Fumigant action

Accessibility of the deposit to the insects by contact is the chief feature of the small vial method, but fumigant action cannot be eliminated entirely. In the case of DDT this has been found to be unimportant, for flies kept in the vials out of contact with the surface are not affected. But with 7-hexachlorocyclohexane or parathion there is a noticeable toxic effect. If the vials are stood upright, laid on the side, or hung upside down, there is a decrease in the mortality produced in the order given. The position on the side has been adopted because it avoids extremes and because practical use of an insecticide often involves limited but not accentuated ventilation. 

It has already been pointed out that fumigant action requires favourable air/water partition and weak adsorption ethylene dibromide owes its success to these properties which... 

DDVP(Dlehlorvos, Vapona)/ Insecticide with fumigant action... 

Toxicity Pirimicarb has an acute oral LD50 of 147 mg/kg in rats, 107 mg/kg in mice, and 100 to 200 mg/kg in dogs. The acute dermal LD50 for rats and rabbits is more than 500 mg/kg. The acute LC50 (6 hours) for rats is 0.3 mg/L. Pirimicarb is a mild irritant to eyes of rabbits. In view of its high toxicity and fumigant action, this insecticide should be handled with care by trained and qualified workers under proper supervision. 

Pathak, N., Yadav, T.D., Jha, A.N. and Vasudevan, P. (1997) Contact and fumigant action of volatile essential oil of Murraya koenigii against Callosobruchus chinensis. Indian Journal of Nematology 59, 198-202. 

Gallery, D.J., The effect of gas velocity on fumigant action of nicotine, dichlorvos and hydrogen cyanide, ]. Stored Prod. Res., 3,17,1967. 

Parathion is an effective insecticide for a range of insect pests. It has nonsystemic, contact, stomach, and fumigant actions. Because of its high acute toxicity, parathion is no longer approved for use on fruit or vegetable crops and is severely restricted in grain crop and other uses. Parathion has no approved residential use. 

Parathion-methyl, like parathion, is a rapidly acting contact and stomach poison. It also has some fumigant action. Its range of action is similar to that of parathion. In insects it is metabolised to the respective 0x0 analogue. 

Dichlorvos is a very effective insecticide, used in plant protection against sucking and chewing insects and leaf miners, and in the hygiene sector against flies. It is highly volatile and therefore also has a fumigant action. It is rapidly hydrolysed in plants to dimethyl phosphate and dichloroacetaldehyde, so that it can also be used shortly before harvest. The oral lDjo for rats is 62 mg/kg. 

The compound is a quick-acting contact and systemic insecticide and, being volatile, it haialso a fumigant action. Both leaves and roots of the plant absorb the compound rapidly. Of its stereoisomers, the Z-isomer (Z-mevinphos, 73a) is a hundred times more active than the -isomer ( -mevinphos, 73b), so that the Z-isomer is virtually the sole carrier of the insecticidal effect. 

Endrin and dieldrin have slightly higher vapor pressures than DDT and were, therefore, slowly volatilized from aqueous solutions (292), soils (282, 292, 294), mud (275, 276), and other surfaces (268, 280, 295, 296). The vaporizing rate of the two compounds was much lower than that of aldrin which has a vapor pressure more than 30 times greater than the others (Table VI). The higher volatility of aldrin was also responsible for its much higher fumigant action than dieldrin or endrin (275, 280, 293, 296). 

Fumigant action of some organophosphorus compounds was related to their vapor pressures and the water content of the soil. Phorate, disulfoton, and dimethoate were equally eflEective in soils in wet years, but only phorate and disulfoton were eflEective in dry years (326). Phorate and disulfoton provided much vapor action in dry years because of their high vapor pressures whereas dimethoate did not. 

Acts as a stomach and contact poison and has some fumigant action... 

Carum carvi L. (Apiaceae) essential oil is able to kill 5. oryzae, and carvone seems to be the active compound against it. (L)-anethole is proven to be effective against R. dominica. Limonene and fenchone, for example, were active against C. pusillus (Lopez et al., 2008). C. copticum C.B. Clarke volatile oil constituents are thymol, a-terpineol, and p-cymene. Especially S. oryzae was weak against the fumigant action of the essential oil, but also mortality on T. castaneum can be observed (Sahafet al, 2007). 

In this bioassay, activity due to contact cannot be distinguished from activity through fumigant action because the containers were sealed. There are two ways to address this problem. The first is to ventilate the chamber to draw off all vapors as is done with a number of pesticide bioassays (e.g., Morse et al. 1986), thus restricting exposure to direct contact. The second simply is to isolate the test semiochemical from physical contact the subjects to that the only means of exposure is by fumigant action. This is illustrated by bioassays of chromenes and benzofurans from Encelia spp. developed by Isman and Proksch (1985) as follows. 

---