Preference and life history traits of Aphelinus abdominalis (Hymenoptera: Aphelinidae) when offered different development stages of the lettuce aphid Nasonovia ribisnigri (Hemiptera: Aphididae)

The degree of parasitisation, host feeding, developmental time, adult emergence and female sex ratio of the parasitoid Aphelinus abdominalis were evaluated when different host stages of N. ribisnigri (1st, 2nd, 3rd, alatoid 4th instar or newly moulted apterous adult) were offered as hosts under no-choice conditions in the laboratory at 22 °C, 70 % RH and 16:8 L:D. In addition, the parasitoid preference between 2nd and alatoid 4th instar was examined. In the no-choice experiments, the highest degree of successful parasitisation (leading to mummy formation) (41–56 %) was observed when young and intermediate stages of the lettuce aphid were exposed for parasitism compared with older developmental stages. This pattern was supported in the choice experiment where significantly more 2nd instar lettuce aphids were parasitised than alatoid 4th instars, with Manly’s preference index (mean ± SE) for the former stage being 0.79 ± 0.03. Incomplete parasitisation was recorded highest in 1st instar (mean ± SE: 29.95 % ± 4.71), with much lower values (1–8 %) attained in the 2nd, 3rd, alatoid 4th instar and apterous adult with no significant differences. Host feeding was low (2–4 %) and only recorded in 1st and 2nd instars. The mean development time of A. abdominalis from egg to adult emergence was longest for 1st instar (19.03 ± 0.12 days) and the shortest for apterous adults (16.59 ± 0.29 days). A high percentage of adult emergence (>80 %) from mummified aphids as well as a strongly female-biased sex ratio (>78 %) were found across all host stages of the lettuce aphid.