Larvae dispersal

Hurst (19) discusses the similarity in action of the pyrethrins and of DDT as indicated by a dispersant action on the lipids of insect cuticle and internal tissue. He has developed an elaborate theory of contact insecticidal action but provides no experimental data. Hurst believes that the susceptibility to insecticides depends partially on the cuticular permeability, but more fundamentally on the effects on internal tissue receptors which control oxidative metabolism or oxidative enzyme systems. The access of pyrethrins to insects, for example, is facilitated by adsorption and storage in the lipophilic layers of the epicuticle. The epicuticle is to be regarded as a lipoprotein mosaic consisting of alternating patches of lipid and protein receptors which are sites of oxidase activity. Such a condition exists in both the hydrophilic type of cuticle found in larvae of Calliphora and Phormia and in the waxy cuticle of Tenebrio larvae. Hurst explains pyrethrinization as a preliminary narcosis or knockdown phase in which oxidase action is blocked by adsorption of the insecticide on the lipoprotein tissue components, followed by death when further dispersant action of the insecticide results in an irreversible increase in the phenoloxidase activity as a result of the displacement of protective lipids. This increase in phenoloxidase activity is accompanied by the accumulation of toxic quinoid metabolites in the blood and tissues—for example, O-quinones which would block substrate access to normal enzyme systems. The varying degrees of susceptibility shown by different insect species to an insecticide may be explainable not only in terms of differences in cuticle make-up but also as internal factors associated with the stability of oxidase systems. 

Barbehenn R (2001) Roles of peritrophic membranes in protecting herbivorous insects from ingested plant allelochemicals. Arch Insect Biochem Physiol 47 86-99 Barbehenn RV, Martin MM (1998) Formation of insoluble and colloidally dispersed tannic acid complexes in the midgut fluid ofManduca sexta (Lepidoptera Sphingidae) an explanation for the failure of tannic acid to cross the peritrophic envelopes of lepidopteran larvae. Arch Insect Biochem Physiol 39 109-117... 

Natural budworm densities were determined by sampling 6 sprays, each 40 cm long, In the same quarter of the tree used to collect tissue for chemical analysis and to collect defoliation data. Densities were expressed as the average number of budworm larvae per 100 buds per tree. A visual estimate of the amount of defoliation eilso was made In the same area of the crown where the densities and needle tissue were collected. Since budworm may disperse from heavily defoliated trees, (Greenback, 1963) budworm densities from each tree were weighted by the level of defoliation that each tree sustained. This resulted In an Infestation Intensity measurement (dependent variable) which was subjected to multiple stepwise correlation analysis using various foliage quality and physical tree parameters as the Independent variables. Thirty-one parameters were used as Independent variables In this analysis. 

Finally, a distinction must be made between developing embryos and fully formed larvae, since the tolerance may be different. If the growth of a fully developed larva is retarded, it could prolong the pelagic life stage and promote loss through predation, disease and dispersion. 

Toxicity of Dispersed and Undispersed Prudhoe Bay Crude Oil Fractions to Shrimp, Fish and Their Larvae... 

Malathion shows a relatively high toxicity to fish, Morphological abnormalities in African catfish larvae exposed to malathion were observed (Lien ei al., 1997). Diazinon has no hormone-like activity but shows endocrine-disrupting potential in fish. In dispersed adrenocortical cells of rainbow trout, this compound suppressed cortisol secretion in response to ACTH in vitro (Bisson and Hontela,... 

---