Pyrethrins, cockroaches

Cross-resistance to pyrethroids for outdoor use has developed markedly in M. domestica, mosquitoes, cockroaches, and so on however, it has also been found that natural pyrethrins as well as d-allethrin and prallethrin (ETOC ), which have very similar chemical structures and the same configuration as natural pyrethrins, show an extremely low degree of cross-resistance development by these highly-resis-tant sanitary pests compared to photostable pyrethroids. Many novel synthetic pyrethroids recently developed as household insecticides have tended to pursue efficacy improvements in terms of rapid knock-down effects, residual efficacy or volatility. 

A flushout (FO) test was described by Chadw ick and Evans (1973). The apparatus involved an art ilk in] harbourage from which cockroaches would be expelled into an arena. The distance to which the insects were dispersed and the speed with which this occurred allowed the calculation of FO s in terms of time. Fuchs (1988 commented that the above technique did not necessarily give equal dosing to individual insects. Using his different, though much less realistic. presentation of treated paper discs, he tested a wide range of pyrethroids. Only pyrethrins were examined for dose-efleet and checked for the interaction with PliO which was shown to depress flushout. 

Cochran, D.G, (1987), Effects of synergists on bendincarb and pyrethrins resistance in (he German cockroach (Diuyoptera Blaltidae). J. Ectnt. Entomoi. 80, 728-732. 

Bennett, G.W. and Lund, R.D. (19771. Evaluation of encapsulated pyrethrins (Sectrol" 1 ) for Gentian cockroach and cal flea control. Pest Contnti45, 44—50. 

Commercial formulations using these techniques have extended the residual activity of synergized pyrethrins to German cockroaches under field conditions to 1 month (Bennet and Rea. 1978). This feature, coupled with low mammalian... 

Repellencv. A number of other plant-derived terpenoids have been demonstrated to be repellent to various insects. Many compounds in this class have been proven to be attractants to certain insects (1). Limonene at 1 or 10 mg/box repelled the cockroaches, to the untreated box, in significantly (p<0.05) greater numbers than the 0.001 mg rate or the controls (4). Pulegone and linalool at the 10 mg/box rate repelled significantly more individuals than the 0.0001 mg rate or the controls. Myrcene and a-terpineol did not demonstrate any repellency. Natural pyrethrins were significantly different from the controls at the 0.1 mg/box rate. 

Three other substances were bioassayed for repellency based on their purported household usefulness hedgeapple, bay leaves, and spearmint chewing gum. Figure 2 shows that at the highest exposure rate, the hedgeapple and bay leaves effectively repelled a high percentage of the cockroaches, but were considerably less potent than pyrethrins. 

Repellency of hedgeapple, bay leaves, pyrethrins to German cockroaches. 

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