FIGURE 12.
A—1, Codlin moth; 2, codlin larva in apple. B—1, Currant clear-wing moth; 2, clear-wing moth larva in stem. C—1, Tomato stem-borer moth; 2, larva of moth; 3, damaged tomato stem. D—1, A long-horn beetle; 2, larva of long-horn beetle. E—1, A leaf-mining fly; 2, leaf attacked by leaf-miner. F—1, Subterranean grass-caterpillar moth; 2, subterranean grass-caterpillar. G—1, A click beetle; 2, a wire-worm. H—1, Larger narcissus fly; 2, smaller narcissus fly. K—1, A subterranean spring-tail; 2, a leaf-eating spring-tail.
Round-headed Borers.—Apple, almond, and citrus trees, together with gooseberry and such ornamental and shelter trees as poplars, tree-lucerne, and goat-willow, are sometimes damaged by round-headed borers, which tunnel in the stems and branches. These borers ([Fig. 12]d) are white in colour, narrow-bodied, and cylindrical, the segments being usually well defined, and belong to a group of beetles known as long-horned beetles, a group of insects to which the common hu-hu beetle belongs. These beetles are narrow-bodied, and their antennæ are comparatively long and conspicuous.
To control these pests, the only thing to do is to cut out and burn the badly-infested parts. Where a borer is located (and this can be frequently done by the presence of the powdered wood ejected from the burrows), the culprit may be killed by injecting into the tunnel some carbon bisulphide and plugging up the openings with some clay or other similar substance.
Leaf-mining Flies.—Very often the leaves of cineraria and chrysanthemum are disfigured by the tortuous tunnellings of the maggots of minute flies ([Fig. 12]e). The adult insects are two-winged, and in structure resemble in many respects miniature houseflies. The eggs are laid in the leaf tissues, in which the whole development of the maggots and pupæ takes place. The white maggots are small, legless and headless. Spraying with black-leaf 40 would act as a deterrent to the flies, while infested leaves should be removed and destroyed before infestation becomes general.
Grass Grub (Odontria zealandica).—As explained in the preceding chapter, the grass grub is the larva of a native cockchafer beetle ([Fig. 11], 1). This grub, by feeding upon roots, causes extensive damage to pastures and lawns, as well as to many garden plants, including strawberries. In the case of pasture and lawns, the presence of even a considerable number of grass grubs is not detrimental unless they occur concentrated in definite areas, when the damage is pronounced. With garden plants, however, which are isolated when compared with the dense root masses of grasses, the attacks of one or two grubs upon the roots of a single plant may cause serious injury.
Grass grub damage to grasses is not merely due to attack upon the roots. While feeding, the grubs swallow soil with the roots, rendering the former spongy, and so disturb the normal circulation of moisture about the grass roots. In the case of infested lawns, it is advantageous to roll infested areas in order to pack the soil pulverised by the grubs, and re-establish normal circulation of soil moisture. Another important feature in grub control is to stimulate root development by means of fertilisers. A recently-developed method of “grub-proofing” lawns is to broadcast over every thousand square feet of turf to be treated one bushel of screened sand or clean soil, in which 5lb. of lead arsenate powder have been intimately mixed. This is said to remain effective for a period of three years; but such fertilisers as nitrate of soda, superphosphate, sulphate of potash, and potassium chloride should not be used on “grub-proofed” turf, as they react with the lead arsenate, and reduce its effectiveness, though rotted manure or ammonia sulphate may be used.