Simulium (Gomphostilbia) taitungense sp. nov. is described on the basis of reared adult, pupal and mature larval specimens collected from Taitung, Taiwan. This new species is placed in the ceylonicum species-group within the subgenus Gomphostilbia and is distinguished from related known species by the characteristic colour markings on the ventral surface of the head capsule and on the dorsal surface of the abdomen in the larva. The male of Simulium (Gomphostilbia) tuenense Takaoka, which was originally described from a pharate pupa and a larva, is described for the first time; the association of the adult stage with the larval stage was confirmed by the comparison of the sequences of the mitochondrial 16S rRNA gene; this species is also placed in the ceylonicum species-group.

OBJECTIVESWe studied and compared the possible effects of in utero and lactational exposure to 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) or 3, 3', 4, 4', 5-pentachlorobiphenyl (PCB126) on learning behavior in offspring.

METHODSPregnant Long-Evans Hooded rats were administered either TCDD (50, 200, or 800 ng/kg) or PCB126 (500, 2,000 or 8,000 ng/kg) on gestational day 15. A procedure of schedule-controlled operant behavior was applied to examine learning behavior in the male and female offspring at 11 weeks of age for 30 days. Three indices, namely, response rates in a fixed ratio (FR) and in a differential reinforcement of low rates (DRL), and reward rate in the DRL component in multiple FR 20 DRL 20 s (mult-FR 20 DRL 20-s) test sessions, were used for the evaluation of learning behavior.

RESULTSToxic effects on learning behavior in male and female pups following in utero and lactational exposure to TCDD or PCB126 were observed mainly in the FR learning component. However, no linear dose-dependent effects of either of the two compounds were observed for the above three indices. The response rates of animals in the low-dose TCDD and PCB126 groups decreased and those in medium-dose TCDD and PCB126 groups appeared to induce hyperactive behavior. The high dose of PCB126 appeared to have a distinct toxicity from that of TCDD in terms of the acquisition of learning behavior.

CONCLUSIONSToxicities of PCB126 and TCDD in learning behavior might be similar to each other and the current toxic equivalency factor (TEF) of 0.1 for PCB126 can be considered to be appropriate for this endpoint.