Parous rate and longevity of anophelines mosquitoes in bure district, northwestern Ethiopia

The intensity of malaria transmission is measured by parous rate, daily survival rate, human blood meal frequency, sporozoite rate, and entomological inoculation rates. Female parous status is a key index of vector competence, adult vector longevity, recruitment rate of adult, and the length of a gonotrophic cycle. Hence, the present study was aimed to investigate the parous rate and the longevity of Anopheles mosquitoes in Bure District, Northwestern Ethiopia. Parous rate was estimated as the number of mosquitoes with parous ovaries divided by the number of females dissected multiplied by 100. Mosquito life expectancy (longevity as d) was estimated by. One way- ANOVA was applied to confirm the presence of parous rate difference in the villages (p < 0.05). A total of 952 unfed hosts-seeking Anopheles mosquitoes was dissected for parous rate determination. The overall parous rate of An. arabiensis in the district was 52.0%, and the highest parous rate was recorded in Shnebekuma than other villages (F 2, 33 = 6.974; p = 0.003). Similarly, the parous rate of An. cinereus showed significant variation among villages (F 2, 33 = 5.044, p = 0.012) and the highest rate (63.0%) was recorded in Bukta. The mean longevity of An. funestus, An. arabiensis, An. coustani, An. squamosus, An. pharoensis, and An. cinereus was 6.5 days, 4.6 days, 3.5 days, 3.7 days, 2.7 days, and 2.2 days, respectively. The longevity of each species was not sufficient to complete the life cycle of malaria parasite for malaria transmission throughout the year because P. falciparum requires from 12–14 day.

Bloodmeal sources and feeding behavior of anopheline mosquitoes in Bure district, northwestern Ethiopia

BACKGROUND

Mosquito bloodmeal sources determine the feeding rates, adult survival, fecundity, hatching rates, and developmental times. Only the female Anopheles mosquito takes bloodmeals from humans, birds, mammals, and other vertebrates for egg development. Studies of the host preference patterns in blood-feeding anopheline mosquitoes are crucial to determine malaria vectors. However, the human blood index, foraging ratio, and host preference index of anopheline mosquitoes are not known so far in Bure district, Ethiopia.

METHODS

The origins of bloodmeals from all freshly fed and a few half-gravid exophagic and endophagic females collected using Centers for Disease Control and Prevention light traps were identified as human and bovine using enzyme-linked immunosorbent assay. The human blood index, forage ratio, and host feeding index were calculated.

RESULTS

A total of 617 specimens belonging to An. arabiensis (n = 209), An. funestus (n = 217), An. coustani (n = 123), An. squamosus (n = 54), and An. cinereus (n = 14) were only analyzed using blood ELISA. Five hundred seventy-five of the specimens were positive for blood antigens of the host bloods. All anopheline mosquitoes assayed for a bloodmeal source had mixed- rather than single-source bloodmeals. The FR for humans was slightly > 1.0 compared to bovines for all Anopheles species. HFI for each pair of vertebrate hosts revealed that humans were the slightly preferred bloodmeal source compared to bovines for all species (except An. squamosus), but there was no marked host selection.

CONCLUSIONS

All anopheline mosquitoes assayed for bloodmeal ELISA had mixed feeds, which tends to diminish the density of gametocytes in the mosquito stomach, thereby reducing the chance of fertilization of the female gamete and reducing the chances of a malaria vector becoming infected. Moreover, An. coustani was the only species that had only human bloodmeals, meaning that this species has the potential to transmit the disease. Therefore, combination zooprophylaxis should be reinforced as a means of vector control because the study sites are mixed dwellings.

Species diversity and distribution of Anopheles mosquitoes in Bure district, Northwestern Ethiopia

