Insecticidal activity of ethanolic extracts of Urginea maritima (L.) Baker bulbs

Abstract

Squill bulbs ( Urginea maritima (L.) Baker) have long been used as a source of natural products with pharmaceutical (cardiotonic) and biocidal (rodenticide) applications, although other biological activities remain to be studied. It has considerable crop potential for semiarid zones but product utilization is negatively affected by variations in toxicity due to genetic and environmental effects. In this paper we studied the insecticidal activity of a group of 24 ethanolic extracts of squill bulbs: 12 wild Spanish populations of different bulb colours with 3 n, 4 n or 6 n ploidy levels extracted either after harvesting or after exposure to indirect sunlight for drying during 30 days. Bioassays were performed using the stored product pest Tribolium castaneum Herbst. Extracts topically applied at 25-day-old larvae, caused a mortality of 60–100% (after 24 h) at doses over 10 μg/insect, although no differences were recorded due to bulb colour, ploidy level, sample origin or light exposure prior to extraction. When extracts were mixed at 10% in the diet, newly hatched larvae showed growth inhibition (3.0–6.2 mm in comparison with 6.5 mm of the control) after 14 days of feeding; extracts from tetra- and hexaploid white bulbs were more active ( P<0.001) than those from triploid red bulbs and an indirect sunlight exposure of the bulbs prior to extraction increased the activity as well.