TOXICITY OF FRACTIONATED AND DEGRADED MEXICAN MARIGOLD FLORAL EXTRACTTO ADULT SITOPHILUS-ZEAMAIS (COLEOPTERA, CURCULIONIDAE)

Floral extract of Mexican marigold, Tagetes minuta (L.), was toxic to adult male and female maize weevils. Sitophilus zeamais Motschulsky, u nder illuminated and dark conditions. The LD50 values ranged from 35 t o 47 mu g per weevil across sex and photoperiod, whereas LD50 values r anged from 319 to 816 mu g per weevil. Fractionation tended to decreas e toxicity. Generally. both sexes were similarly susceptible to a give n treatment. Although the original extract and certain fractions proba bly contained photoactive thiophenes, which are toxic to certain larva l Lepidoptera, there was no obvious effect of illumination on toxicity for this beetle species. Air exposure for 24 h, in the presence or ab sence of light, greatly reduced the toxicity of the unfractionated ext ract. Chromatographic profiles indicated that fractionation procedures had a significant effect on sample composition and on the amount of n onvolatile material. Air exposure for 24 h had a much more dramatic ef fect, with concomitant 365-nm UVA or incandescent light causing even g reater degradation. Degradation under illumination is the end result o f the process that causes photoactivation in susceptible species. Appa rently. S. zeamais was not adversely affected by the amount of photoac tivation that occurred as the extracts or fractions were degrading und er our test conditions. These results are discussed in terms of of max imizing the central potential of labile material in subsistence agricu lture, particularly when purification is required to remove undesired compounds.