WOOLLY APHIS.

Shannon News, 1 April 1924, Page 3

WOOLLY APHIS.

NATURAL PARASITE INTRODUCED. The introduction Qf aphelinus mali, Oil* the parasite of the woolly aphis into this district by Mr H. Taylor, orchardist, of Beacn road, Weraroa, is a development which will apparently reduqe the work of a iruitgiower in his perpetual battle witn uie pests of the orchard, very considerably in the near*future. The aphelinus is the natural enemy of th;e aphis, whose presence is necessary that it may complete its life circle, and which it invariably kills in the process. From the work at present hieing done hy the parasite in Mr Taylor's orchard it would appear that in less than two seasons alter introduction, furtlaer necessity lor the existence of the aphis will have ceased.

The following description from the official pamphlet of the Cawthron Institute, Nelson, from which* the parasite was obtained, will be of interest:

"This parasite is a tiny chalcid wasp, measuring about one-twenty-fifth of an. inch in length. In shape it is somewhat like a noney-bee, but thje colour is blackish, except for a yellowish hand round the base of the aJbdomen, and another on the antennae. It is an active little insect, arid can both jump and fly quickly. The males can be recognised by being slightly small and less stoutly built than, thie, females. Immediately on emerging from the chrysalis or pupa, the males and females pair. After pairing, ..the male lives' only a few. days, but the females may liv,e a week or longier. The fe•malel begins to search vigorously for woolly aphis, and proceeds to lay her eggs in them, one by one, by stabbing with her sharp ovipositor, at the same time, inserting one egg in each aphis. The aphis objects to this, squirms, and often exudes a drop of liquid-, but thei wound soon heals. In a few days time, a tiny wasp-grub hatches out of. the egg, and proceeus to devour th,ei whole of the internal organs of the aphis, which contains just enough food t.Q bring this grub to full size. When full-grown, the grub hardens the shell of the dead aphis into/ a kind of cocoon, within which it turns into a pupa or chrysalis. Dead aphids containing aphelinus pupae can always ibe recognised by their black swollen appearance. After a varying period of time, spent as a pupa, the aphelinus emerges as the perfect insect, and pairing again takes place. During warm summer weather the complete of the parasite is gone through in five or six weeks, so that from four to six broods a year can be.raised in a -fairly warm climate. As each female lays fifty or more eggs, the rate of increase is very great, and the parasite is able to catch up with the aphis and entirely overtake and destroy it before thiei end of the season., Aphelinus will attack any of the dark-coloured aphids, such as' black aphis of citrus trees and has been known to attack young mealy-bug. Experiments have shown clearly that, provided the sprays for woolly, aphis are omitted, the whole of the remainder of the usual spraying programme may be gone through without material! damage to thig parasite. Arsenical sprays and fungicides have no effect upon it, whilst contact sprays only damage it in. as far as they damage its host, the [woolly aphis. , The parasite 1 spends the winter as a chrysalis or pupa in. dead aplUs shells, 'either sticking to the twigs or else washed off into the ground. Hence, when pruning, all twigs which have dead Woolly aphis on them should be carefully.saved and kept in a dry place and can be used to hplp to start the parasite early in the spring or sent to one's friends to start the parasite* in their orchards. The parasite was introduced into his orchard by Mr Taylor eairly in last summer, when 300 were obtained from Nelson. These were colonised on two trees and have now spread right through the orchard. When a ""News" representative visited the orchard recently, the work of the little insect was very apparent. What had apparently been large colonies of woolly aphis had in v a great many instances been completely killed out and the branchjes. which were covered with the usual woody protuberances were recovering their normal shape and forming a new coating of hark.

The dead shells of the aphis wiere thick in some parts,, each hearing a small hole near the head whence the parasite had made its exit. As has been pointed out the-apheli-nus mali hibernates in the body of the aphis during the winter and Mr Taylor has generously announced his willingness to supply any oircliardlst who applies—in as far as is possible —with sufficient to start the parasite in their own orchards.