Use of natural pyrethrum to control the red swamp crayfish Procambarus clarkii in a rural land of Italy.

BACKGROUND: The red swamp crayfish, Procambarus clarkii (Girard, 1852), inflicts severe ecological and economic damages in Europe. With the aim of developing an efficient and safe method for the control of this species’ invasive populations, we carried out four experiments that assessed the impact of natural pyrethrum (i.e. Pyblast) on crayfish and on the environment in a rural land of Northern Italy, as follows. Experiment 1: we quantified 24-h LC100 and LC50 on crayfish; Experiment 2: we assessed the time of breaking down 24-h LC100 using Daphnia magna as a bioindicator; Experiments 3 and 4: we investigated the effects of 24-h LC100 on crayfish by applying the biocide into burrows and in an experimental tract of a canal, respectively. RESULTS: Pyblast concentrations of 0.05 and 0.02 mg litre-1 corresponded to 24-h LC100 and LC50, respectively. The concentration of 0.05 mg litre-1 broke down after 72 h, whereas 0.02 mg litre-1 did not cause any significant mortality in D. magna after 24 h. However, 0.05 mg litre-1 had no effect on crayfish when it was introduced into the burrows, whereas, if applied in the water, led to the total mortality of crayfish. CONCLUSION: we provide experimental proofs about the efficacy of using Pyblast to control invasive crayfish populations. Obviously, before its use on large scale, further studies are needed to assess its potential effects on non-target species.