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The Predatory Behavior of Toxorhynchites amboinensis and Tx. brevipalpis Larvae (Diptera: Culicidae) in Response to Subsurface Prey

John R. Linley
The Florida Entomologist
Vol. 73, No. 1 (Mar., 1990), pp. 9-51
DOI: 10.2307/3495328
Stable URL: http://www.jstor.org/stable/3495328
Page Count: 43
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Predatory Behavior of Toxorhynchites amboinensis and Tx. brevipalpis Larvae (Diptera: Culicidae) in Response to Subsurface Prey
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Abstract

Time lapse video recordings and high speed cinematography were used to provide a description and analysis of the predatory behavior of Toxorhynchites amboinensis and Tx. brevipalpis larvae. Only behavior in response to subsurface prey was examined with emphasis on the bending response, in which larvae turn towards approaching prey, and the strike, which effects prey capture. Bending was a very common response and occurred when prey was positioned in any direction relative to the larva's body. Toxorhynchites brevipalpis was more responsive than Tx. amboinensis; Tx. brevipalpis larvae bent more rapidly, towards more distant prey, and through angles representing larger proportions of the prey angle. Bend angle increased with increasing prey angle, but as a proportion of prey angle, bend angle increased as prey angle decreased. Bend angle was little affected by prey distance. Movement during being was smooth and continuous. Each bend consisted of a brief accelerative and longer decelerative phase, with average bending rates varying greatly depending on prey angle and distance. Average bending rate increased with decreasing prey distance, the rate of increase being especially rapid as prey approached close to the body. Prey capture during strikes was accomplished in 0.012-0.024 s, and the entire strike completed in 0.060-0.076 s. Only the lateral palatal brushes were used to capture prey. Immediately after capture, prey was seized by the mandibles and released by the palatal brushes, which played no further role in holding or manipulating food. For descriptive convenience, 3 types of strike were recognized, frontal with head extension, lateral with head extension, and lateral without head extension. These 3 form part of a continuous series. Frontal strikes involved little or no lateral turning towards prey and involved dramatic forward extension of the head, accompanied by opening and closing of the palatal brushes. Head extension was accomplished by sudden increase in the larva's internal pressure resulting from rapid contraction of circular muscles primarily in abdominal segments 1 and 2. Lateral strikes always involved some degree of turning towards prey, and also some degree of head extension when prey was positioned at small angles to either side of the head, but not when prey was at larger angles. Strikes made to larger angles also were accompanied by rotation of the head through approximately 90°, and partial rotation of the thorax. In lateral strikes the degree of angular change during turning was usually greatest between head and thorax, less within the abdomen, and least between thorax and abdomen. Angular velocity and head speed (at the front margin of the head) during the strike varied, in 5 examples filmed, from about 5,000°/s and 210 mm/s, to 12,000°/sec and 600 mm/s. Strikes were made only when prey approached very close to the larva's head. Overall, the proportion of successful strikes for Tx. brevipalpis (71.5%) was significantly higher than for Tx. amboinensis (54.7%). In Tx. amboinensis, but not Tx. brevipalpis, the proportion of successful versus unsuccessful strikes was significantly greater for prey located at smaller angles relative to the head. In both species there was a linear relationship between prey angle and strike angle for both successful and unsucessful strikes, with the successful strike angle averaging about 81% of prey angle in Tx. amboinensis and about 73% in Tx. brevipalpis. /// Se usaron grabaciones de video magnetoscópico contínuo y de cinematografía a alta velocidad para proveer una descripción y un análisis del comportamiento depredador de larvas de Toxorhynchites amboinensis y T. brevipalpis. Solo se examinó el comportamiento como respuesta a la superficie baja de la presa, con las larvas orientándose hacia la presa que se aproxima, y el ataque que efectuó la captura de la presa. Doblarse fue una acción común que ocurrió cuando la presa estaba en cualquier posición relativa al cuerpo de la larva. La captura de la presa durante el ataque se llevó a cabo en 0.12-0.024 segundos, y todo el ataque se completó en 0.60-0.076 segundos. Solo usaron los cepillos laterales palatales para capturar la presa. Inmediatamente después de la captura, la presa fue sujetada por las mandíbulas y soltada por los cepillos palatales, los cuales no tuvieron mas función en aguantar o manipular la comida. Por conveniencia descriptiva, se reconocieron 3 tipos de ataque, frontal con extensión de la cabeza, lateral con extensión de la cabeza, y lateral sin extender la cabeza. Estas tres forman parte de una serie contínua. Ataques frontales involucran poco o ningún movimiento lateral hacia la presa y causa una dramática extensión de la cabeza hacia adelante, acompañado del abrir y cerrar de los cepillos palatales. La extensión de la cabeza se llevó a cabo por un aumento repentino de la presión interna de la larva, causada por rápidas contracciones de los músculos circulares, principalmente de los segmentos abdominales 1 y 2. Los ataques laterales siempre involucraron algún grado de orientación hacia la presa, y también un poco de extensión de la cabeza cuando la presa estaba en posición de ángulos pequeños a cualquier lado de la cabeza, pero no cuando la presas estaba en posición de ánglos mayores. Ataques hechos hacia ángulos mayores también estuvieron acompañados por rotación de la cabeza hasta aproximadamente de 90°, y una rotación parcial del tórax. En ataques laterales, el grado del cambio del ángulo durante la orientación fue usualmente mayor entre la cabeza y el tórax, menos en el abdómen, y menor entre el tórax y el abdómen. La velocidad angular y de la cabeza (al margen frontal de la cabeza) durante el ataque varió, en 5 muestras filmadas, de cerca de 5,000°/s a 210mm/seg, a 12,000°/seg y 600 mm/seg. Los ataques se hicieron solo cuandó la presa se aproximó mucho a la cabeza de la larva. Teniendo todo en cuenta, la proporción de ataques exitosos por Tx. brevipalpis (71.5%) fue significativamente mayor que por Tx. amboinensis (54.7%). En Tx. amboinensis, pero no en Tx. brevipalpis, la proporción de ataques exitosos y no exitosos fue significativamente con presas localizadas a ángulos pequeños relativos a la cabeza. En ambas especies hubo una relación linear entre el ángulo de la presa y el ángulo de ataque en ataques con éxito y sin éxito, con el ángulo de ataque exitoso promediando de 81% del ángulo de la presa en Tx. amboinensis y aproximadamente un 73% en Tx. brevipalpis.

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