3.1.4. Exploration of sub-lethal poisoning

The link between the dose-lethality relation in laboratory conditions and the acute toxicity in field conditions is neither direct nor simple, nor can it be blindly guided by the “useful rule of thumb way of determining the anticipated toxicity hazards of a pesticide to honey bees in the field” (Atkins et al., 1973). For example, this rule stipulates that “since the LD50 of parathion is 0.175 µg/bee, we would expect that 0.17 lb/acre of parathion would kill 50% of the bees foraging in a treated field crop at the time of the treatment or shortly afterwards”, without mentioning the possibility of sub-lethal toxicity. So the following question remains: can the sublethal toxicology be deduced from the dose-lethality relation?

In the log-probit model itself, the extreme values of the dose-% lethality relation cannot be derived from the LD50 and the slope of the regression line (Robertson et al., 1984). Moreover the log-probit model is not necessarily the most adapted model for the dose-lethality relation. For the lowest LD values, the log-probit model is questioned by Calabrese (2005), who mentioned the frequency of the hormesis phenomenon, that is “a modest treatment-related response occur(ing) immediately below the No Observable Effect Level”. Consequently, special designs are needed to estimate the low doses effects.

In this complex domain, mortality is not the best criterion for determining toxic effects. During its adult life, the worker bee must be physically able to fly and has to use functional short and long term memories to communicate, care the larvae, form the winter cluster and perform many other social functions. Thus a panel of markers of behavioural, physiological, and molecular origins can provide substantial information in matter of sub-acute poisoning (Desneux et al., 2007). Each sublethal individual assay is important so one can know if the adult bees are capable of accomplishing one of the activities essential for perpetuating the bee colony and maintaining its ecological role (Brittain and Potts, 2011).