Response of fourth-instar larvae of Anopheles albimanus Wiedemann (Diptera: Culicidae) to food and inert particles floating at the water surface was studied. In a choice test, larvae aggregated at powdered organic materials (blood meal, liver powder, alfalfa flour and wheat flour) but not at inert materials (kaolin, chalk or charcoal). Larvae responded positively to proteins as well as some carbohydrates, but not to cellulose. Retention of larvae at food sources found by random locomotion was found to be responsible for larval aggregation. Larvae ingested food particles 6 -9 times faster than inert particles. The significance of Anopheline feeding behavior in the development of formulations of stomach toxins (bacterial agents) used in larval control is discussed. I J I J J J I lo 2o
ABSTRACT. Drinking rates were determined with four species of freshwater mosquito larvae by colorimetric measurement of the dye ingested after groups of fourth instars were allowed access for set periods to 2% amaranth solutions. The rate of drinking for the saline‐tolerant Aedes aegypti, 309±113 nl per h per individual, was comparable with rates given in the literature for several saline‐water species, but rates for Culex quinquefasciatus, Culex molestus and Anopheles albimanus were markedly lower (167±30, 48±17 and 108±28m per h, respectively). When larvae of A.aegypti and C. quinquefasciatus were glutted with kaolin (allowed to replace all food in the gut by filter‐feeding in kaolin suspension), drinking rates were little affected at first, but after 1 day of fasting (holding in water after glutting), drinking rates were 50% lower and were reduced by a further 20% with fasting for up to 3 days. For A.aegypti, C.quinquefasciatus and C. molestus, drinking rates were approximately doubled with kaolin dispersed in the dye solution, and after fasting, were increased by up to 100% in solutions containing 0.05% of water‐soluble yeast extract. A similar phagostimulant effect of 10‐3M adenylic acid was demonstrated for A. aegypti and C. quinquefasciatus. A single experiment indicated similar stimulatory effects of kaolin and adenylic acid for, A. albimanus. With 0.01‐0.05% agarose in the dye solutions, drinking rates for A. aegypti and C. quinquefasciatus were more than doubled, and a similar though weaker effect was demonstrated for another colloid, methylcellulose. In constrast, both colloids markedly reduced the rate of drinking with A.albimanus. These findings are discussed in relation to whether drinking and filter‐feeding are necessarily coupled. The possible significance of this with respect to larvae that feed in different microhabitats, providing different levels of dissolved and colloidal nutrient organic matter, is considered. The implications of drinking rates for biotests of solubilized bacterial toxins as mosquito larvicides are noted.
Filtration rates of fourth instars of Aedes aegypti L., Anopheles albimanus Wiedemann, Anopheles quadrimaculatus Say and Culex quinquefasciatus Say (Diptera: Culicidae) were determined by quantifying removal rates of suspended latex microspheres or yeast cells. Average filtration rates were 33–34 μl/larva/h (An. quadrimaculatus), 49–55 (An. albimanus), 490–590 (C. quinquefasciatus) or 590–690 μl/larva/h (Ae. aegypti) for larvae exposed to latex beads suspended in phagostimulant yeast extract solutions. In suspensions of yeast cells, filtration rates of Ae. aegypti and C. quinquefasciatus were not significantly different from filtration rates in latex bead suspensions. Larval density, ranging from 0.3 to 2.4 individuals/ml in tests with Ae. aegypti and C. quinquefasciatus and up to 4.8 larvae/ml in tests with Anopheles, did not influence filtration rates. ZUSAMMENFASSUNG Filtrierraten von Stechmückenlarven in Suspensionen von Hefezellen und Latexpartikeln Die Filtrierraten von Viertlarven der Stechmückenarten Aedes aegypti, Anopheles albimanus, Anopheles quadrimaculatus und Culex quinquefasciatus wurden in Laborversuchen bestimmt. Dabei wurde die Filtrierrate definiert als ein Wasservolumen, welches pro Stunde von einer Larve von den Testpartikeln (Hefezellen oder Latexkugeln mit einem Durchmesser von 2 μm) befreit wurde. Nach Exposition der Larven in Dichten zwischen 0.15 und 2.4 Larven/ml (Ae. aegypti und C. quinquefasciatus), oder zwischen 0.6 und 4.8 Larven/ml (Anopheles) wurde der Partikelgehalt der Suspensionen in einem elektronischen Partikelzähler bestimmt. Die Filtrierraten wurden über die Verringerung der Partikeldichte mit zunehmender Larvendichte entsprechend einer in der Literatur angegebenen Formel berechnet. Suspensionen von Hefezellen wurden von Ae. aegypti Larven mit einer Leistung von 680±220 μl/Larve/h gefiltert. Bei Larven von C. quinquefasciatus wurden Filtrierraten von 600±120 μl/Larve/h gemessen. Die Filtrierraten beider Arten waren unabhängig von der Larvendichte. In Suspensionen von Latexpartikeln (zur Phago‐stimulation der Larven wurden diese Partikel in Lösungen von Hefeextrakt angeboten) wurden die folgenden Filtrierraten festgestellt: An. quadrimaculatus: 33–34, An. albimanus: 49–55, C. quinquefasciatus: 490–590, und Ae. aegypti: 590–690 μl/Larve/h. Die Larvendichte hatte auch hier keinen Einfluss auf die Filtrierrate. Hefezellen und Latexpartikel wurden von Ae. aegypti und C. quinquefasciatus mit statistisch nicht signifikant verschiedenen Filtrierraten aufgenommen. Die Filtrierraten der Anopheles Larven waren um mehr als eine Zehnerpotenz kleiner als die Filtrierraten von Culex und Aedes, und auch untereinander signifikant verschieden. Der Einfluss der Filtrierraktivität von Stechmückenlarven auf das Seston der Brutgewässer wird diskutiert.
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