Multiple mating is a behaviour observed across various polyandrous insect species. It is suggested that, in ladybirds, this strategy of multiple copulations is used to enhance fecundity and fertility through sperm replenishment. Studies on sperm depletion need to correlate fertility with the presence of spermatozoa in the spermatheca. This study investigates the role of sperm replenishment in the ladybird Cryptolaemus montrouzieri. We hypothesised that females of this species exhibit fecundity and fertility rates proportional to the number of sperm replenishment opportunities (constant, periodic or absent). We observed oviposition behaviour and hatching rates over 30 days, and simultaneously tested for sperm depletion in females that copulated once. We dissected the spermathecae at four post-copulation moments to count spermatozoa under a microscope. Our results indicate that a single copulation suffices to maintain fertility for at least 30 days. Females with constant replenishment opportunities exhibited higher fecundity but lower fertility and increased mortality, suggesting a reproductive cost associated with frequent mating. Females with no replenishment during the experiment, exhibited the highest hatchability rate and lowest oviposition. Periodic copulation resulted in optimal female mating rate, with average fertility and fecundity. A plausible hypothesis would be that paired females choose to fertilise fewer eggs from a single male but are unable to control the effects of the oviposition stimulus induced by the male's presence. These findings have implications for the management and rearing of C. montrouzieri in biological control programmes, optimizing mating strategies for mass production.

The long-lived polygynandrous ladybird beetle Tenuisvalvae notata (Mulsant) found in Brazil was evaluated in the laboratory for the effects of multiple mating and aging on its reproductive performance. This species is native to South America and is an important predator of mealybugs. Specifically studied were partner choice, female reproductive success, adult longevity, male virility, and offspring development. Young (5–10 days old) and older virgin females (95–100 days old) were subjected to either a single mate or multiple mating with the same or different males of various mating status (virgin or previously mated once, twice, and thrice). Results revealed a preference in both genders to mate with previously known partners. Additionally, younger females had higher fecundity and greater longevity when mated only once in comparison to those mated multiple times. Fecundity, fertility, and offspring development were similar across the treatments regardless of the number of mating or male mating history. Fecundity and fertility decreased throughout the oviposition period regardless of mating treatment.

The costs and benefits of polyandry are still not well understood. We studied the effects of multiple mating on the reproductive performance of female Brontispa longissima (Coleoptera: Chrysomelidae), one of the most serious pests of the coconut palm, by using three experimental treatments: (1) singly-mated females (single treatment); (2) females that mated 10 times with the same male (repetition treatment); and (3) females that mated once with each of 10 different males (polyandry treatment). Both multiple mating treatments resulted in significantly greater total egg production and the proportion of eggs that successfully hatched (hatching success) than with the single mating treatment. Furthermore, the polyandry treatment resulted in greater total egg production and hatching success than with the repetition treatment. Thus, mate diversity may affect the direct and indirect benefits of multiple mating. Female longevity, the length of the preoviposition period, the length of the period from emergence to termination of oviposition, and the length of the ovipositing period did not differ among treatments. The pronounced fecundity and fertility benefits that females gain from multiple mating, coupled with a lack of longevity costs, apparently explain the extreme polyandry in B. longissima.

Field and laboratory observations were carried out to understand the significance of prolonged copulation and the male substance transferred from males to females in the white grub beetle Dasylepida ishigakiensis Niijima & Kinoshita. Adults emerged from the soil in the evening and formed mating pairs on sugarcane plants, where copulation lasted for 1–3 h. Mating pairs (30%) observed in the field were accompanied by one or two additional males. Some females mated with one such male after ending copulation with the first male, showing multiple mating. After mating, males dropped to the ground to burrow into the soil earlier than females. Females received a large amount of colloidal secretion from males during mating. The amount and rate of transfer of this secretion from males to females were investigated in this study. Transfer of the secretion from males to females was completed within 30 min, and females that had mated with two males in the laboratory stored a larger amount of male secretion in the bursa copulatrix than those that had mated once. The results of both field and laboratory observations might indicate a possibility that prolonged copulation serves as a post-insemination female guarding behaviour to prevent mating by other conspecific males.

