## 3 Results and Discussion  
### Development of Earthworms in the Different Biomixtures  
In the non-contaminated biomixtures (NP and NO) at week two, more than 50% of the non-clitellated earthworms, had migrated from the horse manure to the biomixture, reaching 100% at week six of vermicomposting (Figure 1). The mean of the individual weight of alive earthworms in non-contaminated biomixtures diminished slightly from \(308\pm 33\) mg earthworm\({}^{-1}\) in NP and \(357\pm 10\) mg earthworm\({}^{-1}\) in NO at the second week, to \(251\pm 5\) mg earthworm\({}^{-1}\) in NP and \(298\pm 11\) mg earthworm\({}^{-1}\) in NO at the sixth week (Figure 2). In the NP biomixture, all earthworms lacked a developed clitellum, whereas in NO biomixture, 15% reached sexual maturity at week four. As a consequence, three new hatched earthworms appeared at week 10 in the NO biomixture. At the end of the experimental period, the percentage of earthworms diminished slightly, due to the death of some earthworms inhabiting both biomixtures. The remaining earthworms showed lower weights (\(210\pm 40\) mg earthworm\({}^{-1}\) in NP and \(245\pm 22\) earthworm\({}^{-1}\) in NO) and none of them had a clitellum. The loss of weight and the presence of a clitellum only in the 15% of the earthworms in the NO biomixture reveal the limited feasibility of the two non-contaminated biomixtures to be used in vermicomposting processes. This might be due to the fact that both mixtures are constituted by soil (25%), stable organic materials (peat or vermicompost, 25%) and lignocellulosic organic wastes (straw or pruning, 50%), which could not ensure adequate nutritional resources for the optimal growth and reproduction of the epigec earthworm used in this experiment [28]. Therefore, the population dynamics observed in those biomixtures were different from that recorded in traditional vermicomposting processes using substrates composed only of raw organic wastes [8]. At week six, more than 70% and 50% of the non-clitellated earthworms, inoculated in the horse manure colonized the contaminated biomitxtures CP and CO, respectively (Figure 1). Their individual weights were significantly lower (138 \(\pm\) 10 mg earthworm\({}^{-1}\) in CP and 114 \(\pm\) 17 mg earthworm\({}^{-1}\) in CO) than those recorded in the non-contaminated biomitxtures, and, none of the earthworms had a clitellum (Figure 2). The number of earthworms diminished significantly after six weeks and finally most of them died remaining only a 17% with very low weight, \(72\pm 13\) mg earthworm\({}^{-1}\) in CP and 97 \(\pm\) 13 mg earthworm\({}^{-1}\) in CO. The low weight and the death of most of the earthworms suggest that the residuals-contaminated biomitxtures are not suitable habitats for the earthworm population due, mainly, to the high concentration of pesticide residues remaining in the contaminated biomitxtures  
Figure 1: Percentages of earthworm colonization in the non-contaminated (NP and NO) and contaminated (CP and CO) biomitures at each vermicomposing time. Error bars represent the standard deviation (n = 3). Different letters indicate significant differences between biomitures (\(p<\) 0.05) at each vermicomposing time. Figure 2: Evolution of the individual earthworm weight in the non-contaminated (NP and NO) and contaminated (CP and CO) biomitures at each vermicomposing time. Error bars represent the standard deviation (n = 3). Different letters indicate significant differences between biomitures (\(p<\) 0.05) at each vermicomposing time. (Table 1). Besides, imidalcoprid is a toxic neonicotinoid insecticide for _E. fetida_[29], which can also be an important factor contributing to the negative effects observed on the earthworm population. Those concentrations exceeded largely the 14 day lethal concentration 50 (LC50) value established for _E. fetida_ in an artificial soil test at 10.7 mg kg\({}^{-1}\) of imidalcoprid [30]. [PERSON] et al. [31] observed, after 14 days, non-survival _E. fetida_ earthworms in an artificial soil exposed to 3.78 mg kg\({}^{-1}\) of imidalcoprid.