Malaria is one the leading health problem of the Ethiopia. Previously, areas above 2,000 m elevation were considered as malaria free areas. However, the major malaria epidemics were seen in areas at an altitude up to 3,000 m above sea level. These epidemics were due to climate and land-use changes (ecological changes) and still malaria is a growing health problem in highland parts of Ethiopia. This study aimed to investigate the species diversity, abundance and distribution of Anopheles mosquitoes in highland fringe of Bure district, Northwestern Ethiopia. It was done in the three different agroecological villages, Bukta (Irrigated), Workimdr (non-irrigated with few dry season breeding habitats) and Shnebekuma (non-irrigated with many dry season breeding habitats). Anopheles mosquitoes were collected by the Centers for Disease Control and Prevention Light Traps Catches, Pyrethrum Spray Catches, and Artificial Pit Shelters (APSs) from twenty-seven houses, thirty houses, and six APSs, respectively. Anopheles mosquitoes were identified morphologically to species using standard keys. Furthermore, molecular identification of Anopheles gambiae s.l was carried out using species-specific Polymerase Chain Reaction. Independent T-Test and One-way- ANOVA were employed to compare the mean mosquito's density between villages and species, indoor and outdoor host seeking mosquitoes. Descriptive statistic was used to calculate the proportion of each Anopheles species. Nine Anopheles mosquito species were identified in the study area which includes: Anopheles demeilloni, An. arabiensis, An. funestus group, An. coustani, An. squamosus, An. cinereus, An. pharoensis, An. rupicolus, and An. natalensis. Of the 4,703 Anopheles mosquitoes collected, An. demeilloni was the most prominent (50.7%, n = 2383) whereas An. rupicolus (0.03%, n = 3), and An. natalensis (0.02%, n = 1) were the least abundant. Higher mean density of Anopheles mosquitoes was collected from the non-irrigated village (2.395 ± 0.100) than irrigated (1.351 ± 0.109) (p = 0.001). In conclusion, three of the most important malaria vectors (An. arabiensis, An. funestus group and An. pharoensis) of Ethiopia were recorded in the study sites, especially the first two was found thought-out the year. Most of the Anopheles mosquitoes were collected from non-irrigated villages. Thus, breeding habitat management must be practiced throughout the year together with long-lasting insecticide-treated nets and insecticide residual sprays.

Distribution and extent of Cotesia Flavipes Cameron (Hymenoptera: Braconidae) Parasitism in Northeastern Ethiopia

The distribution and extent of parasitism of Cotesia flavipes Cameron (Hymenoptera: Braconidae) on stem borer species attacking maize and sorghum were assessed in three zones of northeastern Ethiopia. Cotesia flavipes was found to be the key larval parasitoid of cereal stem borer species in all areas surveyed. This parasitoid has been introduced into several African countries for the control of Chilo partellus in maize and sorghum, but it has never been released in Ethiopia. The survey results indicated that the distribution and extent of parasitism of Cot. flavipes followed the distribution and severity of its suitable host, C. partellus. A Cotesia flavipes parasitism rate of between 33% and 82% was recorded in sub-moist warm (lowland) AEZs of all zones. In contrast, a parasitism rate of less than 6% was recorded in moist, cool highland areas where Busseola fusca was the predominant species. Cotesia flavipes caused lower rate of parasitism on stem borers in maize (up to 72%) than that of sorghum (up to 82%) in the three zones. In summary, high rates of parasitism of Cot. flavipes were recorded in lowland areas where C. partellus was the dominant borer species and low rates of parasitism were recorded in highland areas where B. fusca was the predominant species. Cotesia flavipes caused the highest parasitism (82%) on C. partellus. This result verified that Cot. flavipes contributed to the reduction of C. partellus population in lowlands, regardless of the zone, and its rate of parasitism varied between crop stages, crop types, elevations, host, and host stages. Findings of this study have particularly relevant information on the contribution of Cot. flavipes to the population reduction of stem borers, time or stage of its occurrence in relation to host stages and crop stages, and its distribution in relation to the availability of a suitable host across each zone. In conclusion, this larval parasitoid plays an important role in reducing stem borer populations and can be used as one component of integrated stem borer management in northeastern Ethiopia.

