Spatial signature of aphids, coccinellids and carabids in alfalfa fields
عنوان دوره: دومین کنگره بین المللی حشره شناسی ایران
نویسندگان
چکیده
Alfalfa, Medicago sativa L. is an important forage crop with a considerable effect on quality of dairy products. Alfalfa fields are suitable habitats for a large number of pests and beneficial insects. Aphids feeding on alfalfa stunts plant growth and reduces yield. Predators such as coccinellids and ground beetles can play an important role in control of aphids and other pests in alfalfa fields. In this study, spatial signature of aphids, coccinellids and ground beetles was determined using geostatistics.
This study was conducted in 2016 within three alfalfa fields (2, 1.8 and1.4 ha), located in the experimental farm of Faculty of Agriculture, University of Tabriz. No insecticide was applied in the fields during the study. All fields were divided into 20 × 20 m grids. Sampling was started when plants height reached 10 cm, and continued until cutting the hay. Pitfall traps were used for sampling carabids (one trap per grid). The traps contained 250 ml water and 250 ml ethylene glycol. Carabids captured by pitfall traps, were collected every two weeks and transferred to the laboratory. Coccinellids were sampled using a 1 × 1 m quadrat. Two quadrats were thrown at each grid randomly, and all life stages of coccinellids were counted and recorded weekly. In order to sample aphids, 10 stems were cut randomly from each grid and shaken into a white pan. All aphids fallen in the pan were counted and recorded. The collected data were analyzed using geostatistics and spatial correlations were determined. The degree of spatial dependence was measured using k index, defined as the ratio between the nugget and sill values of the variogram. Values below 0.8 indicate that the distribution is aggregated. Spatial distribution maps were generated using ArcGIS 9.3 software.
Results of geostatistical analysis indicated that aphids including Therioaphis maculata (Buckten) and Acyrthosiphon pisum (Haris) had aggregated distribution in the alfalfa fields and values of k were below 0.8 in 28 out of 40 datasets. Coccinellids showed random distribution because k was greater than 0.8 in 41 out of 77 datasets. Results also indicated that ground beetles had almost aggregative distribution and k was below 0.8 in 6 out of 9 datasets.
Determining spatial signature of aphids and natural enemies provides useful information about their ecology and relationships. This information can be used in biological control and site- specifically management of pests.
This study was conducted in 2016 within three alfalfa fields (2, 1.8 and1.4 ha), located in the experimental farm of Faculty of Agriculture, University of Tabriz. No insecticide was applied in the fields during the study. All fields were divided into 20 × 20 m grids. Sampling was started when plants height reached 10 cm, and continued until cutting the hay. Pitfall traps were used for sampling carabids (one trap per grid). The traps contained 250 ml water and 250 ml ethylene glycol. Carabids captured by pitfall traps, were collected every two weeks and transferred to the laboratory. Coccinellids were sampled using a 1 × 1 m quadrat. Two quadrats were thrown at each grid randomly, and all life stages of coccinellids were counted and recorded weekly. In order to sample aphids, 10 stems were cut randomly from each grid and shaken into a white pan. All aphids fallen in the pan were counted and recorded. The collected data were analyzed using geostatistics and spatial correlations were determined. The degree of spatial dependence was measured using k index, defined as the ratio between the nugget and sill values of the variogram. Values below 0.8 indicate that the distribution is aggregated. Spatial distribution maps were generated using ArcGIS 9.3 software.
Results of geostatistical analysis indicated that aphids including Therioaphis maculata (Buckten) and Acyrthosiphon pisum (Haris) had aggregated distribution in the alfalfa fields and values of k were below 0.8 in 28 out of 40 datasets. Coccinellids showed random distribution because k was greater than 0.8 in 41 out of 77 datasets. Results also indicated that ground beetles had almost aggregative distribution and k was below 0.8 in 6 out of 9 datasets.
Determining spatial signature of aphids and natural enemies provides useful information about their ecology and relationships. This information can be used in biological control and site- specifically management of pests.
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