Induction of reproductive diapause in Hippodamia convergens (Coleoptera: Coccinellidae) hinges on prey quality and availability

Abstract

Abstract. In the High Plains of western Kansas, USA, the convergent lady beetle Hippodamia convergens Guérin completes a spring generation feeding on cereal aphids in winter wheat before leaving fields in large numbers around the time of harvest. In late May, large aggregations of coccinellids form on wild sunflowers, Helianthus annuus, and certain other weeds, that appear to serve as important sources of water absorption for the beetles, and other beneficial insects, during the dry prairie summer. Adult beetles were collected from sunflower plants and held in four treatments: (1) access to water only, (2) access to sunflower stalks only, (3) eggs of Ephestia kuehniella provided ad libitum + water and, (4) greenbug, Schizaphis graminum Rondani provided ad libitum. Most females fed greenbug matured eggs in less than a week and only a few entered reproductive diapause. In contrast, more than half of the females fed Ephestia eggs, an inferior diet, entered reproductive diapause, and those that matured eggs required an average of almost three weeks to do so. Time to 50% mortality was 7 days for beetles receiving only water, and 12 days for those receiving only sunflower stalks, whereupon all survivors were fed greenbug. Even after feeding on greenbugs for a month, less than half of the surviving females in these two treatments produced eggs. We conclude that reproductive diapause is an important adaptation for improving H. convergens survival during summer when aphids are scarce, although females will forgo diapause if they have continuous access to high quality prey.

Food Relationships

“…Aphidophages thus apparently feed with less than full and in how well they support reproduction (e.g. Omkar & James 2004, Michaud & Qureshi 2005. Effects of the foods depend on the physical conditions (e.g.…”

Chemical cues mediating aphid location by natural enemies

“…While ladybirds and other aphid natural enemies frequently visit plants for purposes such as nectar or pollen feeding, and may be attracted to these plants in the absence of aphids (e.g. Michaud & Qureshi, 2005), laboratory studies have often failed to show attraction to undamaged plants. For example, the ladybird (Coleoptera: Coccinellidae) species Coccinella septempunctata L. (Ninkovic et al, 2001) and Adalia bipunctata (L.) (Francis et al, 2004), and the hoverfly Episyrphus balteatus (DeGeer) (Diptera: Syrphidae) (Francis et al, 2005b) were not attracted to odours from their (undamaged) host plant.…”

Why is Coccinella septempunctata so successful? (A point-of-view)

“…In other cases, particular plants may be attractive to many coccinellid species because they supply valuable resources in the absence of prey. Examples include the attraction of C. maculata to maize (Zea mays) in the absence of aphid infestation, and the attraction of numerous coccinellid species to the extra-floral nectaries of sunflower, Helianthus annuus (Michaud & Qureshi, 2005). When the density of aphids is low in alfalfa (Medicago sativa), C7 adults aggregate in local concentrations of the alfalfa weevil (Hypera postica), although weevil larvae serve only as supplemental food (Evans & Toller, 2007).…”