1 Fes., 1902.] QUEENSLAND AGRICULTURAL JOURNAL. 139 
beetle grubs are nearly full fed; this is in August, in the Cairns district, and in 
September in that of the Isis Scrub. It is accordingly in keeping with this 
circumstance that it occurs in preponderating numbers then. By the time, 
however, that its immediate progeny appears, the scarabwid larve have become 
either pupe or perfect beetles, and the grubs that are necessary to receive the 
eggs of ovipositing females are comparatively scarce. Accordingly this brood 
consists to a very large extent exclusively of males; and such few female 
examples of the perfect Dzelis that do emerge put in a belated appearance. — 
The few insects resulting from the latter in February and March possibly 
pass, in most cases, the winter months in the imago condition; although 
unhatched chrysales of the insect are commonly found in the soil during this 
month. How long the insect remains beneath the earth has not been 
ascertained, but it would appear that its existence as a pupa may be consider- 
ably protracted when cold weather supervenes.* 
This hymenopterous scarabeid grub parasite is in some instances quite 
revalent. In the case of a single exploration made in the farm of Mr. R. 
Blackwell, Mulgrave River, Cairns, on the 4th August, it was observed that no 
less than 25 per cent. of the large cane-destroying grubs of the large cane- 
destroying scarabeid beetle—Lepidiota albohirta—were yictimised. In the 
Childers district (South Isis) a smaller proportion—viz., 10 per cent.—of the grubs. 
of the most prevalent cane grub of that locality, a species of Rhopea, was found 
to be similarly victimised in the course of investigations conducted by the writer 
during December, 1901. In neither locality, however, has the laborious work 
of exploring the soil to a depth of 2 feet 6 inches, or even beyond this, as is: 
necessary in such an inquiry, been prosecuted to an extent adequate to bring to: 
light the fullest degree to which the species of parasitism under notice may 
sometimes attain. 
The method of dealing with the sugar-cane “evil” to which reference is 
made, consisting as it does principally in the capture of the mature form or 
beetle as originally advocated by the writer, is not attended with the undesirable 
result of destroying simultaneously this useful insect, as oftentimes happens 
when plant depredators subject to being victimised by parasites are secured with 
a view to their subsequent destruction. The cane grubs, however, being reduced 
in numbers by this means; the destructive parasitism due to the Dielis may be 
exerted to a larger proportionate extent than, failing the prosecution of this 
method of repression, would be experienced. 
© The parasite, as may be inferred from a foregoing statement, does not restrict 
its attention to the larva of a single scarabwid beetle. In the Cairns district it 
has been found commonly attacking the grub of Lepiéota, and in the Isis Scrub 
district that of Rhopwa. There are grounds also for concluding that it also 
-victimises the larvee of Anoplognathus and Dasygnathus ; both genera that also 
include species of so-called sugar-cane beetles. ~ 
A single dead cocoon has been found in the soil already riddled with 
perforations. Whether these arose previous to death or not cannot be 
pronounced. It may be, however, that we have evidence here of the existence 
of some hyper-parasite that attends the primary one—the Déelis—as this 
pursues its quest in the soil, and that in turn lays its eges adjacent to that of the 
parasite, that its young may feed upon this grub-destroyer. 
This useful insect is not likely to lend itself to artificial propagation to an 
extent to admit of its numbers being augmented, with the result of greater benefit 
being derived from its presence in Queensland than would otherwise be ex- 
perienced. Impregnated females might, however, be transported to foreign 
* J. Sichel, writing concerning the Abyssinian insect Discolia castanea, Percheron, of which 
he had received a collection comprising forty-one males and not a single female, inakes some: 
interesting remarks on the relative frequency of occurrence of the two sexes amongst Hymenop- 
tera, and states amongst other facts in this connection that in the case of some species the males. 
appear several days, or even several weeks, before the females emerge from the soil. He does 
not, however, include, in his explanation of the exclusive appearance at:a time of individuals 
representing one sex only, a seasonal preponderance of this sex as constituting the brood of which 
it forms part. (Of. Catalogue. Appendix I., p. 279.) 
10 
