In most countries, men are more likely to be childless than women. Understanding how this inequality arises is important given the significance of parenthood for individuals’ lives. The objective of this study was to explore how three prominent explanations for sex inequalities in childlessness relate to the Sex Gap in Childlessness (SGC) in Sweden. The three explanations examined were sex ratio imbalance (more men than women), mismeasurement of fatherhood (inequalities in registration) and partnership differences (inequality in multi-partner fertility). Administrative register data for cohorts born in 1945–1974 were used. The population was restricted to men and women who were born in Sweden or arrived prior to the age of 15, and all registered childbearing partnerships were examined. To explore the possible significance of the three explanations, counter-factual standardization was used. Of the three explanations examined, the population sex ratio had the largest positive impact on the SGC, while multi-partner fertility had a negative impact. The results show that inequalities in the sex ratio can explain about 20–34% of the SGC depending on cohort. Inequalities in registration of fathers explain about 9–24% of the SGC depending on cohort. Finally, results show that women are slightly more likely to have multiple partners, and that this behaviour has a substantial minimizing effect on the SGC (minimizing it by 6–65%). To the authors’ knowledge this was the first paper to estimate the scope of the impacts of these three mechanisms on the SGC. Differences in multi-partner fertility have in many instances been used as an explanation for men’s higher childlessness. This study shows that women have slightly more childbearing partners than men, and that this actually leads to a smaller SGC in the studied population.

Like the northern periphery regions of other Arctic countries, the Russian North had a higher male–female sex ratio than the rest of the country. During the two decades following the breakup of the Soviet Union, the male sex ratio in the Russian North declined considerably, from 101 males per 100 females in 1989 to 92 in 2010. The regions and population of the Russian North were greatly impacted by the shift in northern development approaches from the centrally planned system of the Soviet Union to the market-oriented system of Russia. This paper examines the decline in the male population in the Russian North based on data from the 1989, 2002 and 2010 population censuses. The paper finds that only one quarter of the decline in the male sex ratio in the Russian North can be attributed to higher male outmigration and that three quarters are the result of significantly higher and widening gaps between females and males in life expectancy. The conclusion is that men in the Russian North coped with the social and economic upheavals by dying prematurely not by migrating. The leading causes of death for men were cardiovascular diseases and external causes such as murder, suicide and accidents.

Despite an overall downward trend in child sex ratios in India, some of the most imbalanced districts in 2001 (fewer girls than boys) showed signs of becoming more balanced in 2011. This analysis looked in depth at these districts to better understand the nature of the improvement in the child sex ratio using two rounds of data from the Census of India from 2001 and 2011. Data were used from the 153 districts that showed improvement in their child sex ratio between 2001 and 2011. The improvement was decomposed into: (1) less sex-selective abortion and (2) improved girl compared with boy mortality. Most of the improvement in child sex ratios were shown to be due to reductions in sex-selective abortion, although this still made up the majority of the cause of imbalanced sex ratios in 2011. Child sex ratio improvement has been happening in both rural and urban areas of India, and there is evidence of stagnation in mortality decline for urban girls.

In China, owing to many parents' preference for sons, the sex ratio at birth (SRB) is imbalanced. During the 2000s, SRB fluctuated at around 120 boys to 100 girls. In the early 2000s, to tackle the SRB imbalance, the Chinese government launched a series of policy measures under the banner of “care for girls.” This article presents a case study of the Care for Girls programme in order to explore how the construction of SRB as a social problem has led to the formulation and adoption of one set of policy responses to the exclusion of others. The analysis shows that the imbalanced SRB has been attributed to rural peoples' cultural and economic deficiencies rather than cast in terms of a need to recognize the inherent worth of girls or a need to ensure that all rural families have entitlements to basic social welfare. This construction of SRB has enabled the Party-state to advance a “care as control” policy response which comprises ideological education, conditional material benefits and sanctions, and which sidesteps the institutional underpinnings of the problem.

