; while in some 

 instances it had been rubbed off by the legs of the insufficiently paralyzed , 

 grub. 



"In view of the fact that the entire life-cycle of this digger-wasp 

 is completed in less than two months, and that within a week after 



B 



