Bias in sex ratios and polyandry rate in reproduction of Leptinotarsa decemlineata

The Colorado potato beetle (CPB, Leptinotarsa decemlineata Slechtd.) is an invasive pest with economic importance worldwide. Sex ratios during egg-hatching and a frequency of polyandry in single-female families were analysed to clarify the reproduction strategy of CPB, which was still known only in fragments. 1296 just hatching 1st instar CPB larvae were collected from 19 single-female families, of which 13 were random families collected from potato fields and 6 were families produced by laboratory farming of naturally fertilised females. All larvae were analysed to detect a sex using a qPCR-based method and to detect polymorphisms in genotypes of 9 microsatellite (SSR) markers. The bias in sex ratio in favour of females was confirmed using linear mixed-effects model in both experimental groups of families: field collections (F = 36.39; P = 0.0001) and laboratory farming (F = 13.74; P = 0.0139). The analysis of diversity in microsatellites proved the polyandry in all progenies as 73% of analysed segregation patterns did not match with the patterns expected for full-sib progenies; on average per locus, 46% of allelic and 49.7% of genotype ratios showed irregular segregation. Both findings contribute toward understanding CPB success rate as an invasive species, as the preferential bearing of females with polyandry has a great potential to keep fitness of progenies, to maintain and operate population diversity, and to accelerate the reproduction of the pest.