Male-biased Sex Ratio Research Articles

Cross-Cultural Variation in women’s Preferences for men’s Body Hair

According to the ectoparasite avoidance hypothesis, natural selection has shaped human hairlessness to reduce the potential for the body to host disease carrying ectoparasites. However, men retain sexually dimorphic and conspicuous patches of facial and body hair. The ectoparasite avoidance hypothesis also proposes that sexual selection via women’s mate preferences for reduced hirsutism has further elaborated upon the reduction in body hair and could explain variation in women’s preferences for body hair in men. The current study tests this hypothesis using cross-cultural data from 30 countries on women’s preferences for chest hair. We test whether heterosexual women’s (N = 3436) preferences for reduced hirsutism are most pronounced in countries with higher disease and parasite levels or whether other social and economic factors previously shown to influence preferences for facial masculinity and beardedness predict women’s preferences for chest hair. We found that preferences were unrelated to past or current disease rates. Instead, preferences for body hair were stronger among women who were older, had strong preferences for facial hair, and were from countries that had male-biased sex ratios, higher human development indices, and lower education indices. Women’s body hair preferences were also associated with facial masculinity preferences and gender empowerment. However, neither these terms, nor human development indices or education indices were individually significant in their contributions to the family of best-fit models and we suggest caution when interpreting their significance. Women’s preferences for body hair may be strongest among women from countries where male-male competition is higher and preferences for beardedness are stronger rather than where prevailing ecological conditions my impact on maternal and offspring survival.

Performance of Newly Described Native Edible Cricket Scapsipedus icipe (Orthoptera: Gryllidae) on Various Diets of Relevance for Farming.

A new native edible cricket species, Scapsipedus icipe Hugel and Tanga, has been described in Kenya for the first time. However, there is lack of information on suitable diets and their effects on the developmental time, survival, weight gain, body length, growth index, preoviposition, oviposition, postoviposition, fecundity, egg eclosion period, adult emergence, and longevity of this species, which are prerequisite for large-scale production. In this study, six diets (wheat bran, soybean, fish offal, pumpkin leaf, carrot, and maize meals) selected to vary in protein, carbohydrate, and fat content were evaluated. The developmental time and survival rate of the different life stages varied considerably on the various diets, with the shortest development and highest survival rate recorded when fed wheat bran diet. Preoviposition duration was significantly longer on maize and carrot diets (>10 d) compared with that recorded on the other diets (<8 d). Body weight and body length were significantly influenced by the different diets tested. Females of S. icipe fed on protein-rich diets (fish offal, soybean, and wheat bran) had significantly higher lifetime fecundity and fertility. Female-biased sex ratio was recorded on wheat bran and soybean diets, whereas male-biased sex ratio was recorded on maize and carrot diets. Our findings reveal that the impact of diet quality on the biological fitness parameters of S. icipe and the implication of the results are discussed in light of effective mass rearing of this species.

A short note on extreme sex ratio in solitary bees Osmia cornuta in semi-field trials testing the impact of neonicotinoids

The widespread prophylactic use of neonicotinoids has severe negative effects on non-target organisms that provide ecosystem services. Chronic neonicotinoid exposure led to a male-biased offspring sex ratio in the solitary bee species Osmia bicornis in laboratory experiments, but semi-field or field data are largely lacking. Here, we used semi-field experiments to investigate the potential impact of the neonicotinoid clothianidin on the sex ratio of the closely related species Osmia cornuta. Male and female individuals of O. cornuta were held in flight cages with fully blooming winter oilseed rape, treated or not with clothianidin. After hibernation, sex ratio of emerging offspring and overwintering mortality was determined. A total of 191 male and 4 female, and 203 male and 2 female O. cornuta emerged in the control and the clothianidin treatment, respectively, thereby clearly showing an extremely male-biased sex ratio. However, there was no significant clothianidin treatment effect. As sex ratio was strongly biased in both, the clothianidin and the control treatment, our data can obviously not explain the underlying mechanism. Such extreme sex ratios require more attention in semi-field studies assessing the impacts of pesticides and other stressors on solitary bees.

Why so many Agta boys? Explaining 'extreme' sex ratios in Philippine foragers.

