HORNTAIL BORER.

Press, Volume LXV, Issue 19610, 4 May 1929, Page 19

HORNTAIL BORER.

A PARASITE INTRODUCED. For some years past the horntail borer has been found in dead trees of several species of conifer in the State plantations at Hanmer and Balmoral, including P. radiata, P. laricio, P. ponderosa, P. Austriaca, P. muricata, P. Murrayana, and larch. It apparently eonflnes its attentions to dead or dying trees or trees of a more or less sickly nature and which would succumb in any case. Damage has been infinitesimal so far, practicaly confined to a fraction of 1 per cent., and it ia doubtful if the horntail will ever prove a serious menace to our exotic forests. The insect was noticed in this country over 20 years ago, and since then, the damage recorded is of little account considering the wide field it has had to operate over and the opportunity to multiply. Recently Dr. Millar, of the Cawthron Institute, has been rearing broods of the parasite, "Rhyssa persuasoria," for distribution throughout the infested areas, and, within the past two months, several consignments of this insect have been liberated in the State Forests at Hanmer and are now "getting busy." The female parasite, seeking out the egg 1 deposits of the horntail, sets its eggs in close proximity thereto and the grub, when it hatches out, immediately attaches itself to the grub of the horntail, on which it feeds, and so eventually kills. The parasite is very similar in appearance to the horntail, but about one third its size, the female being about twice the size of the male. It is hoped that this little insect will eventually jrreatly curtail the depredations of the horntail even if it does not entirely exterminate the insect. It was stated recently that it was commonly thought to attack only pinus insignis, but its cosmopolitan taste in coniferous tree species has been gener- i allv known to the State Forest Service for some years past, and is now more or less common knowledge.