Reproductive biology of Philaenus spumarius (Hemiptera Aphrophoridae)

The meadow spittlebug Philaenus spumarius is the main vector of Xylella fastidiosa Wells in Europe and, namely, of X. fastidiosa subsp. pauca, causal agent of the Olive Quick Decline Syndrome (OQDS) in the Apulia Region of Italy. The phenology and host plant association of P. spumarius nymphs and adults in different geographical areas have been described. However, the reproductive biology is still largely unknown and must be studied in depth to design efficient control strategies for this vector species in the areas where X. fastidiosa is present. To fill the existing knowledge gaps, different studies were carried out with insect rearings and laboratory analyses. Fecundity was investigated under controlled conditions by counting the egg numbers and of nymph progeny , using both single couples and groups of insects. The ovarial parapause length was studied by ovarian egg counting and analysis of the expression level of the Vitellogenin gene (Vg) during different phases of female adult life. Finally, several spittlebug populations from different areas and environmental conditions were screened for the presence of Wolbachia. Fecundity was evaluated for females collected in different sites of Northern Italy and Apulia (Southern Italy). The average number of eggs produced by single females ranged from 18 to 196, highly variable according to the geographic origin of the population and the methodology used for the trials. The ovarial parapause was confirmed for all the spittlebug populations, although with important differences due to altitude and latitude. The females of Alpine populations, collected above 1,500 m a.s.l. showed early development of ovarian eggs and increased levels of Vg expression as early as 2-3 weeks after their emergence. The spittlebugs collected in lowlands of Northern Italy and Apulia Region, started to develop eggs in the ovaries, and showed increased level of Vg expression from the beginning of September and October, respectively. Therefore, females started to mature eggs 4-5 months after their emergence. The expression of Vg was a very reliable marker of ovarian development and could be used to estimate the end of the parapause and the beginning of egg maturation and laying phases. The spittlebug specimens collected at the alpine sites were infected at high percentage (67%) by Wolbachia, a much higher frequency compared to that of one population collected at lowlands. Overall, the results indicate that egg production is strongly influenced by environmental conditions and by the period when parapause is overcome. Thus, P. spumarius populations were regulated by environmental conditions. The role of Wolbachia in the biology of the spittlebug is still unknown, but these symbionts may play an important role in the adaptation of the insect to cold areas, with very short warm seasons required for reproduction. These findings support the role of Wolbachia as reproduction manipulators.