2 Trap In Tamil Pdf Download
Thi Sandland
Limited success has been achieved using traditional vector control methods to prevent the transmission of dengue viruses. Integrated control programs incorporating alternative tools, such as gravid ovitraps (lethal ovitraps and sticky ovitraps) may provide greater potential for monitoring and reducing vector populations and dengue virus transmission. We had developed an autocidal gravid ovitrap (AGO) as a simple, low-cost device for surveillance and control of Ae. aegypti without the use of pesticides that does not require servicing for an extended period of time. The purpose of our study was to improve the efficacy and efficiency of this device.
Competitive assays were performed in the laboratory and an outdoor cage to evaluate whether modifications to the structure and appearance of our original trap design (AGO-A), and the addition of an olfactory bait (hay infusion), improve trap function. The performance of a modified trap design (AGO-B) was then assessed and compared with conventional ovitraps in a series of field tests in San Juan City, Puerto Rico. Generalized linear mixed models were used to analyze adult Ae. aegypti capture data from the laboratory, outdoor cage and field experiments.
Trap designs and infusion baits were compared in competitive assays under semi-natural conditions in two field cages. Most of these experiments were performed in Cage A, a 10 m diameter, 3.4 m high geodesic dome tent (Shelter Systems, Santa Cruz, California, USA), with two 0.2 1.5 m and four 1.5 1.5 m screen windows providing ventilation. Traps were arranged at fixed locations in a ring 1.6 m from the wall of the field cage, with a minimum distance of 2.6 m (6 or 8 traps) or 4.8 m (3 or 4 traps) between traps. A single experiment (attraction to anaerobically fermented hay infusion in the AGO-B; see below) was conducted in a smaller, rectangular field enclosure (Cage B; 7.0 2.7 3.7 m) with screen walls on two adjacent sides. In Cage B, a trap was assigned to each of two locations approximately 2 m apart in the center of the enclosure.
In each trial, 120 (Cage B) or 150 (Cage A) gravid Ae. aegypti females were released from the center of the arena. Experiments were conducted from 2.5 hrs prior to sunset, and traps were recovered 2.5 hrs after sunrise, corresponding to the diel rhythm of oviposition activity of gravid Ae. aegypti females [37]. A sweep net and BG-sentinel trap (operated for 6 hours) were used to collect females remaining in the cage after each trial.
Data from the competitive assays in the screened room and field cage were analyzed by generalized linear mixed models (GLMMs) with repeated measures (SPSS ver. 12.0, SPSS, Inc., Chicago, Illinois, USA), with number of females captured as the response variable, treatment as a fixed effect, and trap location (subject) and trial (repeated measure) as random effects. Results are reported as marginal means with 95 percent confidence intervals. Bonferroni adjustments were made for assays comparing more than two treatments.
The original autocidal gravid ovitrap (AGO-A). Components include a 19 l black pail (a), a white pail lid (b), an 8.8 cm entrance diameter (c) a white capture surface (CS) coated with adhesive (d), PAM (e), a 2.5 l capacity infusion reservoir (f), and a screen barrier between the CS and the infusion reservoir (g).
The improved autocidal gravid ovitrap (AGO-B). Components include a 19 l black pail (a), a black pail lid (b), a 12.8 cm entrance diameter (c), a black capture surface (CS) coated with adhesive (d), PAM (e), a 9.3 l capacity infusion reservoir (f), and a screen barrier between the CS and the infusion reservoir (g). A conventional ovitrap is visible in the foreground of the photograph, on the right-hand side of the AGO-B.
In the first field experiment, numbers of adult mosquitoes captured in the original trap model (AGO-A) and the improved device (AGO-B) were compared from 15 February to 18 April. Traps, constructed as described previously, were baited with a 30 g hay packet (in situ infusion) and distributed among the 30 selected properties. One property was later excluded from the experiment after home renovations prevented access to the traps.
In the third field experiment (6 June to 21 July), we examined the relative contribution of the in situ infusion to trap performance during extended use (> 6 weeks) by comparing adult captures in traps baited with a hay packet (AGO-B) and traps without a hay packet (only water; AGO-Bw). Samples were collected from AGOs at all 30 selected properties in this experiment.
At the conclusion of field experiment 1 (62 days), we conducted a census of the condition of AGO-Bs, and the volume of infusion remaining in each trap was measured. It was observed that the CS of the AGO-B becomes coated with many small flies, dust and other debris after extended use. Used CSs from twelve randomly selected AGO-Bs were brought back to the laboratory to test whether their ability to capture gravid females had diminished after extended use.
