Impact of crayfish densities on wet seeded rice and the inefficiency of a non-ionic surfactant as an ecotechnological solution

In order to compare the effects of crayfish (Procambarus clarkii) on rice p roduction, with and without the use of a non-ionic surfactant (Genapol OX-8 0) at a concentration of 0.005%, 12 enclosures at 1 m(2) containment area w ere built in each of two experimental fields. Crayfish densities used in th e experiment were: 0, 1, 3, and 5 adult crayfish per m(-2). In each field, at harvest time, five randomly chosen areas of 1 m(-2) were also sampled fo r rice, infestants and sediment characteristics. Additionally, the number o f filled grains per panicle, the percentage of empty grains and the 100 gra ins weight were determined. One of the experimental fields was used as the treatment (field T) and another one as the control (fit ld C), and no stati stically significant differences (p > 0.05, Mann-Whitney U test) were found between them. No perceptible reduction in crayfish damaging effects was ob served after the use of the surfactant in field T. Results of an ANOVA perf ormed on the effects of crayfish density on rice production at each field w ere statistically significant (p < 0.05). There was a total destruction (10 0%) of rice in the enclosures with densities of 3 and 5 crayfish m(-2). Som e infestant macrophytes survived at 3 crayfish m(-2) in both fields and at 5 crayfish m(-2) in field C. At lower densities (1 crayfish m(-2)) the aver age decrease in grain production attributable to crayfish was 41.61%. Resul ts provided data to calibrate a management model and suggested that the sur factant is not effective in field conditions. (C) 2000 Elsevier Science B.V . All rights reserved.