Odonates (dragonflies) are well known for the ability of the males to displace sperm stored in the female's sperm-storage organs during copulation. By this means, copulating males are able to increase their fertilization success. This ability has been used as an example to illustrate a conflict of interests between the sexes in which males have evolved sperm-displacement mechanisms whilst females have presumably evolved means to avoid sperm displacement. The present review has four aims: (1) to describe the copulatory mechanisms used during sperm displacement; (2) to analyse the causes of sperm usage patterns; (3) to discuss this information using current hypotheses on conflict between the sexes; and (4) to illuminate topics for further research. Four copulatory mechanisms are described: sperm removal (physical withdrawal of stored sperm), sperm repositioning (‘pushing’ of rival sperm to sites where its use will be least likely), female sensory stimulation to induce sperm ejection, and sperm flushing (displacement of sperm using the copulating male's sperm). Sperm-precedence studies in Odonata are scarce and their values vary considerably between species. In those species in which sperm displacement is incomplete, the last copulating male obtains a high but variable short-term fertilization success which decreases with time. Some male and female factors affecting sperm precedence patterns are mentioned: (1) male variation in genital morphology; (2) duration of copulation influenced by the male (the longer the copulation, the more stored sperm displaced); (3) adaptations of the sperm-storage organs that allow the female to manipulate the sperm she has received (i.e. avoiding sperm displacement, re-distributing sperm masses, favouring sperm located in certain sites and ejecting sperm after copulation). We suggest that male and female odonates have co-evolved at the level of genital function with the control of stored sperm as the focus of the conflict. The benefits for males in this co-evolution lie in maximizing their fertilization success. However, it is not clear what females obtain from storing sperm and making it unreachable during sperm displacement. Two hypothetical benefits that females may obtain for which some evidence has been gathered are genetic diversity and viability genes. It is finally suggested that odonates can become excellent subjects of study for testing current ideas related to sexual conflict and speciation processes through sexual selection.

The aim of this review is to consider the potential benefits that females may gain from mating more than once in a single reproductive cycle. The relationship between non-genetic and genetic benefits is briefly explored. We suggest that multiple mating for purely non-genetic benefits is unlikely as it invariably leads to the possibility of genetic benefits as well. We begin by briefly reviewing the main models for genetic benefits to mate choice, and the supporting evidence that choice can increase offspring performance and the sexual attractiveness of sons. We then explain how multiple mating can elevate offspring fitness by increasing the number of potential sires that compete, when this occurs in conjunction with mechanisms of paternity biasing that function in copula or post-copulation. We begin by identifying cases where females use pre-copulatory cues to identify mates prior to remating. In the simplest case, females remate because they identify a superior mate and ‘trade up’ genetically. The main evidence for this process comes from extra-pair copulation in birds. Second, we note other cases where pre-copulatory cues may be less reliable and females mate with several males to promote post-copulatory mechanisms that bias paternity. Although a distinction is drawn between sperm competition and cryptic female choice, we point out that the genetic benefits to polyandry in terms of producing more viable or sexually attractive offspring do not depend on the exact mechanism that leads to biased paternity. Post-copulatory mechanisms of paternity biasing may: (1) reduce genetic incompatibility between male and female genetic contributions to offspring; (2) increase offspring viability if there is a positive correlation between traits favoured post-copulation and those that improve performance under natural selection; (3) increase the ability of sons to gain paternity when they mate with polyandrous females. A third possibility is that genetic diversity among offspring is directly favoured. This can be due to bet-hedging (due to mate assessment errors or temporal fluctuations in the environment), beneficial interactions between less related siblings or the opportunity to preferentially fertilise eggs with sperm of a specific genotype drawn from a range of stored sperm depending on prevailing environmental conditions. We use case studies from the social insects to provide some concrete examples of the role of genetic diversity among progeny in elevating fitness. We conclude that post-copulatory mechanisms provide a more reliable way of selecting a genetically compatible mate than pre-copulatory mate choice. Some of the best evidence for cryptic female choice by sperm selection is due to selection of more compatible sperm. Two future areas of research seem likely to be profitable. First, more experimental evidence is needed demonstrating that multiple mating increases offspring fitness via genetic gains. Second, the role of multiple mating in promoting assortative fertilization and increasing reproductive isolation between populations may help us to understand sympatric speciation.