Exotic aphid species Brachycaudus divaricatae in Central Europe: Distribution, host specificity and molecular diversity

Aphid species Brachycaudus divaricatae Shaposhnikov, 1956, originally described from Turkmenistan and earlier known from the Middle East and Eastern Europe only, is a successful invader to Central Europe. Its principal winter host, Prunus cerasifera , was originally distributed in Central Asia, Near East, and South Eastern Europe. Now it is common in Eastern and Central Europe. Brachycaudus divaricatae is closely related to native European aphid species Brachycaudus lychnidis (L., 1758). The aims of this study were: 1) to summarize and present the information on the distribution and host specificity of B. divaricatae from its invasive area in Europe; 2) to analyse and compare partial sequences of mitochondrial COI with those of nuclear EF-1 α from samples identified as B. divaricatae and B. lychnidis to find possible hybridization or incomplete lineage sorting between these species. Since the first record from Eastern Baltic region in 2002, B. divaricatae changed its distribution area significantly. Now this aphid species has already reached the northern edge of its winter host distribution area. Five COI and 10 EF-1 α haplotypes were detected among the analysed samples of B. divaricatae and B. lychnidis. The most abundant COI haplotype was common for both species. However, EF-1 α sequences were species-specific despite their minor differences. Coalescent simulations were performed using the model assuming no gene flow after the split between species and mimicking the parameters of empirical data. The analysis of genetic distances calculated for simulated data set supported the hypothesis of possible incomplete lineage sorting.