Individual study: Population fluctuations of selected arthropods in alfalfa: influence of two harvesting practices
Summers C.G. (1976) Population fluctuations of selected arthropods in alfalfa: influence of two harvesting practices. Environmental Entomology, 5, 103-110
This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.
Leave part of the crop or pasture unharvested or uncut
A controlled study in 1972 of two 16.1 ha alfalfa Medicago sativa fields in California, USA (Summers 1976) found that predator and pest numbers were higher in the field with uncut strips than the completely cut field. There were 18,044 individual predators and 16,138 pest (lygus bugs Lygus spp. and pea aphids Acyrthosiphon pisum) individuals in the field with uncut strips and 7,131 predators and 12,557 pests in the completely cut field. Predators included spiders (Araneae), damsel bugs Nabis spp., green lacewing Chrysoperla (Chrysopa) carnea and ladybirds (Coccinellidae). Lygus bugs moved from uncut strips into cut areas, but moved back to uncut strips when cutting occurred. Predatory species showed a similar pattern. Alfalfa hay protein content was slightly higher in the field with uncut strips (18.1-20.7% protein) than the completely cut field (17.1-18.2%) but modified crude protein was slightly lower. One field had banks 1 m-wide and 0.2 m high distributed every 15-25 m. At each mowing period, banks were cut alternately (one alfalfa strip left uncut at every alternate raised strip, the next bank cut). Cuttings were distributed either side of the strip. Invertebrates were sampled on uncut and cut strips and between strips (10 samples/location) using a D-vac suction sampler. The second field was cut completely, and sampled using the same method as in the field with cut strips. Sampling took place one week after strip-cutting began (after the second cut, 7th May) and continued bimonthly until mid-September.