Mite growth regulatory activity of Blechnum chilense (Kaulf.) Mett

The genus Blechnum has 13 common and well-distributed species in Chile [1]. B. chilense plants have been used for various purposes [1,2]. Tetranychus urticae Koch is highly polyphagous species with 1094 host plant species reported worldwide to date [3]. In this research, we report a phytochemical analysis of B. chilense and its mite growth regulatory effects. From the n-hexane fraction four phytoecdysones were isolated: ecdysone, ponasterone, shidasterone and 2-deoxycrustecdysone. We conducted a bioassay with T. urticae eggs placed on Phaseolus vulgaris L. leaf discs previously treated and the development stage was recorded every 24 hours during thirteen days. All treatments showed statistical significant differences regard to Control in emerged and living adults. The EtOAc fraction at 250 ppm and the n-hexane fraction at 250 ppm and 100 ppm caused the greatest mortality of nymphs and almost the total mortality of the low quantity of adults that emerged (Fig.1). Our results shows that even low concentrations of 10 ppm in both fractions affects the life cycle of T. urticae causing a significant decrease in its population. Studies on the identification and physiological role of ecdysteroids in mites are minimal [4], especially in the order Prostigmata. Our results suggest that early exposure of eggs and larvae to phytoecdysones from B. chilense may interfere in the natural ecdysteroid metabolism in T. urticae leading to the death of nymphs and adults. Our results suggest too that the deaths could be caused by starvation due to the deterrent effects of some phytoecdysones [5,6].