Are we analysing knockdown in the right way? How independence of the knockdown-recovery process from mortality may affect measures for behavioural effects in pesticide bioassays

Abstract

: In pesticide bioassays, especially those with neurotoxic agents, eþ ects on animals are typically grouped into classes according to behaviour, such as normal and aþ ected behaviour, which may range from unstable walking behaviour, to unable to move, to mortality. Generally, recovery is observed in all these eþ ect classes, except the last. Mortality, however, disturbs the analysis of the recovery processes because it decreases the number of animals that otherwise could have shown a reversible eþ ect. We consider that this interaction between mortality and other, reversible, eþ ects is a conceptual problem, and give arguments in favour of analysing changes in behaviour and mortality as two independent, simultaneously occurring neurotoxic syndromes. As an illustration, two data sets are analysed in both ways and these show that marked diþ erences may exist between conclusions reached by the two viewpoints. The consequences thereof are discussed in relation to toxico-kinetic explanations for neurotoxicant eþ ects on behaviour and mortality.

Morbidity and recovery of the Pacific Coast wireworm, Limonius canus, following contact with tefluthrin‐treated wheat seeds

“…Recovery from temporary morbidity is an important component of pyrethroid action (Alzogaray & Zerba, 1997), and has been reported in Diptera (Sawicki, 1962;Adams & Miller, 1980), Blattaria (Gammon et al, 1981;Benoit et al, 1985), Homoptera (Alzogaray & Zerba, 1997), Lepidoptera (Toth & Sparks, 1990), Coleoptera (Arthur, 1999), as well as in annelids (Roshon, 1998). Pyrethroid 'knockdown' is usually rapid in onset, may be long lasting, but does not necessarily lead to mortality (Naumann, 1990), illustrating the importance of differentiating between knockdown and mortality (Jagers op Akkerhuis et al, 1999). The results presented here provide further evidence that initial morbidity of wireworms is a poor indicator of the overall efficacy of an insecticide, as wireworms are often capable of making a full recovery .…”

Recent insights into sublethal effects of pesticides on insect respiratory physiology

“…21 Increasing metabolic rate leads to an increase in water loss rate. 22,23 Insects often endure shorter or longer periods of immobility because of their developmental stage, unfavorable environmental conditions, [23][24][25][26][27] paralysis due to contact with toxicants, 28,29 or death feigning for protection 15,30,31 during which it is important to decrease water loss rate to avoid desiccation.…”

Selectivity Assessment of Chlorfenvinphos Reevaluated by Including Physiological and Behavioral Effects on an Important Beneficial Insect

“…Since both sexes were submitted to a LD10 application, these differences are probably not related to a sexual difference in sensitivity. In a recent study, Jagers op Akkerhuis et al [37] suggested that behavioral symptoms occurring within the first hours after a topical treatment may be separated into two phases, depending on diffusion of the toxicant in insects. In the first phase, which starts within a few minutes after the treatment, insects respond to a peripheral action of the insecticide, which concerns the nerves located just below the body area where the insecticide was applied.…”