Weighty matters: Body size, diet and specialization in aphidophagous ladybird beetles (Coleoptera: Coccinellidae)

Abstract

Abstract. Aphidophagous ladybirds exhibit a broad range of body sizes. Until now this has been thought to be a function of the different prey densities that they feed at, with smaller ladybirds feeding at lower prey densities. The size of the prey species they feed on has been considered to have no relationship with ladybird body size. However, these arguments possess a limited capacity to explain observed data from the field. I here demonstrate a more realistic, complex approach incorporating both prey density and the size of prey species. Small ladybirds can feed on small aphids at both low and high densities. However when the aphid species is large they cannot catch the older, bigger, more energy-rich aphid instars due to their small size. They are thus unable to feed on large aphid prey at low densities, although at higher densities numbers of the smaller instars may be sufficient to sustain them. By contrast large ladybirds can feed on large aphids at both low and high densities due to their superior ability to catch the bigger, more energyrich older aphids; however they cannot be sustained by low densities of small aphids due to food limitation consequent on their large size. This more complex association between ladybird size, prey size and prey density possesses a better explanatory power for earlier field data. Because of this relationship, ladybird body size also provides an important trade-off determining dietary breadth and specialization in the aphidophagous Coccinellidae. Dietary specialists more closely match the size of their limited prey species, have higher overall capture efficiencies and can thus continue to reproduce at lower aphid densities for longer. By contrast dietary generalists adopt a one-size-fits-all strategy, are medium-sized and have lower capture efficiencies of individual prey species, thus requiring higher aphid densities. The role of body-size in dietary specialization is supported by data from the British fauna. Rather than trade-offs related to prey chemistry, which have hitherto been the centre of attention, body size trade-offs are the likely most important universal factor underlying dietary specialization in aphidophagous coccinellids.

Food Relationships

“…The turning point may be represented by the concept of Sloggett (2008b) : ' body size trade -offs are the likely most important universal factor underlying dietary specialization in aphidophagous coccinellids ' . As our short explanation here will necessarily remain a simplifi cation, the reader is advised to study directly the two recent papers by Sloggett (2008a, b) , which contain many stimulating thoughts.…”

“…Alternative food will be discussed Anatis ocellata , but kicked away the small Myrrha octodecimguttata . A further size -related dilemma commented upon by Sloggett (2008b) is that of the relation between body size of aphidophagous ladybirds and aphid density and size. While Dixon ' s (2007) model considers only prey density (Fig.…”

“…While Dixon ' s (2007) model considers only prey density (Fig. 5.2 a), Sloggett (2008b) argues that the relationship is more complex and comprises both prey size and prey density (Fig. 5.2 b, c).…”

Eating chemically defended prey: alkaloid metabolism in an invasive ladybird predator of other ladybirds (Coleoptera: Coccinellidae)

“…High metabolic specificity might be expected to lead to strong genetic trade-offs in the tolerance of different prey defensive chemicals, leading to a higher degree of prey specialisation. The limited evidence relating to prey chemistrybased trade-offs in invertebrate predators is mixed (Albuquerque et al, 1997;Sadeghi and Gilbert, 1999;Pekár et al, 2008), and in aphidophagous ladybirds such trade-offs have been suggested to be of limited importance compared with trade-offs related to prey capture, notably body size (Sloggett, 2008a, Sloggett, 2008b. Clearly additional work is required to link metabolic tolerance and the role of trade-offs in predators.…”

Mother-Offspring Relations: Prey Quality and Maternal Size Affect Egg Size of an Acariphagous Lady Beetle in Culture

“…For example, large-sized coccinellids, such as Adalia species and Coccinella species, produce small eggs relative to their body size, whereas tiny-sized Stethorus species produce large eggs relative to their body size [9,11]. Differences in egg size between small and large species might be an adaptation to the size of their prey and the size of prey aggregations on host plants [11][12][13]. It may also reflect the oviposition strategies of a species (i.e., degree of synovigeny, number of ovarioles present in a species, and rate of egg maturation).…”