Weevils appearance

When heavy infestations of weevil are controlled with insecticides rather than by drainage, the depressing effects on yield of drainage and of root destruction by weevils would be avoided. While it remains to be proved, it would appear that under conditions of heavy infestations insecticidal control without drainage should materially increase yields. Should future work show that similar results may be regularly obtained, we may conclude that insecticidal control of the rice water weevil is more effective, is cheaper, produces higher yields, requires less water, and will materially lessen the mosquito populations of the rice area. 

For the Mexican boll weevil a specially prepared calcium arsenate containing up to 20 per cent, of arsenic pentoxide is effective. This is prepared by heating together white arsenic and precipitated chalk in the presence of excess air at 650° C. The cotton plant is not injured by this preparation.10 In Peru about 30,000 acres of cotton fields are dusted annually from aeroplanes with calcium arsenate. Acid arsenates of calcium appear to be more toxic to boll weevils and to locusts than the basic arsenates. This is probably because the latter must be partially hydrolysed to compounds giving more soluble arsenic before toxic results are produced.11 The extensive application of such sprays to cotton plants is frequently followed by heavy infestations of the cotton aphis. This appears to be due in the first place to the positive photo-tropism of the winged females to white substances such as the arsenate, chalk or flour. Increase of the aphis population is then aided by the destruction by the spray of the hymenopterous parasites of the aphis.12... 

C]MVA, or [t/-l4C]glucose62 although the net incorporation was only ca. 0.02%. Although the weevil is an obligate feeder on cotton, it would appear that it can carry out de novo synthesis of the components of its pheromone. 

APPEARANCE. Weevils that are 3-6 mm in size, of various colours (the brown leaf weevil is brown with a black head and neck-shield, the beech leaf-mining weevil is black or dark brown, and the green weevil is green). 

APPEARANCE. Beetle 4.5-6 mm long, brownish with a light cross-band . Larva 5-7 mm long, creamy white with dark-brown head, more pronounced C shape than the larva of the apple blossom weevil. 

The major constraints to kava production in the South Pacific are due to various diseases and pests. Of these, a dieback disease is the most serious (Davis etal., 1996). Other diseases appear to have a lesser impact on plant productivity. Some insects and other pests have been shown to attack, though the kava weevil borer is the only insect recorded as causing serious damage. 

However, loss reduction is not the sole aim of plant protection. Certain rust and smut fungi not only damage crops, but also produce metabolites toxic to human beings and domestic animals. The chitin shield of the grain weevil contains carcinogenic compounds, quinones, which may appear in the flour prepared from the infested cereal. 

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