Citrus Pests : (I) The Dicky Rice Weevil.

New Zealand Journal of Agriculture, Volume 56, Issue 5, 20 May 1938, Page 345

Citrus Pests : (I) The Dicky Rice Weevil.

W. Cottier,

Entomologist, Plant Diseases Division, Plant Research Bureau

THIS dicky rice weevil is a recent addition to our list of insect pests of citrus. . It was first recorded from New Zealand in the North Auckland district in March, 1935. The insect ,is a native of Australia where in addition to citrus it . has been recorded from apple, peach, and various garden plants. Appearance of Insect. The adult weevil measures approximately 21 mm. to 3 mm. in length and is brownish with greyish-white markings on the prothorax, wing covers, and legs (Fig. 1, No. 5). The front of the head is prolonged into a short snout (Fig" 1,

No. 6). Males may be distinguished from females by the presence of a long, curved spine and a smaller spine on each of the two front legs (Fig. 1, Nos. 8 and 9). According to Woodhill and Allman (1927) the eggs are dark amber in colour, ellipsoidal in shape, and 4 mm. long. The same authors state that the larvae when full grown are. whitish-coloured, legless grubs about 3 mm. long having a circle of distinct reddish-brown bristles on the upper surface of the last body segment. Pupae are of the same colour and approximate size as larvae, with legs, wing covers, eyes, . and antennae of the adult insect plainly visible.

Nature of Injury. Adult weevils eat pieces out of the tender young foliage (Fig. 2), but a more serious habit is the feeding that takes place on the surface of the fruit, the skin being chewed to form a network of irregular furrows which later discolour and cause marked disfigurement (Fig. 3). It is reported that up to 70 per cent, of the fruit may be badly disfigured and growth may be retarded or arrested by the attacks on the foliage. ■ '• .••• Life-history and Habits. The life-cycle in New Zealand is not known except that there are adult

forms present in August and also in the February-March period. In New South Wales, Australia, there are two generations per year, the beetles of the first generation emerging from the soil from August to October and the beetles of the second generation in the February-March period. It would therefore appear possible that there. are also two generations per year in New Zealand. The adult weevils lay their eggs in the soil, and, ' according to Woodhill and Allman (loc. cit.), the eggs laid .by the August-October generation hatch about twenty-eight days later. The larvae feed on the roots of citrus, especially nursery plants, but have been reported from the roots of apples, peach, and various garden plants. The winter is probably passed in the larval or pupal stage. .. ■ ■ The weevils have never been known to fly and are normally - unable to gain access to a tree unless they can crawl on to it. Experiments in Australia are stated to have shown that they are able to crawl a distance of 40 ft. from tree to tree. Control. In controlling this insect advantage is taken of the fact that the dicky rice weevil has never been known to fly, and control consists of banding the trees with a suitable tree-banding material. 'This is a thick “ tacky ” greaselike substance, usually vegetable in origin, which is applied in a band about 2 in. wide round the trunk of every tree at a point below the first branch.' Bands should be l in. to | in. in thickness. If the material is to be used where the direct rays of

the sun do not strike, it may be applied direct to the trunk. If, however, the band is to be exposed to the . sun it is advisable to tie a . piece of grease-proof paper very,, closely round the trunk and to apply the banding material to the paper. Where bands are applied direct to the trunk their positions up or down should be shifted from year to year to avoid possible bark injury. Bands should be freshened from time to. time by rubbing or by applying more material. To prevent contamination 'by dust as far as possible bands should : be placed as high up on the . trunk as will allow them to carry out their function. Before banding is done the branches of

the trees should be jarred sharply with a padded pole or other suitable means to dislodge any weevils that may be already " oh'the tree. To prevent weevils’ gaining access to the tree - through contact of twigs' with' the soil all foliage must be kept trimmed at, least a foot from the ground. All weed growth round trees must be kept well down, otherwise these are likely to bridge the gap between ground and foliage. ' . Literature cited. -1927. Woodhill, A. R.; and Allman, S. L. : “The Dick/ Rice Weevil.” Agric. Gaz., N.S.W r , 38, pt. 10, pp. 791-799- ■'<