RESEARCH NOTE PHOTOTOXICITY OF CITRAL TOTrichoplusia ni(LEPIDOPTERA: NOCTUIDAE) AND ITS AMELIORATION BY VITAMIN A

Abstract

Citral, a monoterpene aldehyde synthesized by several plant families, was recently shown to exhibit ultraviolet A light (320-400 nm) (UVA)-enhanced oxygen-dependent toxicity against bacteria and fungi (Escherichiu coli and Fusarium species). In this study, we report for the first time that citral is phototoxic to insects; at concentrations of 300 ppm in artificial diet, mortality of first instar Trichoplusia ni (cabbage loopers) approached 30% after 120 h of UVA exposure, approximately double the mortality level in the absence of UVA. At 300 ppm, the antioxidant vitamin A reduces citral phototoxicity by about 50% in this species, suggesting that citral phototoxicity against insects is oxygen dependent.

Evaluation of the toxicity of 17 essential oils against Choristoneura rosaceana (Lepidoptera: Tortricidae) and Trichoplusia ni (Lepidoptera: Noctuidae)

“…These tests indicate that diallyl trisulfide and methyl allyl disulfide impart much of the toxicity to garlic oil 30. Citral, the major constituent of lemongrass oil, has been shown to be both toxic and phototoxic against developing T. ni larvae 31. Given that the present sample of lemongrass oil contained 47.1% citral, it is expected that much of the toxicity of lemongrass oil was linked to the presence of citral.…”

Untitled

“…More recently, the importance of the acquisition and maintenance of low-molecular-weight antioxidants as defenses against potentially prooxidant plant allelochemicals has been examined. Antioxidants that have been demonstrated to protect herbivorous insects from photooxidative stress include lutein (Carroll et al, 1997), vitamin A (Green and Berenbaum, 1994), and α-tocopherol (Aucoin et al, 1995). Ascorbic acid and glutathione are believed to be important in the defense against oxidative stress from ingested phenolic compounds (Summers and Felton, 1994;Felton, 1995, 1997;Barbehenn et al, 2001).…”

Phototoxicity of plant secondary metabolites: Insect and mammalian perspectives

“…Moreover, many of the insect studies have examined phototoxic plant compounds from the perspective of developing light-activated pesticides and thus have been tested against insects of little ecological relevance, such as the aquatic larvae of bloodfeeding ectoparasites. The vast majority of studies of effects of phototoxins against ecologically appropriate herbivorous insects have been conducted with artificial diets; with few exceptions (Aucoin et al, 1990;Berenbaum et al, 1991;Green and Berenbaum, 1994), the toxicity of phototoxins when ingested in combination with other plant constituents (including other phototoxins) has not been examined. With respect to mammalian herbivores, again, studies have focused on livestock in confined situations; with one exception (Ashkenazy et al, 19851, a demonstration of avoidance of furanocoumarin-rich shoots of Pituvanthos tviradiatus by the hyrax Prucavia capensis, no studies have been done on herbivorous mammals in natural situations.…”