Mosquito larval consumption of toxic arborescent leaf-litter, and its biocontrol potential

• Published in: Medical and veterinary entomology Vol. 17; no. 2; pp. 151 - 157
• Main Authors: David, J.P, Tilquin, M, Rey, D, Ravanel, P, Meyran, J.C
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01.06.2003; Wiley
• Subjects: Aedes - drug effects; Aedes - physiology; Aedes aegypti; Alnus glutinosa; Animals; Anopheles - drug effects; Anopheles - physiology; Anopheles stephensi; bioassays; Biodiversity; Biodiversity and Ecology; biological control; cellulose; consumption rate; Culex - drug effects; Culex - physiology; Culex pipiens; Culicidae; decomposed leaf litter; detritus; Diet; dose response; Ecology, environment; Environmental Sciences; Feeding Behavior; food intake; France; Global Changes; humin; humine; ingestion; ingestion capacity; insect pests; insecticidal properties; Intestines - physiology; larvae; larval control; larval feeding rate; larval habitat; larvicides; leaf-litter; Lethal Dose 50; Life Sciences; lignin; mortality; Mosquito Control; mosquito larvae; Pest Control, Biological; Plant Leaves - toxicity; plant litter; polyphenols; toxic substances; toxicity; Aedes aegypti • Anopheles stephensi • Culex pipiens • bioassays • biological control • cellulose • consumption rate • detritus • humine • larval feeding rate • ingestion capacity • larval control • larval habitat • larvicides • leaf-litter • lignin • mosquito control • mosquito larvae • polyphenols • France
• ISSN: 0269-283X; 1365-2915
• DOI: 10.1046/j.1365-2915.2003.00432.x

.  Previously we described the mosquito larvicidal properties of decomposed leaf‐litter from deciduous trees, especially the alder Alnus glutinosa (L) Gaertn., due to toxic polyphenols and other secondary compounds. To further examine the biocontrol potential of toxic leaf‐litter for mosquito control, feeding rates of third‐instar mosquito larvae were assessed for examples of three genera: Anopheles stephensi Liston, Aedes aegypti (L) and Culex pipiens L. (Diptera: Culicidae). When immersed in a suspension of non‐toxic leaf‐litter particles (∼0.4 mm), pre‐starved larvae of all three species ingested sufficient material in 30 min to fill the anterior gut lumen (thorax plus two to three abdominal segments). Gut filling peaked after 1–2 h ingestion time, filling the intestine up to six to seven abdominal segments for Ae. aegypti, but maxima of five abdominal segments for Cx. pipiens and An. stephensi. Using three methods to quantify consumption of three materials by third‐instar larvae of Ae. aegypti, the average amount of leaf‐litter (non‐toxic 0.4 mm particles) ingested during 3 h was determined as ∼20 µg/larva (by dry weight and by lignin spectrophotometric assay). Consumption of humine (∼100 µm particles extracted from leaf‐litter) during 3 h was ∼80 µg/larva for Ae. aegypti, but only ∼30 µg/larva for Cx. pipiens and 15 µg/larva for An. stephensi, with good concordance of determinations by dry weight and by radiometric assay. Cellulose consumption by Ae. aegypti was intermediate: ∼40 µg/larva determined by radiometric assay. Apparent differences between the amounts of these materials ingested by Ae.aegypti larvae (humine four‐fold, cellulose two‐fold more than leaf‐litter) may be attributed to contrasts in palatability (perhaps related to particle size or form), rather than technical discrepancies, because there was good concordance between results of both methods used to determine the amounts of humine and leaf‐litter ingested. Bioassays of toxic leaf‐litter (decomposed 10 months) with 4‐h exposure period (ingestion time) ranked the order of sensitivity: Ae. aegypti (LC50 < 0.03 g/L) > An. stephensi (LC50 = 0.35 g/L) > Cx. pipiens (LC20 > 0.4 g/L). When immersed in the high concentration of 0.5 g/L toxic leaf‐litter (0.4 mm particles), as little as 15–30 min ingestion time (exposure period) was sufficient to kill the majority of larvae of all three species, as soon as the gut lumen was filled for only the first few abdominal segments. Possibilities for mosquito larval control with toxic leaf‐litter products and the need for standardized ingestion bioassays of larvicidal particles are discussed.