Desarrollo postembrionario de Latrodectus variegatus (Araneae: Theridiidae)

Abstract

The life cicle of Latrodectus variegatus from cocoons collected in Bariloche, Argentina, is described. In stage IV (first free stage) 361 individually bred spiders were isolated and fed Drosophila melanogaster in the juvenile stage and Musca domestica after wards. "Stage I" is the stage following eclosion. For the study of survival, and average life expectancy, a week was taken as age interval, the first free stage was "age zero". The web is disordered, lacking a nest and located near the ground. The cocoon is pyriform, (similar to L. antheratus), but and with several layers of thread like L. mirabilis. It measures 14-18 mm, close to L. corallinus. The eggs are similar in size to other argentinian Lactrodectus. Each cocoon had a mean of 183 eggs (66% fertile, No=549). In males, the number of moults to maturity is six in 78% of the cases and seven in 22% (similar to L. corallinus and L. antheratus). In females it is seven in 56% of the cases, eight in 39% and nine in 5%. When compared with other argentinian species females L. variegatus appear to be missing one moult. There are two critical periods of mortality: in stage IV, when specimens begin their webs to capture food and in stage VII when the male life cycle ends. The survival curves for several Latrodectus show a high mortality in the first stages of development. Nevertheless, the survival curves of L. variegatus, L. corallinus and L. diaguita share a sharp descent in the first age intervals followed by a gradual decline. This abrupt decrease is not known for L. mirabilis and L. antheratus. The life expectancy at age zero and maximum longevity in L. Variegatus are 17.32 and 73 weeks respectively, 9.01 and 54 in L. mirabilis, 5.36 and 81 in L. corallinus, 14.76 and 100 in L. antheratus and 7.76 and 62 in L. diaguita.