Male-biased sex ratios have been observed in multiple small-scale societies. Although intentional and systematic female-biased mortality has been posited as an explanation, there is often a lack of ethnographic evidence of systematic female neglect and/or infanticide. The Agta, a foraging population from the Philippines, have a skewed sex ratio of 1.29 (129 males per 100 females) aged 15 years or under. We hypothesised that this skew was not caused by greater female deaths, but due to an adaptive response, where more males were produced at birth in reaction to high male-biased extrinsic mortality. To test this hypothesis we utilise census, childcare and mortality data from 915 Agta. The Agta's sex ratio is significantly male-biased in the <1 (n = 48, 2:1) and 1-5 year (n = 170, 1.39:1) age cohorts; however, we find no evidence of systematic female neglect in patterns of childcare. Furthermore, the sex ratio decreases over cohorts, becoming balanced by the end of the juvenile period, owing to significantly higher male mortality. Taken together, these results are not supportive of female infanticide or neglect, and instead suggest an adaptive mechanism, acting in utero as a response to male-biased juvenile mortality, following Fisherian principles of equalising parental investment.

What has happened to the females? Population trends in the Aesculapian snake at its northern range limit

Populations at the edge of their main range of distribution are often exposed to suboptimal environments. They therefore exhibit a greater susceptibility towards habitat changes and often clearly differ in their structure and dynamics from populations in the main range. Here we define population parameters of the Aesculapian snake Zamenis longissimus, a species endangered in Europe, at its northern range limit based on data obtained in the valley of the River San (Bieszczady Mts., SE Poland) in 2009-2013. We focus on the spatial and temporal sex ratio patterns by comparing data obtained in 2009-2013 with published records from 1990 to 1998 and five other northern populations (1 from the main range, 1 at the northern edge of its contiguous range, and 3 entirely isolated ones). Using the capture-mark-recapture (CMR) method, we estimated the population size to be about 230 snakes. Our data show that among adults the percentage of females (17.74%) in the San valley population was significantly lower than in those other five populations and the same population studied two decades earlier. Because of the male-biased sex ratio, we estimated the effective population size to be about 74 snakes. This disproportion between the sexes in adults may be interpreted as an early stage of the population extinction process at the northern range limit of this species’ distribution. It is probably due to the limited availability of egg-laying sites, compelling females to undertake longer movements, which may heighten the risk of mortality.

What Makes Her a Material Girl?: The Influence of Childhood Economic Background and Sex Ratio on Female Preference for Male Resource Availability.

Drawing on life history theory, this research explores the moderating role of childhood economic background in the relationship between sex ratio and the female's mate preference for male resource availability. Using different priming materials, three experiments consistently found that women with a rich childhood economic background showed a stable level of mate preference for good resource-this applied regardless of male- or female-biased sex ratio. But females with a poor childhood economic background showed a higher level of preference for male resource availability under the condition of female-biased sex ratio (vs. the condition of male-biased sex ratio). These findings support the moderating role of female childhood economic background in the relationship between sex ratio and their mating preference of good resources.

Spatial variation in sex ratio and density explains subtle changes in the strength of size-assortative mating in Edessa contermina (Hemiptera: Pentatomidae)

Size-assortative mating (SAM) is usually explained by the mate-choice hypothesis. However, this hypothesis does not consider the effects of variations in the intensity of mating competition on mate choice and SAM. For example, in populations with male-biased operational sex ratios (OSR) and high densities, large males will have more advantages during mating competition and will have access to the most mating opportunities with large, preferred females (i.e. mating competition hypothesis). In this study, we investigated the effects of mating competition and mate choice on the strength of SAM in Edessa contermina (Hemiptera: Pentatomidae). We also described sexual size dimorphism and the mating system of this Neotropical stink bug in a conservation area of the Brazilian savanna. We used density as a proxy for mating competition intensity because it was positively correlated with OSR. Size-assortative mating was more consistent under intense mating competition. However, males copulated with relatively larger females as population density increased. Males assortatively mated based on size in the first and second copulation events observed, while both female matings were random. Thus, male mate choice may promote SAM in E. contermina, but its strength is affected by variations in the intensity of mating competition. Hence, we provided empirical support for mating competition as a potential mechanism promoting subtle changes in SAM. We discussed potential implications of this mechanism on the mating patterns of pentatomids.

