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

SEGURA; DEVESCOVI, FRANCISCO; MARIANA M. VISCARRET; BACHMANN; CLADERA; VAN LOON

Congreso; IX Congreso Argentino de Entomología; 2015

SEA

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 coming from the inner valves of the ovipositor, which are inserted into concealed hosts for oviposition. Host discrimination ability has been demonstrated through behavioral 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 (0hs or 24hs after parasitization) or unparasitizedCeratitis capitata larvae were used as stimuli. Physiological saline (PBS) was used as control. The female parasitoid abdomen was connected to a DC amplifier (TasteProbe + IDAC, Syntech, NL) and a 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 on the stimulated valves.No differences were found in the frequency of spikes among the stimuli (ANOVA: F(2,40) = 0.142; P = 0.868). In every case, a classical response of a phasic-tonic neuronwas observed, given that an abrupt decrease in the firing rate after the first 200 ms of stimulus onset was recorded, followed by a slowly decreasing activity. PBS elicited almost no response.SEM pictures showed a low density of gustatory sensilla(confirmed by the presence of one pore per sensillum) on the tip of each paired valve allowing single sensillum recordings. The firing pattern and previous ultrastructural 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 the unpaired valve of the ovipositor or other ways to obtain these or other stimuli are needed to evaluate the role of dissolved chemical cues in host status assessment. Nevertheless, stimulation at the peripheral level may not be sufficientto evidence this behavior and the integration of other internal and external cues at different ganglions or brain may be needed.