The Cane Grubs of Australia. 25 



THE SCOLIID PARASITES. 



The three scoliid parasites known to attack the cane-grubs are Dielis 

 fcrmosa Guerin, Discolia soror Smith, and Canipsomcris radida Fabr. ; 

 the first-named has long been known as an enemy of Lepidiota alhohirta, 

 the other two have been discovered by this laboratory. The larva attaches 

 itself to its host on the venter of the thorax or basal abdominal segments 

 where it remains until full-grown, finally spinning a cocoon and pupating 

 against the skin of its victim. Little has been learnt as to the habits 

 of the species; it would seem that Dielis forniosa is the most common 

 in canefields, and Discolia soror in sand or sandy loam ; as they probably 

 have similar habits, the data for the three are taken together. 



Experiments have been tried to effect the breeding of the parasites 

 in confinement, but without success. On June 25th a female Campsomeris 

 radula, caught on flowers, was placed in a bottle containing a Stage III. 

 larva of Aiwplognathus hoisduvali in about an inch of soil; in a few 

 minutes the wasp attacked the larva, holding it by an anterior leg, the 

 larva meanwhile making frantic efforts to seize its enemy which after a 

 short delay stung its victim on the venter of the first thoracic segment 

 and paralysed it immediately; the wasp now attempted to bury the 

 larva, catching it by the mandibles for this purpose, but the depth of 

 earth being insufficient, again seized it by an anterior leg and remained 

 for some time with the tip of its bod}^ against the venter of the thorax 

 of the larva as though ovipositing; however subsequent examination 

 revealed no trace of an egg, and if deposited it must have been inter- 

 nally ; the larva did not recover from the attack, remaining in a limp 

 paralyzed state merely feebly moving its mouth-parts until July 20tli, 

 when it commenced to turn black from the anal end and to decompose 

 a few days after. A second female of the same species was confined on 

 the same date in a similar manner with a Stage III. larva of Lepidiota 

 caudata; the actions of the wasp in attacking the larva were exactly 

 alike except that no short delay occurred after the victim was seized 

 before it was paralyzed ; the larva in this case died within a day or two. 

 On November 29th, a female Dielis formosa was captured and placed in 

 a glass jar containing two Stage III. larva' of Lepidiota caudata] both 

 were paralyzed the same day, one died on the following date, the otliin- 

 remained limp and inactive until December 20th when it commenced 

 to shrivel and was dead on the 22nd. On August 19th a Stage III. 

 Anoplognathus hoisduvali larva was ploughed up, attached to which was 

 a small Scoliid larva, which at once became detached ; the host remained 

 inactive until October 24th when it began to shivel and was dead on 

 the 27th. These records show that the larva does not recover from the 

 attack of the wasp though it may remain alive for some considerable 

 tiine; in this respect one is reminded of the paralyzing of spiders, cater- 

 pillars, &c., by the PompilidiP and Eumenida\ Tryon (Queensland 

 Agric. Journal, vol. x.. No. 2, 1902) states as regards the attack of tht> 

 larva of D. formosa, " for, notwithstanding the fact that the beetle-grub 

 continues for a while to feed, its body gradually becomes more or less 

 flaccid and collapses." From our observations above-mentioned, this 

 statement of the host grub continuing to feed would appear incorrect; 

 moreover it is natural to suppose that in moving through the earth a 

 healthy grub would soon dislodge its external parasite, and we cannot 

 see how the parasite could remain attached to its host under such 

 conditions. 



