Biology and immature stages of Typopsilopa nigra (Williston) (Diptera : Ephydridae), a secondary consumer of damaged stems of wetland monocots

We investigated the biology and morphology of Typopsilopa nigra (Williston) (Diptera: Ephydridae) from southern California wetlands. Immatures were fo und as secondary invaders of stems of bulrush and cattails tunneled by larv ae of the noctuid moth Bellura obliqua gargantua (Dyar). Adults were taken frequently from stands of California bulrush and cattails. Mating pairs exh ibited tropholaxis immediately after copulation; females laid eggs on decay ing plant fragments in breeding cages. Newly hatched larvae consumed decayi ng lettuce, bulrush, cattails, and other putrid plant materials. Developmen t required 2-3, 2-3, and 3-4 d for instars 1-3, respectively, and the pupal period lasted 6-7 d. The microbial flora associated with decaying plant ma tter probably provided most of the nutrition for larval development. During a choice experiment, newly mated females were offered ovipositional substr ates of decaying bulrush, cattail, sedge, buttercups, and controls (no vege tation); most eggs were, laid during the first several days, and the number s declined over time. Significantly more eggs were deposited on putrefying buttercups than all other substrates despite no evidence of this plant bein g used in nature. We suggest that the semi-liquid medium formed by the rott ing buttercups provided a more suitable moist substrate for oviposition tha n the other treatments. Damaged areas of plants where the immature stages o ccurred were naturally quite moist. These data lead us to hypothesize that nar:ural selection probably acted more heavily on adult ovipositional behav ior than on larval trophic ecology.