Parasitism efficiency and progeny fitness of Peristenus spretus Chen et van Achterberg vary with nymphal instar of host, Apolygus lucorum (Meyer-Dür)

Peristenus spretus Chen et van Achterberg (Hymenoptera: Braconidae) is the dominant parasitoid of Apolygus lucorum (Meyer-Dür) nymphs (Hemiptera: Miridae) and exerts considerable control of the mirid’s populations in China. To understand developmental fitness of P. spretus in response to host stage selection, the development duration, parasitism efficiency, host handling time, survival rate, offspring size, and sex ratio of the parasitoid were determined when parasitoids were presented with five different instars of A. lucorum. The results showed that the developmental time of P. spretus individuals that parasitized 1st instar nymphs of A. lucorum was significantly longer than that of parasitoids developing in 2nd through 5th instars in no-choice parasitism tests. The sex ratio (as percent female) of P. spretus progeny was not significantly difference among host instars, and the regression between sex ratio (as percent female) and host instar was y  = 9.80 ln ( x ) + 38.12. The best overall performance of P. spretus was observed when wasps parasitized 2nd, 3rd, or 4th instar hosts, because of shorter developmental duration, a higher parasitism rate, more offspring, a higher percent of female offspring, and a larger progeny size (measured as the length of the hind tibia). In choice parasitism test, fitness of P. spretus varied when it was reared in host stages ranging from 1st to 5th instars, and the parasitoid preferred to parasitize 2nd-4th instars. In addition, when parasitizing 3rd−5th instar hosts, parasitoids did not complete their development until their host had molted to an adult. Host body size significantly affected the time required for host capture and parasitization by P. spretus, and the parasitoid required the least time to parasitize medium-sized hosts. The longest handling times of P. spretus were observed for 1st and 5th instar nymphs, with values of 19.8 and 18.3 s, respectively, while the shortest handling time was 13.1 s, for 3rd instars. Our study has provided useful information for the mass rearing of this parasitoid in support of field releases of P. spretus.