Electrophysiological responses of gustatory sensilla on the ovipositor of the parasitoid Diachasmimorpha longicaudata (Hymenoptera: Braconidae).

DEVESCOVI, FRANCISCO; VAN LOON; DF SEGURA

Congreso; 9th Meeting of Tephritid Workers of the Western Hemisphere; 2016

Diachasmimorpha longicaudata is a solitary endoparasitoid that attacks Tephritidae fruit fly larvae whilst they are feeding inside the fruit. Therefore, it is likely that assessment of host parasitization status is based on sensory input from the ovipositor. Host discrimination ability has been demonstrated through behavioural studies. Nonetheless, superparasitism (oviposition in a parasitized larva) is frequently observed. Since supernumerary larvae do not develop into adult parasitoids, this phenomenon is considered a limitation for mass rearing. Here, we evaluated electrophysiological responses of gustatory sensilla on the tip of the paired ovipositor valves. Haemolymph of parasitized or unparasitized Ceratitis capitata larvae was used as stimulus and physiological saline (PBS) was used as control. The female parasitoid abdomen was connected to a DC amplifier and glass capillary containing the stimulus or PBS was connected to ground. Neuronal activity recording started automatically when the capillary contacted a single gustatory sensillum. Spike frequencies were compared between treatments by means of ANOVA. Scanning electron microscopy (SEM) was performed to corroborate the presence of these gustatory sensilla. No differences were found in the frequency of spikes among the stimuli. PBS elicited almost no response. Adaptation was observed, given that 100 ms after stimulus onset an abrupt decrease in activity was recorded, followed by an almost constant firing rate. SEM pictures showed a low density of gustatory sensilla on the tip of each paired valve allowing single sensillum recordings. The firing pattern and previous ultrustuctural studies indicated that the sensilla under study are enervated by only one chemosensory neuron. The electrophysiological recordings showed that the stimulated neurons did not detect chemical differences associated to host parasitization status. Further studies on sensilla of different valves of the ovipositor of D. longicaudata are needed to evaluate the role of dissolved chemical cues in host status assessment.