EVIDENCE FOR ARRESTED DEVELOPMENT OF ABOMASAL NEMATODES IN WHITE-TAILED DEER

White-tailed deer (Odocoileus virginianus) obtained from Noxubee Natio nal Wildlife Refuge, Noxubee County, Mississippi (USA) during April (n = 3), June (n = 5), September (n = 5), and November (n = 5) 1989, wer e necropsied for counting and identification of adult and larval stage s of abomasal nematodes. Fourth-stage larvae (L4) (n less-than-or-equa l-to 25) from each deer were randomly selected for measurement of tota l worm length and width. Adults of four worm species were found: Mazam astrongylus odocoilei, M. pursglovei, Ostertagia mossi, and O. dikmans i. There were no differences between months in adult male worm burdens for all species except O. dikmansi for which the April worm burden wa s greatest (P less-than-or-equal-to 0.05). Overall, the length of L4 r anged from 929 to 4,361 mum. There were no significant differences (P > 0.05) between months in the mean length (1,334 to 1,532 mum) of L4. Except for low numbers of developing fourth-stage larvae (length > 1,6 50 mum) in April (2.6%), June (7.4%), September (11.3%), and November (3.7%), worms were early fourth-stage larvae (EL4) or fully developed adults. Overall, the proportion of EL4 in individual deer ranged from 19 to 97%; in male (n = 3) and female (n = 15) deer the proportions of EL4 were 22.5% and 67%, respectively. The mean proportions of EL4 in female deer were 51.4% (April), 63.2% (June), 78.1% (September), and 7 4.7% (November), but there was no difference (P > 0.05) among the 4 mo nths. In spite of the absence of a significant difference between mont hs in proportions of EL4, we propose that the larger absolute numbers of EL4 in June and September was due to a seasonal arrested developmen t that occurred among stomach worms of white-tailed deer. Further, bas ed on the presence of higher numbers of EL4 and adults compared to dev eloping fourth-stage larvae at all collections, we believe that arrest ed development is an integral part of the life cycle of these nematode s.