A Conceptual Model for the Estimation of the Sensitivity of Black Fly Larvae to Bacillus thuringiensis var. israelensis

Abstract

1989. A conceptual model for the estimation of the sensitivity of black fly larvae to Bacildus thuringiewsis var. israelewsis. Caw. 1. Fish. Aquat. Sci. 46: 1785-1 792.Results from bioassays of a commercial formulation sf Baci%%us thuringiensis var. issaelensis (Teknar HP-D) are combined with an empirical model of the feeding rate of larvae sf a target species of black fly (Simuliurn ven~lstcarnl verecundum) to develop a model relating the mortality of larvae to the amount of fsrrnulatisn ingested per unit mass of larvae (specific ingested dose). LD,, sf Teknar HP-D was about 5 pg wet mass sf Teknar per mill igrarn dry mass sf larvae, and independent of size of the larvae and seston concentration. Compared with standard assay analysis relating the mortality to the dose (milligrams per litre times seconds), the proposed mode[ allowed more precise and replicable estimation of the effective dose. Reanalysis sf published data s n the potency sf another Bti formulation (Teknar WDC), confirmed the superiority of the proposed model over the standard procedure. Susceptibility sf larvae to particulate larvicides is mainly a function of the larval feeding rate. In addition to size of the larvae, temperature, and seston concentration, analysis sf the model reveals that the length sf the contact p e r i d and the variability sf feeding rates among individual larvae are important factors determining the mortality rate following treatments. ies auteurs regroupent les rksultats de bis-analyses d'une prkparatisn cammerciale de Baci BBus thuringiensis v. israejensis (Teknar HP-5) et ceux d'un rnodele em~pirique du taux d'ingestion de lames d'une espitce sible de rnouchersn (Simulium venustum/verecundum) afin d'elabarer uw rnodGle etabiissant un rapport entre B e taux de rnsrtalite des larves et la quantite de preparation ingkr6e par unit4 de masse de larves (dose ingeriie specifique).La DL, , du Teknar-B se situe i 3 environ 1 gag de Teknar (masse kurnide) par milligramme de larves (masse s&che) ef est independante de la taille des larves et de la concentration du seston. Par rapport 2 I'analyse type ktablissant un lien entre le taux de mortalit6 et la dose (m@L x s), le m d & l e pr&sent$ permet d'obtenir une estimation de la dose efficace plus precise et facile 3 rkpkter. Une analyse susbkquente de dsnnees publiees riur IPefficacit$ d'une autre prkparation de Bti (Teknar WBC) confirme ia sup6risrite du rnodgle present6 par rapport & la procedure type-La sensibilite des larves aux larvicides solides est surtout fonction du faux d'ingestion. En plus de la taille des larues, de la temperature et de la concentration du sestsn, I'analyse du rnodde rev&le que la dur$e de la p6riode de contact et la variabiIit6 des taux d'ingestion de chaque larve sont d'irnportants facteurs qui influent sur le taux de mortalit6 suite aux traiternenb. (J9930) Susceptibility of larvae to various Bmicides is Betmined eqiricdly from laboratory or field assays. In standard assays (Lacey et al. 1982; Undeen a d Lacey 1982), groups of larvae are exposed to ...