Mite reproduction, effects formamidines

The procedures for examining the effects of formamidines on twospotted spider mite reproduction were similar to those for dispersal mentioned above with the following exception. After the treated leaflets had dripped dry, the surviving mites were transferred to untreated leaf discs. This initial transfer was made to minimize potential residual activity and to ensure that formamidine effects on reproduction were due to the treatment applied to the adult female mites. Under these conditions, there should be little, if any, direct ovicidal action or mortality of... 

A correlation matrix for the effects of formamidines on twospotted spider mite reproduction and mortality is shown in Table VI. Highly significant relationships existed among the effects of formamidines on fecundity, egg hatch, and reproductive potential, whereas only weak associations were found between these parameters and formamidine-induced mortality (19). 

To explore this further, a demographic study was conducted with chlordimeform, amitraz, and compound 17, which was the most active mite reproduction inhibitor among the nonlethal formamidines (20). Each of the three formamidines caused a reduction in survivorship and fecundity which resulted in a significant decrease in the intrinsic rate of increase of the mite population. In these experiments, amitraz was most potent, chlordimeform was intermediate, and compound 17 was least potent (20). This apparent disparity between the strong activity of chlordimeform and amitraz on mite reproduction at the population level and their weak activity at the individual level can be explained as follows. The effects of amitraz on population growth were due mainly to its lethal activity to the various life stages, and the effects of chlordimeform were due to its lethality to life stages as well as its reduction of fecundity. The activity of compound T7 resulted only from its reduction of fecundity (20). 

Table VI. Correlation Matrix for the Effects of Formamidines on Twospotted Spider Mite Reproduction and Mortality at 72 Hours...

These in vitro and in vivo investigations indicate that chlordimeform as well as other formamidines and formanilides can interfere with biogenic amine regulatory mechanisms in bulb mites. Whether these actions are related to any of the formamidine effects on mite dispersal and reproduction remains to be demonstrated. 

The studies discussed herein show that formamidines without the conventional lethal moiety can elicit dispersal behavior and can interfere with reproduction in twospotted spider mites. Walk-off dispersal elicited by formamidines was correlated with formamidine-induced mortality. Since these structure-activity relationships of formamidines are similar to those for pertubation of octopa-minergic transmission in insects, a similar mechanism could be involved in these actions in mites. Since structure-activity relationships for formamidine effects on spin-down and reproduction were not correlated with those for lethality, other mechanisms, which may or may not involve octopamine or other biogenic amines, are probably associated with these actions. 

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