Mite reproduction, effects

A recent survey about essential oils and their pure constituents used to control Varroa jacobsoni, contained three interesting tables that reported the toxicity of essential oils for V. jacobsoni and Apis mellifera after 24, 48 and 72 hours in a topical application and in an evaporation test, and the effects of essential oils on behavior and reproduction of V jacobsoni and on the bee brood [63]. The most interesting oils were those of cinnamon and clove, with 100% mite mortality after 24 h and no significant toxicity on honey bees. Furthermore, clove essential oil produced small brood mortality, and it was an inhibitor of mite reproduction. Other effective oils were anise, fennel, lavender, rosemary and wintergreen, which killed 100% mites after 48-72 hours. On the contrary, the oils obtained from garlic, onion, oregano and thyme, were found to be very toxic for honey bees. Among pure constituents, camphor, linalool, linalyl acetate and pinene resulted small brood mortality and inhibited mite reproduction. 

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...

With regard to reproduction, demethylchlordimeform was more active than chlordimeform in decreasing fecundity and egg hatch in spider mites 4-chloro-2-methylaniline also possessed some activity against egg hatch only, while the formanilide was inactive ( 9). Thus it seemed that with chlordimeform the demethyl metabolite played a major role in its effects on spider mite reproduction. However, the results with amitraz and U-44193 were more difficult to interpret. Their common metabolites, BTS-27271, 2,4-dimethylformanilide, and 2,4-dimethylaniline all significantly decreased fecundity and egg hatch, yet U-44193 was one of the most active inhibitors of these processes in mites, and amitraz had no significant effect. Examination of metabolism data (28) revealed that in twospotted spider mites exposed to U-44193 or amitraz, levels of parent compounds were low (<1.0%), but levels of BTS-27271 were several fold higher in mites exposed to... 

Gypsy moth, Lymantria dispar Larvae were fed diets containing 10, 50, 250, or 1250 mg Cu/kg ration from first instar to pupation effects measured on development rate, growth, survival, and reproductive success Oribatid mite, Platynothrus peltifer Fed diets with 13 (control), 28, 64, 168, 598, or 1498 mg Cu/kg DW diet for 3 months... 

The no-observable-effect-concentration (NOEC) for reproduction was 168 mg/kg diet the NOEC for growth was 598 mg/kg. Copper concentrations in whole mites increased significantly at dietary loadings >168 mg/kg... 

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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