Bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV) are arthropod-transmitted viruses in the genus Orbivirus of the family Reoviridae. These viruses infect a variety of domestic and wild ruminant hosts, although the susceptibility to clinical disease associated with BTV or EHDV infection varies greatly among host species, as well as between individuals of the same species. Since their initial detection in North America during the 1950s, these viruses have circulated in endemic and epidemic patterns, with occasional incursions to more northern latitudes. In recent years, changes in the pattern of BTV and EHDV infection and disease have forced the scientific community to revisit some fundamental areas related to the epidemiology of these diseases, specifically in relation to virus-vector-host interactions and environmental factors that have potentially enabled the observed changes. The aim of this review is to identify research and surveillance gaps that obscure our understanding of BT and EHD in North America.
Relationships between temperature and life history parameters were determined for the stable fly, Stomoxys calcitrans (L.). Median immature developmental times ranged from > 60 d at 15 degrees C to < 12 d at 30 degrees C, with minimum time at 30.6 degrees C. Egg survival decreased from 0.98 at 15 degrees C to 0.91 at 20 degrees C, then increased to 0.98 at 35 degrees C. Larval survival ranged from 0.83 at 20 degrees C to 0.65 at 35 degrees C, and pupal survival ranged from 0.93 at 20 degrees C to 0.42 at 35 degrees C with maxima at 22.1 degrees C and 19.9 degrees C for larvae and pupae, respectively. Median longevity of females and males were greatest at 17.3 degrees C. Time to 50% survival ranged from > 30 d at 15 degrees C to < 6 d at 35 degrees C. Daily fecundity averaged 1.07, 8.89, 14.88, 26.22, and 7.90 eggs per female per day at 15, 20, 25, 30, and 35 degrees C, respectively. Lifetime fecundity ranged from < 30 eggs per female at 15 and 35 degrees C to > 700 eggs per female at 25 degrees C and was greatest at 25.3 degrees C. Net reproductive rate, and the intrinsic rate of increase had maxima at 25.3 and 27.8 degrees C, and mean generation time was minimum at 33.4 degrees C. Proportional variation in the time of immature development and adult longevity were independent of temperature, but proportional variation in the time of oviposition was related inversely to temperature. Extreme temperatures appeared to lengthen the preoviposition period and reduce the duration of egg production. Relationships were compared with previous studies. Equations developed and presented in this article will be used to develop a temperature-dependent stable fly population model.
Seasonal abundance of stable flies and house flies was studied at four dairies in southern Alberta, Canada, from May to October in 1989, 1990, and 1991. Stable flies were active from May to October in all years and showed population peaks in August and September. The weekly rate of change of stable fly populations was influenced by temperature and accumulated degree-days above 10 degrees C. The weekly rate of change of stable fly populations showed four peaks which were attributed to the emergence of an initial generation which had overwintered, followed by an additional three generations. Stable fly attacks on dairy cows occurred mainly from July through October, corresponding with the last two generations. House fly population abundance was much lower than stable fly populations and showed peaks in June, July, and September. Weekly changes in house fly abundance were not influenced by temperature and only weakly influenced by accumulated degree-days above 10 degrees C. Peaks in the weekly rate of change were associated with emergence of an initial, overwintering generation followed by four generations produced throughout the summer.
(1174), or with grass srlage (X2637). Concentrations of water-soluble carbohydrates were higher (P < 0.05) in inoiulated than in control silages. Although inoculants appeared to increase the numbers of lactit acid producing bacteria (LAB) at ensiling, post-ensiling numbets (cfu g-1) of yeasts and molds.were lower (P < 0'05) in inoculated than in control silages. Lactic acid concentrations and pH were similar arnong the silages and variations in the growth of yeast and mold populations-could not be explained by differences in the production of volatile fatty acids (VFA) among silages.Inoculation of barlly silage with either inoculanr increased (P < 0.01) the average daity gain of lambs. A digestibilrty expelT:lt with 12 growing ram lambs showed that inoculants did not alter (P > 0.05) DM intzike, feed efficiency or the digestion of DM' organic iatter, icid detergent fiber (ADF) and neutral derergent fiber (NDF). Nitrogerr intake and retention were greater (P < 0'05) inlambs fed silage inoculated wrth ll74 as compared withiontrol silage. Yeast populations were increased (P < 0.05) in control and ll7 4 after 2-dof exposure to air but it requirid 13 d for a similar yeast population to be established inX2637 silage. Increases in the mold populations within the silages were noted after 2, 5 and 13 d of exposure to air for control' 117 4 and X2637 ' respectively. Theiemperature of control silage increased (P < 0.05) 2 dafter exposure to air, whereas increases in temperature were delayed for 4 d in lli4 and g d in X26i7. Temperatures rose as high as 30'C in control silage, but did not exceed24"C in inoculated silages during the 13 d period.
The growth and survival of Stomoxys calcitrans (L.) larvae on egg yolk medium inoculated with bacteria isolated from a colony of stable flies was evaluated. Five species of bacteria--Acinetobacter sp., Aeromonas sp., Empedobacter breve (Holmes & Owen), Flavobacterium odoratum Stutzer, and Serratia marcescens Bizio--were identified according to fatty acid profiles using a microbial identification system. Larvae failed to develop on uninoculated plates, confirming that bacteria are required to complete development. Larvae also failed to complete development on plates inoculated with Aeromonas sp. and S. marcescens, and died during the 1st instar. Larvae completed development on the remaining 3 bacterial species as well as on Escherichia coli (Migula). Survival was generally higher when larvae were reared on Acinetobacter sp. and F. odoratum compared with E. coli and E. breve. Egg density did not influence larval survival, although the variability in survival was lowest using 20 and 40 eggs per plate. Larval survival in mixed cultures of Acinetobacter and Flavobacterium averaged 22.7% lower than survival in the pure cultures, and averaged 21.6% higher in mixed cultures of Empedobacter and Flavobacterium compared with pure cultures. Larval survival in mixed cultures did not differ significantly from mean survival in pure cultures for combinations of Acinetobacter and E. coli, Acinetobacter and Empedobacter, E. coli and Empedobacter, and E. coli and Flavobacterium. Larval developmental time was faster on all mixed bacterial cultures compared with developmental time on pure bacterial cultures. Optimal sample sizes and egg numbers are presented for detecting specified differences in larval survival. This rearing procedure will be useful for studying insect-microbe interactions and evaluating mortality using bacterial agents.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.