These pests are between 2.5 and 5 millimeters long when adult, light to dark brown in color and have a characteristics “snout” which is prominent between the two tennae or feelers.
Sitophilus oryzae, the smallest of the two is found more often on small than large grains and has a higher temperature tolerance than S. zeamais; both species fly and thus attack cereals in the field before harvest, but flight activity is more pronounced in S. zeamais.
The eggs are laid inside the grains by the female (capable of laying 300 to 400 eggs) which chews a minute hole in which to lay each egg; this is followed by sealing the egg in the hole with a secretion.
It is therefore extremely difficult to detect by the human eye, although these “egg plugs” can be made evident by using staining techniques.
The larva (which is legless and has characteristics curved appearance) hatches and remains inside the grain where it feeds and is responsible for most of the damage; it develops into nonfeeding pupal stage and then to the adult which bite its way out of the grain, leaving behind an emergence hole and a grain which has had about half its content eaten and the remaining half reduced in quality.
Both adults and larvae feed on stored produce and are primary pests of sound, dry cereal grains. The larvae stage in the life cycle is about five weeks at 30 degree C and 70 percent RH. Adults live for about five months.
Sitophilus oryzae L and Sitophilus zeamais Motsch
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