Pest Management Science Pest Manag Sci 61:627–635 (2005 ) DOI: 10.1002/ps.1048 Relationship between biochemical biomarkers and pre-copulatory behaviour and mortality in Gammarus pulex following pulse-exposure to lambda-cyhalothrin Lars-Henrik Heckmann, Nikolai Friberg and Helle W Ravn ∗ National Environmental Research Institute, Vejlsøvej 25, PO Box 314, DK-8600 Silkeborg, Denmark Abstract: The impact of the pyrethroid lambda-cyhalothrin was studied in an in-stream mesocosm placed in a natural riffle of a Danish stream. Twice during summer 2002, the natural macroinvertebrate community was exposed in situ to a 30-min pulse of lambda-cyhalothrin. During exposure, nets caught macroinvertebrates in drift. Exposed and unexposed individuals of the amphipod Gammarus pulex (L) were transferred to aquaria in the laboratory and monitored for biochemical changes (ie biomarkers), pre-copulatory behaviour and mortality. Biochemical biomarkers were identified by screening extracts of exposed and unexposed G pulex using high-performance planar chromatography (HPPC). Biochemical biomarkers were detected 3 h after pulse-exposure, and one biomarker was persistent up to 7 days after exposure. Pre-copulatory behaviour (ie pair formation) was significantly impaired up to 5 days after exposure, and had not fully recovered at the end of the observation period. EC 10 (0.5 h) and EC 50 (0.5 h) values for pre-copulatory behaviour were 0.04 and 0.20 μg litre -1 , respectively. Mortality was significant at 0.35 μg litre -1 with an LC 50 (0.5 h) of 5.69 μg litre -1 . There was a significant relationship between two biomarkers and mortality. The study demonstrated that pulse-exposure at expected environmental concentrations can reduce local populations of G pulex, resulting in severe impact on populations with limited possibilities of re-colonisation.  2005 Society of Chemical Industry Keywords: HPPC; invertebrate; pyrethroid; insecticide; in situ; mesocosm; Gammarus pulex 1 INTRODUCTION Crop protection with pesticides is potentially hazardous to freshwater biota in agricultural areas. Reports of pesticide and residue findings in low- land streams and lakes of agricultural areas are numerous. 1,2 The main routes of pesticide entry from the terrestrial environment to the aquatic environment are by spray drift and run-off. 3 Both routes give rise to short pulses (1 – 2 h) of acute contamination of streams and rivers. 4 In recent decades, lambda-cyhalothrin and other synthetic pyrethroids have accounted for an increasing proportion of the insecticides used in crop protection. Synthetic pyrethroids are lipophilic neurotoxins that are toxic to fish and highly toxic to invertebrates, but relatively harmless to birds and mammals. 5 Following run-off events, maximum concentrations of pyrethroids of 0.66 μg litre −1 have been found in water samples from Danish streams. 6 Field and mesocosm pond studies on the effect of pyrethroids have shown that pesticide stress causes changes at the individual, population and community levels in several crustacean and insect species. 7,8 The amphipod Gammarus pulex (L) is widespread and abundant in streams of Europe. 9 As a shredder it plays a fundamental role in the energy flow and nutrient cycling of lotic food webs. In addition, it produces food (eg faecal pellets) accessible for other stream-dwelling organisms 9 and is important as prey of higher trophic levels, such as the brown trout, Salmo trutta L. 10 Welton 11 estimates that the fish community of Tadnoll Brook, England eats at least 60% of the annual production of G pulex. Several researchers have documented effects of insecticides and other toxicants on behaviour, growth, reproduction and mortality of G pulex. 12 – 14 They show that G pulex is very sensitive to insecticide contamination. However, these are mainly laboratory studies and few have studied effects on G pulex or other stream macroinvertebrates following in situ exposure to an insecticide pulse. 15,16 Neurotoxic interactions, inhibition of enzymatic activity [eg acetylcholinesterase (AChE)] and bio- concentration of pyrethroids have been documented in freshwater invertebrates. 17 – 19 However, changes in the biochemical composition of compounds following ∗ Correspondence to: Helle W Ravn, National Environmental Research Institute, Department of Terrestrial Ecology, Vejlsøvej 25, PO Box 314, DK-8600 Silkeborg, Denmark E-mail: her@dmu.dk (Received 15 June 2004; revised version received 14 January 2005; accepted 10 February 2005) Published online 11 April 2005  2005 Society of Chemical Industry. Pest Manag Sci 1526–498X/2005 /$30.00 627