Fellman and Eriksson (2010) cited my suggestion that the sex ratio (proportion male) of monozygotic (MZ) twins is lower than that of dizygotic (DZ) twins (James 1975). Here I offer elaborations on and potential explanations for this.

We describe levels of parasitism of ectoparasitic bat flies (Hippoboscoidea: Streblidae) on male and female bats from an extensive Neotropical survey. The collection resulted from coordinated vertebrate-parasite surveys undertaken by the Smithsonian Venezuelan Project (SVP) from 1965–1968, which sexed 24 978 bats of 130 species. Streblid parasites were recovered from 6935 individuals of 87 bat species, but only 47 species were captured frequently enough (≥ 20 infested individuals) to permit reliable estimates of streblid parasitism on males and females. Well-sampled species included 39 phyllostomids, four mormoopids, two noctilionids, one natalid and one molossid. Prevalence of streblid parasitism (proportion of individuals infested) of male and female bats was generally not significantly different, and averaged 0.34 across infested species. In species-level analyses assessed against captures, significant sex differences in infestation levels were noted in six species; all had mean prevalence below 0.5 and females were parasitized disproportionately in each. Sex differences in total numbers of flies were noted in 21 species, and in 16 of these, females carried disproportionately heavy loads. Sex differences were also found for eight species of bat in the number of fly species infesting an individual; seven of eight showed heavier female parasitism. In analyses weighted by infestation levels, sex differences in total number of flies were found in only 12 species, with seven showing excessive parasitism of females, and no species showed sex differences in the number of fly species infesting them. These significant biases were not associated with sexual size dimorphism among the bat species. Generally higher levels of parasitism among female bats accords with theory, given their generally higher survivorship and enhanced probabilities of lateral and vertical transmission of host-specific parasites, but contrasts with patterns shown by many other parasitic arthropods. Future analyses should target social groupings of bats, not passively sampled foragers, to better address the mechanisms responsible for this pattern.

Many species exhibit skewed sex ratios at birth. Here we investigate the relationships between environmental and maternal variables (as surrogates for maternal condition) and foetal sex in African buffalo Syncerus caffer and elephant Loxodonta africana of the Kruger National Park, South Africa. Using logistic regression no significant effect was found of year, maternal lactational status, maternal age, rainfall or density on foetal sex ratio. Using a subset of our data, it was also concluded that maternal body condition did not affect foetal sex ratio in buffalo. Our analyses failed to support hypotheses predicting that mothers will skew the sex ratios of their offspring in relation to their body condition. In this study, buffalo and elephant produced offspring with a sex ratio close to parity. Our results are discussed in light of the implications for testing such hypotheses in analyses of population level.

Progeny production and sex ratios of the parasitoids Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) and its exotic congener Cotesia flavipes Cameron (Hymenoptera: Braconidae) emerging from three species of field-collected stemborers were compared. There were no significant differences in numbers of progeny of the two parasitoids from the African stemborers, Chilo orichalcociliellus (Strand) (Lepidoptera: Pyralidae) and Sesamia calamistis Hampson (Lepidoptera: Noctuidae). Cotesia flavipes produced more progeny than C. sesamiae on large larvae of its coevolved Asian host, Chilo partellus (Swinhoe). No significant differences in the number of parasitoid progeny were observed for different-sized Ch. orichalcociliellus or S. calamistis larvae. These data suggest that under field conditions, Co. flavipes may be superior to Co. sesamiae as a parasitoid of its co-evolved host, Ch. partellus.

The biconical trap of Challier and Laveissièr was compared with Langridge's box screen (LBS) and Moloo's awning screen skirt (ASS) for relative efficiency in catching the tsetse species, Glossina pallidipes Austen, in two areas in Kenya. The dark blue biconical trap performed better than the ASS in one area, but both of them caught more males than females. In the other area, the sky blue version of the biconical gave higher yields than LBS and the white biconical. In both areas, the white biconical trap caught the highest proportion of old flies, while ASS caught the highest proportion of young flies. The biconical trap is preferable because it is collapsible, easy to handle and transport, and needs minimal manpower to operate, unlike the LBS and ASS.