Section 8
Chapter 7,925

The predatory behavior of toxorhynchites amboinensis and toxorhynchites brevipalpis larvae diptera culicidae in response to subsurface prey

Linley, J.R.

Florida Entomologist 73(1): 9-51


ISSN/ISBN: 0015-4040
Accession: 007924213

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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 0.012-0.024s, and the entire strike completed in 0.060-0.076s. 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.degree., 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.degree./s and 210 mm/s, to 12,000.degree./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 unsuccessful strikes, with the successful strike angle averaging about 81% of prey angle in Tx. amboinensis and about 73% in Tx. brevipalpis.

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