Chemical agents that cause injuries to insects are chemical insecticides and toxins or poisons produced by plants and microorganisms.
When insects are poisoned by chemical insecticides certain cells often display an alteration of staining properties; some cells may separate from each other in the tissue and may break down.
Usually one of the first symptoms is the decreased general activity of the insect but with the retention of its abilities to crawl, walk, fly and keep its balance. As the effect of the poison increases, these abilities are inhibited, its facility for regaining its balance frequently being the first to leave. When the insect is placed on its back he unable to right itself may nevertheless be able to move legs, other appendages, and body fairly vigorously. Movement of the legs then slows down considerably until only slight movements can be detected. Eventually, slight movement can be elicited only by mechanical stimulation. When no response to mechanical stimulation is forthcoming, the insect may be considered dead.
The common insecticides that act on respiration are the arsenicals (sodium arsenite, Paris green, lead arsenate, etc.), rotenone, and cyanide. Insects poisoned by them show initial hyperactivity, followed by convulsive and uncoordinated movements, and ending in paralysis and death.
Some General Groupings of Insecticides:
Some side effects of insecticides:
Methyl bromide - twitching, turning, retching, vomiting, or the excretion of faeces of abnormal consistency. Mortality may be preceded by a prolonged period during which there is a continuous loss of weight, as occurs in the delayed mortalities.
Pyrethrum, rotenone - complete or partial discolouration or blackening of the appendages in certain insects.
DDT - in many cases assumes a peculiar and almost characteristic tremor not seen in other types of poisoning.
Petroleum oils - have a direct toxic effect, but the nonvolatile oils kill very slowly.
Nicotine - may bring about an initial exciting stimulation or irritation which is followed by stupefaction and immobility.