Population structure leads to male-biased population sex ratios under environmental sex determination.

Spatial structure has been shown to favor female-biased sex allocation, but current theory fails to explain male biases seen in many taxa, particularly those with environmental sex determination (ESD). We present a theory and accompanying individual-based simulation model that demonstrates how population structure leads to male-biased population sex ratios under ESD. Our simulations agree with earlier work showing that the high productivity of female-producing habitats creates a net influx of sex-determining alleles into male-producing habitats, causing larger sex ratio biases, and lower productivity in male-producing environments (Harts etal. 2014). In contrast to previous findings, we show that male-biasing habitats disproportionately impact the global sex ratio, resulting in stable male-biased population sex ratios under ESD. The failure to detect a male bias in earlier work can be attributed to small subpopulation sizes leading to local mate competition, a condition unlikely to be met in most ESD systems. Simulations revealed that consistent male biases are expected over a wide range of population structures, environmental conditions, and genetic architectures of sex determination, with male excesses as large as 30 percent under some conditions. Given the ubiquity of genetic structure in natural populations, we predict that modest, enduring male biased allocation should be common in ESD species, a pattern consistent with reviews of ESD sex ratios.

Geographic origin and migration phenology of European red admirals (Vanessa atalanta) as revealed by stable isotopes

BackgroundLong-distance migration has evolved multiple times in different animal taxa. For insect migrants, the complete annual migration cycle covering several thousand kilometres, may be performed by several generations, each migrating part of the distance and reproducing. Different life-cycle stages and preferred orientation may thus, be found along the migration route. For migrating red admirals (Vanessa atalanta) it has been questioned if they reproduce in the most northern part of the range. Here we present migration phenology data from a two-year time series of migrating red admirals captured at Rybachy, Kaliningrad, in the northern part of Europe investigating time for migration, life-history stage (migration, reproduction) as well as site of origin in individual butterflies.MethodsRed admirals were captured daily at a coastal site during spring, summer and autumn in 2004 and 2005. For the sampled individuals, reproductive status and fuel content were estimated by visual inspection, and hydrogen isotopes (δ2H) were analysed in wing samples. δ2H values was compared with samples from two nearby reference sites in Estonia and Poland.ResultsAnalysis of hydrogen isotopes (δ2H) in red admiral wings showed that the spring cohort were of a southerly origin, while those caught in August or later in the autumn were from the local region or areas further to the north. All females caught during spring had developing eggs in their abdomen, but no eggs were found in late summer/autumn. There was a male-biased sex ratio during autumn and a difference in lipid content between years. When comparing the isotopic data with inland nearby locations, it was clear that the range of δ2H values (− 181 to − 78) was wider at Rybachy as compared to the two reference sites in Estonia and Poland (− 174 to − 100).ConclusionsDuring spring, migratory female red admirals arrived from the south and were ready to reproduce, while the autumn passage mainly engaged local and more northern individuals carrying large fuel deposits in preparation for long-distance migration. The phenology data suggest that individuals select to migrate in favourable weather conditions and that numbers may differ between years. Future studies should focus on individual sampling at a wide range of sites to reveal differential migration strategies and timing of migration between sexes and populations of migrating butterflies.

Body size variation in the sexually dimorphic scaphopod Rhabdus rectius (Carpenter, 1864) (Dentaliida: Rhabdidae)

ABSTRACTMale-biased sexual size dimorphism typically evolves via sexual selection for larger males that are favoured by choosy females or are more successful in mate competition with other males. Among marine invertebrates that broadcast their gametes into the ocean for fertilisation, this form of sexual size dimorphism is rare because such species lack direct interactions among males or between the sexes. However, the broadcast-spawning tusk shell Rhabdus rectius was recently reported to show strong male-biased sexual size dimorphism. That pattern might imply interesting and undiscovered sexual selection in this species. We found instead that the distribution of body size variation (weight, shell length) was similar between males and females of R. rectius, and mean sizes were not different between the sexes. However, we noted a male-biased sex ratio (∼1:1.3) in our large sample of individuals. Many live scaphopods (and several dead shells) showed partial or complete boreholes drilled by predatory gastropods. Boreholes were observed on males and females in similar proportions. We collected scaphopods along with multiple individuals of one likely scaphopod predator, the small moon snail Euspira pallida, and in the lab we observed successful attacks by moon snails on tusk shells.

