Abstract
Determining the spatio-temporal distribution and association of pests and natural enemies would be useful for implementing biological control of pests and could also be used in site-specific pest management. In this study, the spatio-temporal distribution and association of aphids, plant bugs, and natural enemies were assessed in alfalfa fields using geo-statistics and spatial analysis by distance indices (SADIE). Additionally, the effect of alfalfa hay-harvesting on the spatial and temporal distribution of these insects was investigated for the first time. Geostatistical analysis indicated that the degree of dependence (DD) was ≥75% for 11 out of 39, 9 out of 35, 3 out of 12, 10 out of 29, and 2 out of 20 datasets for pea aphid Acyrthosiphon pisum, spotted alfalfa aphid Therioaphis maculata, cowpea aphid Aphis craccivora, alfalfa plant bug Adelphocoris lineolatus, and tarnished plant bug Lygus rugulipennis, respectively. The results also indicated that DD was ≥75% in 7 out of 45, 18 out of 45, and 3 out of 20 datasets for Coccinella septempunctata, Hippodamia variegata, and Pterostichus melanarius, respectively. Harvesting decreased the aggregation of the ladybirds, which resulted in a decrease in the index of aggregation. The geo-statistics results were confirmed by SADIE in 75% of datasets. These results can be used in biological control and site-specific management of aphids and plant bugs in alfalfa fields.
Highlights
Alfalfa Medicago sativa L., is one of the earliest plants to be domesticated by humans and plays an important role in the quality of dairy products
The spatio-temporal distribution and association of aphids, plant bugs, and natural enemies were determined in alfalfa fields using geo-statistics and spatial analysis by distance indices (SADIE)
SADIE results agreed with the results of geo-statistics in 75% of the datasets, which highlights a good match level
Summary
Alfalfa Medicago sativa L., is one of the earliest plants to be domesticated by humans and plays an important role in the quality of dairy products. Alfalfa fields typically have a rich insect fauna and they are suitable habitats for a large number of pests and beneficial insects. Different species of aphids are important pests in alfalfa fields in Iran. Aphid damage starts at the end of March and continues through the spring. Severe aphid infestation stunts plant growth and reduces yield and may even kill alfalfa plants. Aphids produce large amounts of honeydew and make the alfalfa plants sticky, which causes problems during harvest [2,3]. Aphid populations are controlled by natural enemies in alfalfa fields and, usually, no specific chemical is applied to control them, unless the population is very high
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