The ladybird, Serangium japonicum (Coleoptera: Coccinellidae), is one of the most important predators of whiteflies in China, however, the suitability of different kinds of prey and nutritional requirements of this predator are poorly studied. The objectives of the present study were to investigate the pre-imaginal development, percentage survival of immatures, adult longevity and fecundity of S. japonicum when reared on two different species of prey, mixed ages of the cotton whitefly Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) biotype-B (i.e., eggs and nymphs) and green peach aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) in order to quantify their relative suitability as prey under laboratory conditions of 25 ± 1°C, 50 ± 10% RH and a photoperiod of 16L : 8D. The results of this study indicate that the total developmental period (from egg to adult) was shorter when they were fed on B. tabaci (18.29 ± 0.13 days) than on M. persicae (19.85 ± 0.22 days). The percentage survival of the immatures, growth index, development rate, adult fresh weight, fecundity and percentage of eggs hatching were higher and the pre-oviposition period was significantly shorter when S. japonicum were fed on B. tabaci than on M. persicae. In contrast, there was no significant difference in their longevity and oviposition period when fed on B. tabaci and M. persicae. The results indicate that as a diet for S. japonicum M. persicae is inferior to B. tabaci. This is the first record of S. japonicum being able to complete its development feeding exclusively on M. persicae. Since B. tabaci and M. persicae often simultaneously occur in vegetable fields, these results indicate that it is likely that S. japonicum could be utilized to control mixed populations of aphids and whiteflies, and furthers our understanding of ladybird population dynamics in the field in relation to the availability of different species of prey.
The relative suitability of three prey organisms, Bemisia tabaci (Gennadius) eggs, B. tabaci nymphs, and Myzus persicae (Sulzer), to the ladybird Propylea japonica (Thunberg) was evaluated under laboratory conditions. The larvae developed fastest when fed M. persicae, and slowest on B. tabaci eggs. When fed M. persicae, all larvae successfully developed into adult with a growth index (i.e., percent pupation/larval period in days) of 13.16 and development rate of 0.096. The longevity of starving adults was 4.7 ± 0.2 days. In contrast, when fed B. tabaci eggs, all larvae survived to the second instars, 56.7% of which survived to the third instars, 13.3% to the fourth instars; only 6.7% of larvae survived to the pupal stage and the pupae developed into abnormal adults that died shortly. When fed B. tabaci nymphs, all larvae survived and successfully developed into adults with a growth index of 10.71 and development rate of 0.083. The adult body mass was greater when larvae fed M. persicae, compared to adults eclosing from larvae fed B. tabaci nymphs. On the basis of these findings, the order of suitability of three prey organisms for P. japonica is M. persicae > B. tabaci nymph > B. tabaci egg. This is the first record that P. japonica can complete its development when feeding exclusively on whitefly nymphs.