Interactions Between Facultative Symbionts Hamiltonella and Cardinium in Bemisia tabaci (Hemiptera: Aleyrodoidea): Cooperation or Conflict?

Maternally-inherited facultative symbionts are widespread in most insect species, and it is common that several symbionts coexist in the same host individual. Hence, the symbionts may compete or share for the limited resources and space in the host. The whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodoidea), harbors a diverse array of facultative symbionts, among which Hamiltonella sp. and Cardinium sp. are abundant species. Hamiltonella alone increases host fitness, while Cardinium alone confers lower fitness. Locking those different partners together creates ideal situations for the evolution of interactions between symbionts. In this study, we compared the fitness effects of whiteflies infected with only Hamiltonella to Hamiltonella-Cardnium co-infected whiteflies and measured the density of Hamiltonella and Cardinium during host aging, aiming to explore Hamiltonella-Cardinium interactions in B. tabaci. Our results illustrated that Hamiltonella-Cardinium coinfection induced lower fecundity, egg hatchability and number of female offspring, leading to a male-biased sex ratio in offspring, while there is no evidence for reproductive incompatibility between the infections. We also found an antagonistic interaction between Hamiltonella and Cardinium given that the density of the latter increased across time and led to a decrease of Hamiltonella density, which may be the underlying causes of the fitness cost in double-infected B. tabaci. Exploring the ecological consequences of co-infections of these different symbionts helps us to understand the nature of host-symbiont interactions in this species and potential for evolutionary conflict.

Elevated potential for intraspecific competition in territorial carnivores occupying fragmented landscapes

The distribution of mammals is determined by a suite of endogenous and exogenous factors. In territorial, polygynous species like tigers (Panthera tigris), males often center their space-use around female territories, repelling competitors from these areas. Competition among males for females leads to increased mortality of both sexes and infanticide of unrelated cubs, which can lead to population declines. We hypothesized that increased territorial overlap among adult male tigers and elevated levels of inter and intra-sex competition would be manifest in populations with male-biased adult sex ratios (ASR). We also assessed whether inter-sex variation in adult survival or degree of habitat connectivity resulted in skewed ASR. We evaluated these hypotheses using camera trap data from three tiger populations occupying habitat patches with varying levels of connectivity and ASRs. Data were analyzed using multi-state occupancy models, where states were defined as habitat use by one or more male tigers in sites with and without female use. As predicted, in populations with male-biased or even ASR we found evidence for increased spatial overlap between male tigers, particularly pronounced in areas adjacent to female territories. Given parity in adult survival, habitat fragmentation likely caused male-biased ASR. Our results suggest that the persistence of small tiger populations in habitat patches with male-biased ASR may be significantly compromised by behavior-mediated endogenous demographic processes that are often overlooked. In habitat fragments with pronounced male biased ASR, population recovery of territorial carnivores may require timely supplementation of individuals to compensate for population losses from intraspecific competition.

Genetic Monogamy in Socially Monogamous Mammals Is Primarily Predicted by Multiple Life History Factors: A Meta-Analysis

