Artificial selection for aphid tolerance in the polyphagous predator Lepthyphantes tenuis.
Abstract
Insight into the capacity of natural enemies to control pests may lead to wiser pest management, including a reduction in the use of pesticides. The presence of polyphagous predators may contribute to the control of aphid populations and thereby prevent outbreaks. Many arthropod generalist predators have a limited tolerance to the consumption of aphids. However, differences exist between and within species in the ability to cope with an aphid diet; some within-species variation could be due to genetic differences between individuals. In order to demonstrate additive genetic variation in aphid tolerance, a breeding programme was carried out where offspring of field-collected females of the linyphiid spider Lepthyphantes tenuis were selected for survival on a pure diet of the aphid Rhopalosiphum padi through the first juvenile instar. Aphid tolerance was estimated as the survival in proportion to survival of a control line, fed mixed collembola. Development and reproduction were recorded in order to detect possible selection effects. After only one generation of selection, survival to the first moult on an aphid diet was significantly improved. The aphid tolerance of the first instar spiderlings increased by 63% and a high heritability for the trait was found. An F2 control group derived from selected parents had significantly reduced survival compared with an F2 control group derived from control parents. Developmental rate and reproduction were lower in the selected group than in the control line, demonstrating a cost of tolerance to aphids. The background of the genetic variation and its possible implications for the natural limitation of aphid populations in agricultural systems is discussed. Consideration of the control potential of polyphagous predators must include their genetic variation in aphid tolerance. Management practices aimed at augmenting specialist aphid predators, e.g. by erecting banks or cover crops containing non-pest aphids, may provide selection pressure for increased aphid tolerance in polyphagous predators.