Effects of different intensities of artificial light at night on multi-trophic population dynamics

Randomized block design (6 blocks) with different intensities of artificial light at night as treatment (control, 0.1,1,5,10,20,50,100 lux). Each treatment replicated six times with a total of 48 mesocosms (Cage). Each mesocosm contained experimental plant-insect communities which consisted of two plant species: broad bean (Vicia faba, L., var. the Sutton) and barley (Hordeum vulgare L.), with bean plants as a resource for three aphid species: (1) the black bean aphid Aphis fabae (Scopoli), (2) the pea aphid Acyrthosiphon pisum (Harris), and (3) the vetch aphid Megoura viciae (Buckton). For each aphid species recorded the number of winged (w) and unwinged morphs. Each of the aphid species was attacked by a specialist parasitoid, these being Lysiphlebus fabarum (Marshall), Aphidius ervi (Haliday), and Aphidius megourae (Stary), respectively. Barley plants were a resource for the grain aphid Sitobion avenae (Fabricius). These separate communities were linked by the generalist parasitoid Praon dorsale (Haliday), which attacked the aphids Sitobion avenae (P.dor.s), Acyrthosiphon pisum (P.dor.a), and Megoura viciae (P.dor.m). From week 1 until the termination of the experiment after 9 weeks, all species on all or half of the plants were counted on a weekly basis. Plantbiomass (in g dry weight) was measured at the end of the experiment, after cutting, washing and drying the plants (for 48h at 50 degrees Celisus) from 1 pot per mesocosm. However there are missing data points for this plant biomass dataset, due to the loss of labels. For measuring the impact of different intensities of artificial light at night (0, 0.1,5,20,100 lux) on plants without aphids another experiment was set up. Each treatment replicated six times with a total of 30 mesocosms (Cage). Each mesocosm contained a pot with 4 2-week-old broad beans (Vicia faba, L., var. the Sutton). Plantbiomass (in g dry weight) was measured at the end of the experiment after 3 weeks, after cutting, washing and drying the plants (for 48h at 50 degrees Celisus).

Third instar M. viciae aphid individuals were set onto 2 week old plants at densities varying from 5 to 200, with each plant placed in a 47.5 x 47.5 x 47.5 cm Bug Dorm cage. One female Aphidius megourae parasitoid was placed in each cage for a 24-hour period, after which point it was removed. Aphids were then left for 2 weeks before all mummies were counted. We used two set ups: unlit controls and artificial light at night at 20 lux and control, 1 lux and 20 lux. After two weeks all mummified aphids were counted. To test for the behavioural response of parasitoids to different light intensities, 100 3rd instar M. viciae aphids were placed on a 3 week old broad bean. This infested plant was then placed in a cage in complete darkness. Different light treatments were then applied over the top of the cage, these being 0 (control) 1, 5, 20, and 100 lux, measureable at the height of the plant. 20 mated female A. megourae parasitoids were then released into the cage, and were left for one hour. After one hour the locations of the parasitoids (on the or away from plant) were noted. To test for parasitoid attack rate during day and night, single broad bean plants with 60 3rd star M. viciae aphids per plant, and placed in a cage. These aphids were left to settle for 1 day before being placed in incubators (Percival Model 1-30 vl) set to 18 degrees Celsius with a 12:12 day night cycle. A single, mated female A. megourae parasitoid was placed in each cage, and left for 12 hours in either dark or light settings. After 12 hours the parasitoid was removed and placed in another cage, again with 60 3rd instar aphids and left for a further 12 hours at the opposite light treatment.