In both trap designs (AGO-A, AGO-B), a 1:1 dilution of AF infusion bait resulted in a significantly greater number of females captured under semi-natural conditions (Table 1). Fermentation conditions of the infusion bait had a significant influence on attraction to the AGO-B (Table 2); greater numbers of females were captured in traps baited with an infusion aged in a closed container (anaerobic), compared with traps where the infusion was aged in situ. Neither the mass of hay used to produce infusion in situ, nor the presence of conspecific larvae in the hay infusion significantly influenced attraction to the AGO-B in the field cage (Table 2).
In the first field experiment, the mean numbers of Ae. aegypti females collected on each collection date were on average 3.7 fold greater in the AGO-B than in the original (AGO-A) trap design (Figure 4). In the second field experiment (Figure 5), traps with a partial replacement of the infusion bait (AGO-Bp), and traps with a complete bait replacement (AGO-B) captured similar numbers of Ae. aegypti females on most collection dates. In the third field experiment (Figure 6), the addition of hay increased the capture rate of Ae. aegypti females in the AGO-B by an average of 1.6 fold, compared with traps only baited with water (AGO-Bw).
Field comparison of original (AGO-A) and improved (AGO-B) trap designs. Cumulative daily rainfall and average daily mean air temperature 8 to 28 days preceding sampling (a), and the average numbers of Aedes eggs collected in ovitrap pairs and Aedes aegypti adult females collected in AGOs (b), from 15 February to 18 April, 2011 (Field experiment 1).
Field comparison of the improved trap with full (AGO-B) or partial (AGO-Bp) infusion bait replacement. Cumulative daily rainfall and average daily mean air temperature 8 to 28 days preceding sampling (a), and the average numbers of Aedes eggs collected in ovitrap pairs and Aedes aegypti adult females collected in AGOs (b), from 18 April to 12 May, 2011 (Field experiment 2).
Field comparison of the improved trap baited with infusion (AGO-B) or water (AGO-Bw). Cumulative daily rainfall and average daily mean air temperature 8 to 28 days preceding sampling (a), and the average numbers of Aedes eggs collected in ovitrap pairs and Aedes aegypti adult females collected in AGOs (b), from 6 June to 21 July, 2011 (Field experiment 3).
Over the course of field testing, increases in the average capture rate and the frequency of positive samples were observed in the paired ovitraps and AGO devices, coincident with increasing rainfall intensity in each sequential experiment (Table 3, Figures 4, 5 and 6). In field experiment 1, when Ae. aegypti abundance and rainfall were lowest, the AGO-B had a lower coefficient of variation and higher proportion of positive samples than either the AGO-A or the ovitrap pair (Table 3). Differences in sensitivity or precision between the AGO-B and other sampling devices were lower or absent in the second and third experiments. Average capture rates of adult females in AGOs were significantly correlated with cumulative rainfall preceding sampling in field experiments 1 and 2, but this relationship was marginally insignificant in the third experiment (Table 3). No significant correlations were detected between lagged rainfall and collections in the paired ovitraps (Table 3). For all three field tests, both trap design and cumulative rainfall 2 to 4 weeks prior to sampling were significant sources of variability in adult female Ae. aegypti collections in the AGO (Table 4). Average daily air temperature 2 to 4 weeks prior to sampling also was a significant covariate in the models for field experiments 2 and 3 (Table 4).
Our objective in this study was to improve our original autocidal gravid ovitrap device so that it was a more efficacious and practical tool for vector surveillance and control. Several trap designs intermediate to the AGO-A and AGO-B were compared in order to assess sequential changes to the appearance, the trap entrance, and volume/surface area of the attractant. We also assessed the contribution of a hay infusion bait to trap performance.
Attraction of gravid Ae. aegypti females to plant-based infusions is influenced by the type and concentration of organic material used, and the length of time and conditions under which the infusion is aged [48, 49]. Ponnusamy et al.[50] demonstrated that these factors influence the diversity and abundance of microorganisms associated with attraction. In ovitrap devices, the addition of plant material as a substrate for microbial growth (ie., in situ infusion) can extend the duration of olfactory attraction between replacement of the infusion bait [32]. However, as the organic material is consumed, the attractiveness of the infusion odor may diminish due to biochemical changes in the infusion resulting from succession in the microbial community. Variability in relative attractiveness over time could limit the precision of surveillance data collected using infusion-baited ovitraps. In our third field experiment, the relative difference between captures in water baited and infusion baited AGO-Bs was consistent over time, suggesting that the attractiveness of the in situ infusion to gravid Ae. aegypti females was not diminished after more than 6 weeks of use. This would indicate that changes in infusion odor are unlikely to introduce a strong bias in surveillance data collected with the AGO-B during long-term use.
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