Ovarian dynamics and specialisation in ladybirds

Abstract

1. Generalist predatory insects that exploit unpredictable and ephemeral prey should allocate metabolic resources differently to soma and gonads than specialist species. As the former have more opportunities to encounter a wide array of prey than specialists, the expectation is that they will more rapidly resorb oocytes when food is scarce. By doing so, they reallocate resources to the soma to support the search for oviposition sites of a better quality. Similarly, they are expected to resume oogenesis faster than the specialist when good conditions return.2. This hypothesis was tested by comparing a generalist and a specialist ladybird species belonging to the same genus.3. A resorption index was calculated for females of both species subjected to several starvation regimes. This index indicated that over a period of fasting of 3 days, the intensity of resorption was greater in the generalist than the specialist. When food was again supplied, oogenesis resumed and within 1 day was faster in the generalist than in the specialist.4. As predicted, the resorption of oocytes and replenishment occurred faster in the generalist than in the specialist species. This is the first time, to our knowledge, that the speed and intensity of the ovarian dynamics of a predatory insect have been linked to its way of life.

Habitat or prey specialization in predatory ladybird beetles: a case study of two closely related species

“…In addition, the state of development of the gonads of females, which within a few days is known to reflect the quality of the food supply (Osawa ; Ferrer et al. ), did not differ in the two species after 2 weeks of consuming cereal and pea aphids. This was unexpected because cereal and pea aphids are not recorded in the natural prey range of A. decempunctata and contain different plant secondary metabolites which A. decempunctata normally never encounters in the wild (Dixon ; Pasteels ).…”

“…Oocytes in the first category are not being resorbed, while those with indices of 2 to 5 indicate a growing incidence of resorption (Ferrer et al. ). Resorption indicates that females are not eating or eating unsuitable food and therefore resorbing oocyte yolk to sustain energy expenditure (Osawa ; Ferrer et al.…”

“…Resorption indicates that females are not eating or eating unsuitable food and therefore resorbing oocyte yolk to sustain energy expenditure (Osawa ; Ferrer et al. ). The proportions of oocytes in each category were compared using a chi‐square test.…”

“…In addition, these differences in the range of resources they each exploit are associated with differences in the ovarian dynamics of these species of ladybird (Ferrer et al. ).…”

Behavioural and physiological responses to prey-related cues reflect higher competitiveness of invasive vs. native ladybirds

“…Oosorption occurs with the occurrence of an unfavourable environment, including food shortage and starvation 38–40 . Under these conditions, ladybird females resorb nutrients from developing oocytes, investing resources in survival rather than reproduction.…”