Movement between crops and weeds: temporal refuges for aphidophagous insects in Central Chile

Abstract

To determine whether thistles growing at crop edges act as a putative refuge for natural enemies, the seasonal relative abundance of aphidophagous coccinellids was estimated at 0, 10 and 25 m from the edges of three alfalfa fields. Mark-recapture studies were carried out using the trace element rubidium (Rb) to determine whether coccinellids moved between the edges and the alfalfa. The most common aphidophagous coccinellid species were Hippodamia convergens (63%), H. variegata (11%), Rhyzobius lophantae (4%) and Adalia angulifera (4%). In mid-November, the abundance of coccinellids at the edge of (0 m from the edge) the alfalfa plot increased compared to that at the center of the field (25 m from the edge), coinciding with a reduction in the population of aphids at all sampling points. Of the coccinellids captured at the thistle edge, 68% were marked with rubidium, suggesting movement of coccinellids from the alfalfa plot to the thistle growing at its edges. After the thistles were removed, coccinellids returned to the crop, as shown by the presence of marked coccinellids within the alfalfa fields at all three sampling distances. The results of this study suggest that thistles can act as a refuge for coccinellids when aphids are not available in the alfalfa fields.

Effects of Aphid Density and Plant Taxa on Predatory Ladybeetle Abundance at Field and Landscape Scales

“…This result was consistent with the population growth of aphids in maize fields and the concomitant decrease in aphid densities in cotton fields from July to August. Similar prey-motivated changes in habitat selection by ladybeetles tracking high aphid densities have been observed for other ladybeetle species [ 1 , 21 , 75 ]. Additionally, crop phenology or temperature shifts can cause the population movement of natural enemies, for instance, maizeplants at whorl stage offer suitable micro-climatic conditions forforaging ladybeetlesand could act as a refuge during seasonally hot or dry conditions in agro-ecosystems of northern China [ 76 ].…”

“…Most of generalist predatory ladybeetle adults and larvae rely on aphids as a large part of their diets, although they may occasionally use alternative floral resources such as plant pollen and nectar at low aphid density [ 14 , 15 , 16 , 17 ]. Adult ladybeetles usually disperse to various habitats and lay eggs on diversifyinghost plant species to utilize aphid preys during the same season [ 9 ], and their mobility is critical in enabling them to cope with transient and unpredictable food resources that are scattered in both space and time [ 9 , 18 , 19 , 20 , 21 ]. Aphidophagous ladybeetle adults are highly mobile but become less active and lay eggs at sites with high aphid densities to provide adequate food resources to larvae [ 1 , 22 , 23 , 24 , 25 ].…”

Flora surrounding rice fields as a source of alternative prey for coccinellids feeding on the pests of rice

“…In this study the movement of coccinellids from rice to weeds was especially marked just before the rice harvest, which also corresponds with a decline in the hopper populations both in the wet and dry seasons (Win et al, 2011). Villegas et al (2013) report similar movements of coccinellids from thistles in fi eld margins into alfalfa fi elds, which is synchronised with the changes in the availability of prey on the crop and weeds. The coccinellid population moving from weeds caused a reduction in the aphid population on alfalfa during November.…”

Agroecology of a salad crop pest in New Zealand

“…The results found here suggest that S. flava and most parasitoid wasp species found in this system feed on buckwheat and can be marked. Many articles have used rubidium to mark and record the consequences of insect movement since Scarratt's (2008) work (Villegas et al, 2013;Klick et al, 2015;Madeira & Pons, 2015 but they tend to focus on just the beneficial insects. This study was conducted to find the behaviour consequences of the pest and natural enemies through observing their movement so that flowering plants (buckwheat) could be deployed more effectively.…”