MONTHLY NOTES ON GRUBS AND OTHER CANE PESTS. 15 



"A single egg is laid on each grub, and hatches after an interval 

 -of about three days, when the tiny larva at once buries its head in the 

 .body of the paralyzed grub and proceeds to imbibe its juices. 



"So rapidly does it develop at this stage that nine days later those 

 destined to produce female wasps have become plump white maggots 

 nearly an inch in length and have ceased feeding. 



"Larvae of male wasps, although much smaller than those of the 

 ■opposite sex, take just as long to mature. The shortest periods recorded 

 by us, however, are seven days for the male, eight for the female, while 

 nine days appears to be the average time for both sexes. 



"Having withdrawn its head from the shrunken, distorted body of 

 its victim, the maggot, after resting a few hours, spins an oval, parch- 

 ment-like cocoon of tough brown silk, in which it gradually changes to 

 a pupa, and finally into the perfect wasp, which escapes by cutting out 

 a circular trapdoor at one end of the cocoon. 



"The average time passed in the pupal stage is thirty-six days for 

 the male and thirty-nine for female wasps. 



"We have found that C. radula will deposit eggs upon second-stage 

 .grubs of the grey-back beetle, but apparently will not oviposit on third- 

 stage grubs of Dasygnaihus australis or even paralyze them. 



"Data obtained at Meringa would lead us to suppose that this 

 digger-wasp plays an important part in the control of L. frenchi. 



"Individual females bred from cocoons at the Insectary laid two 

 eggs per day. A single wasp of the above species was confined with 

 six large grubs of frenchi in a cage containing seventy-two cubic inches 

 ^of soil, and when examined twenty-four hours later two grubs had eggs 

 on them, two were paralyzed, and the remainder killed. 



"On the preceding day, however, the same wasp paralyzed twelve 

 ^.grubs, laying an egg upon one ; she left only three uninjured of the 

 original fifteen placed into the cage. 



"Upon several occasions during early morning after rain we have 

 -observed great numbers of male wasps of C. radula and D. formosus 

 flying energetically over the surface of land supporting young cane 

 plants injured in places by larvae of frenchi. Few or no females were 

 noticed on the wing at such times, but upon digging beneath affected 

 stools several were unearthed together with grubs they had paralyzed. 



"We may therefore conclude that, although not much in evidence 

 above ground, the females, nevertheless, are usually well represented 

 in the field. 



"Such conclusion is amplj^ borne out by our laboratory tests, since 

 -out of eighteen wasps of this species obtained from eggs laid by a female 

 caught at Meringa on 26th September, 1917, nine proved to be males 

 and the same number females, and all of these parasites emerged prac- 

 tically together. 



