Olfactory behavior of Philaenus spumarius (Hemiptera: Aphrophoridae) to two naturally occurring volatile compounds on almond, olive, and vine leaves

Olive groves, almond orchards, and vineyards are characteristic elements of the landscape in the Mediterranean basin. Currently, these crops are threatened by the vector-borne plant pathogen Xylella fastidiosa, which is rapidly transmitted and spread by insect vectors, such as Philaenus spumarius, the main vector in Europe. Understanding the olfactory response of P. spumarius is of outmost importance since the response to chemical signals in the environment can affect insect survival and reproduction, eliciting attractive or aversive behavior. In this work, we aimed at evaluating the olfactory response of adults of P. spumarius to two volatile compounds common in almond, olive, and vine leaves. For this, the volatile profile of each crop was assessed by headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC/MS). The volatile compounds cis-3hexenyl acetate and cis-3-hexen-1-ol are present in all the crops. The behavioral responses to the volatile compounds were assessed by recording individually 30 Individuals of both sexes of P. spumarius for 20 min in a four-arm olfactometer. The volatile compounds were tested at 5, 10, 20, 30 µg/µL and a stream of purified air and sunflower oil were used as controls.  At the lowest concentration, females and males were significantly attracted by the two volatile compounds (P<0.01). Moreover, they showed a higher frequency of visits and a longer permanence in the areas with cis-3hexenyl acetate and cis-3-hexen-1-ol.  However, when the individuals were exposed to the volatile compounds at 10 µg/µL, females chose more often the stream of purified air (P<0.01), whereas the males presented no significantly differences in their choice (P= 0.093).  At the highest concentrations, no significantly differences were detected among treatments. Low concentrations of these volatiles may attract P. spumarius, however, higher concentrations can saturate the olfactory sensilla affecting the choice.