Effect of temperature and relative humidity on the development and fecundity of Chilo partellus (Swinhoe) (Lepidoptera: Crambidae)

The spotted stemborer, Chilo partellus (Swinhoe) (Lepidoptera: Crambidae), is one of the most important insect pests attacking maize and sorghum in Ethiopia. Recent studies have indicated that the pest is spreading to new locations where it was not reported before. In the current study, laboratory investigations were carried out to determine the combined effect of different levels of relative humidity and temperature regimes on the development and fecundity of C. partellus, as these physical factors are known to play an important role in the life cycle of insects and adaptability to local climate. Developmental time, longevity, potential fecundity and realized fecundity of C. partellus were measured under controlled conditions. Three temperature regimes (22°C, 26°C and 30°C) and three relative humidity levels (40%, 60% and 80%) were tested. It was found that temperature, relative humidity (RH) and their interaction significantly affected the developmental time, adult longevity, potential fecundity and realized fecundity of the pest. Developmental time was inversely related to temperature. Mean duration of C. partellus life cycle was 70.2 days at 22°C and 80% RH, whereas it took only 26.5 days to complete its life cycle at 30°C and 40% RH. Male and female longevity were similar in most cases. The adult life span ranged between 6.9-11.1 days at 22°C and 3.1-7.2 days at 30°C for different levels of relative humidity. The most suitable conditions for C. partellus development and fecundity were 26-30°C temperatures regimes and 60-80% RH levels.

Biology of barley shoot fly Delia flavibasis Stein (Diptera: Anthomyiidae) on resistant and susceptible barley cultivars

The biology of barley shoot fly Delia flavibasis was studied using resistant (Dinsho and Harbu) and susceptible (Holker) barley cultivars at Sinana Agricultural Research Center, Ethiopia. A higher number of eggs was laid on Holker (17 eggs/female) than on Dinsho (11 eggs/female) or Harbu (12 eggs/female). However, there were no differences between cultivars in preoviposition and total reproductive periods. The shortest time required to complete larval, pupal and total developmental stages from egg to adult emergence occurred when the insect was reared on the cultivar Holker. Pupal weight, adult emergence and adult longevity did not differ between cultivars. The female to male sex ratio was 1:1. This study enabled us to understand the duration of each of the life stages of D.flavibasis, which will undoubtedly aid researchers and growers to design a sustainable management strategy against barley shoot fly.

Evaluation on potential of wild hosts as trap plants for managing gramineous stemborers in maize based-agroecosystem

As part of habitat management system to control cereal stemborers, various wild hosts used as trap plants were studied during the dry season from November 2003 to March 2004 at Melkassa, central Ethiopia. Five wild hosts of the family Poaceae [Pennisetum purpurum (Schumach), Sorghum vulgare variety sudanense (Pers.), Panicum coloratum L., Sorghum arundinaceum Stapf, and Hyperrhania rufa (Nees)] were evaluated as trap plants in maize, Zea mays L.,-based agroecosystem. The results of the study showed that maize plots surrounded by all tested wild hosts had significantly lower mean percentage of foliage damage and stemborer density than maize monocrop plots 15 m away from the treatment blocks. Interestingly, mean foliar damage and stemborer density between maize plots surrounded by wild hosts and maize monocrop plots within the treatment blocks was not significant. Percentage of tunneled stalks was significantly greater in maize monocrop plots 15 m away from the treatment blocks than in maize plots surrounded by all tested wild host plant species. Moreover, the highest mean percentage of parasitism (62%) of Chilo partellus (Swinhoe) by Cotesia flavipes (Cameron) was recorded in maize plots surrounded by P. purpureum. Therefore, the findings revealed that these wild hosts have considerable merit to be used as trap plants in the development of strategies for managing cereal stemborers in maize crops.

Evidence of the establishment of Cotesia flavipes (Hymenoptera: Braconidae), a parasitoid of cereal stemborers, and its host range expansion in Ethiopia

Three lepidopteran cereal stemborers, Chilo partellus (Swinhoe) (Crambidae), Busseola fusca Fuller, and Sesamia calamistis Hampson (Noctuidae) were collected from maize and sorghum in Ethiopia. The noctuid stemborers are indigenous to Africa while C. partellus is an introduced species from Asia. In 1999, the Asian stemborer parasitoid, Cotesia flavipes Cameron (Braconidae) was found to be widespread in Ethiopia, even though it had never been released in the country. In addition to attacking Chilo partellus, Cotesia flavipes was reared from B. fusca and S. calamistis. The origin of C. flavipes in Ethiopia may have been Somalia where it was released in 1997 near the border with eastern Ethiopia. Percent parasitism of borers by C. flavipes was higher in eastern Ethiopia than other surveyed regions, and parasitism was higher in 2000 than 1999. Parasitism was higher when cereals were intercropped with other plants and when wild grass hosts of stemborers were present.