Search behavior associated with egg cannibalism in Toxorhynchites amboinensis and Toxorhynchites rutilus rutilus (Diptera: Culicidae).

ABSTRACT

Observations based on time-lapse video recordings were used to study behavior associated with egg cannibalism in fourth-instar Toxorhynchites amboinensis (Doleschall) and Tx. r. rutilus (Coquillett). Analysis indicated that, once triggered by finding of the first egg, larvae of both species engaged in a systematic search of the water surface in an attempt to find additional eggs, which were often seized and eaten. Seven behavioral elements were identified in the search repertoire, and their relationships studied by analysis of a matrix of preceding and succeeding behaviors. The pivotal behavior was "sweep-adjust," which accounted for 87.2% of the time budget in Tx. amboinensis and 73.3% in Tx. r. rutilus. Activity in sweep-adjust consisted predominantly of side-to-side sweeps of the head, held just below the surface, punctuated by small forward adjustments of position. Quantitative aspects of the sweep arcs, in terms of angular and linear velocity, were determined for the two species. Eggs encountered during search probably were detected by mechanoreception, only within a very limited, kidney-shaped zone (area approximately 9.8 mm2) centered at the anterior margin of the head. Eggs were seized with the lateral palatal brushes but without head extension as seen in strikes at subsurface prey.