Effect of diet and mating status on ovarian development and oviposition in the polyphagous predator Macrolophus caliginosus (Heteroptera: Miridae)

The mirid bug Macrolophus caliginosus is commercially reared on eggs of Ephestia kuehniella, constituting an effective but expensive factitious food. Artificial diets can decrease the rearing costs of this natural enemy, but developing and evaluating an artificial diet is a very time-consuming activity. In the current study, development and reproduction of M. caliginosus on two artificial diets based on egg yolk were investigated. The artificial diets resulted in longer development and lower adult weights, but survival was comparable with that of control insects fed E. kuehniella eggs. Reproductive potential of the predator reared on factitious and artificial foods was assessed using a dissection method. The influence of nymphal food on fecundity was less important than that of adult food. Adults fed E. kuehniella eggs had a preoviposition period of about 4 days, whereas adults offered only plant material started laying eggs about 7 days after emergence. Ovarian scores at day 7 were higher for females fed E. kuehniella eggs than for those given access only to a tobacco leaf. Ovarian scores were not significantly affected by mating status. In a final test, a parallel comparison of two methods for assessing reproductive response to diet was made. Here, adult couples were offered one of four diets: E. kuehniella eggs, one of two artificial diets or no food. Half of the females were dissected and the other half was held for determining lifetime oviposition. Females fed E. kuehniella eggs had superior ovarian scores and laid more eggs than those fed either artificial diet or those given no extra food. A good correlation (r = 0.97) was obtained between ovarian scores and oviposition data, indicating that dissecting females after 1 week provides a reliable estimate of fecundity as affected by diet quality. Rapid reproductive assessments as used in the current study will help to increase the rate of development of artificial diets and may contribute to more cost effective production methods for augmentative biological control agents.