Background We still do not understand the key drivers or prevalence of genetic monogamy in mammals despite the amount of attention that the evolution of mammalian monogamy has received. There have been numerous reviews of the hypotheses proposed to explain monogamy, some of which focused on animals in general, while others focused on particular classes like birds or mammals, or on specific orders within a class. Because monogamy is rare in mammals overall but relatively common in some of the orders in which it has been observed (e.g., Primates, Macroscelidea and Carnivora), mammals provide a unique taxon in which to study the evolution and maintenance of monogamy However, the term ‘monogamy’ encompasses related but separate phenomena; i.e., social monogamy (pair-living by opposite-sex conspecifics) and genetic monogamy or reproductive monogamy (mating exclusivity). A recent review of mammalian monogamy reported that 226 species (9%) in 9 orders (35%) were socially monogamous, although socially monogamous mammals are not necessarily genetically monogamous. Methods Since factors that predispose socially monogamous mammals to be genetically monogamous are still subject to debate, we conducted meta-analyses using model selection to determine the relative importance of several life history, demographic and environmental factors in predicting genetic monogamy. Results We found sufficient data to include 41 species in our analysis, about 2x more than have been included in previous analyses of mammalian genetic monogamy. We found that living as part of a socially monogamous pair versus in a group was the best predictor of genetic monogamy, either by itself or in combination with high levels of paternal care. A male-biased sex ratio and low population density were inversely related to the number of pairs that were genetically monogamous, but not to the production of intra-pair young or litters. Conclusion Our results agree with the results of some previous analyses but suggest that more than one factor may be important in driving genetic monogamy in mammals.

Sex-Specific Effects of Incubation Temperature on Embryonic Development of Zebra Finch (Taeniopygia guttata) Embryos.

In oviparous species, the embryonic environment-particularly temperature-can alter phenotype and survival of an individual by affecting its size as well as its metabolic rate. Previous studies have shown that incubation temperatures can affect sex ratio in birds; specifically, low incubation temperatures were shown to produce a male-biased sex ratio in zebra finches (Taeniopygia guttata) possibly because of a higher pre- or postnatal mortality rate in females. We hypothesized that sexes respond differently to suboptimal incubation temperature, leading to a male-biased sex ratio. To test this hypothesis, zebra finch eggs were incubated at 36.1°, 37.5°, or 38.5°C and hatching success, hatchling mass, residual yolk mass, and pectoralis mass were measured. We found that while hatchling mass was similar between the sexes at 37.5°C, female hatchlings were heavier at 36.1°C, and male hatchlings were heavier at 38.5°C. Pectoralis muscle mass was similar between the sexes at 36.1°C; however, at 37.5°C, female pectoralis mass was heavier at hatching than that of males. Females at 37.5°C also had lower residual yolk at hatching compared with males, reflecting a higher use of energy by female embryos compared with male embryos at this temperature. In contrast, residual yolk was similar between the sexes at 36.1° and 38.5°C. Our results suggest that there are sex differences in how incubation temperature alters organ mass and yolk energy reserve; this can lead to a difference in survival at different incubation temperatures between the sexes. Taken together with previous studies showing that females alter incubation behavior with ambient temperature, rising ambient temperatures could impact phenotype and survival of avian offspring in a sex-specific manner.

Pseudoparasitism by Spalangia cameroni (Hymenoptera: Pteromalidae) of pupae of Ceratitis capitata (Diptera: Tephritidae): Frequency and implications

The effectiveness of natural enemies in controlling pests may be determined by many traits linked to their ability to regulate the density of their prey. In this respect, the phenomenon of pseudoparasitism, in which female parasitoids reject a host after inserting their ovipositor into it, is fairly common among hymenopteran parasitoids. However, in spite of this its effect on hosts is rarely reported in entomological and biological control literature. For this reason, in the present study, the pseudoparasitism by the parasitoid Spalangia cameroni Perkins of the Mediterranean pest Ceratitis capitata (Wiedemann) and its effect on several biological parameters of the host were studied under laboratory conditions. The results indicate that the percentage pseudoparasitism by S. cameroni of medfly in the laboratory is high, even slightly higher than host-feeding, which is commonly used to evaluate the potential of parasitoids as biological control agents. In addition, the adults that emerge from pseudoparasitized medfly pupae have a male-biased sex ratio, low levels of survival and are frequently damaged, which results in small adults and an inability to mate successfully. In conclusion, our results indicate that pseudoparasitism is common and enhances the effectiveness of S. cameroni attacking medfly, which highlights the importance of this phenomenon when selecting parasitoids to be included in a biological control programme.

Sex ratio and density may affect temporal variation in size-assortative mating in a Neotropical ant species

Size-assortative mating (SAM) is common in animals, especially in insects, owing to the influence of body size on mate choice and fitness in both sexes. According to sexual selection theory, choosiness in mate selection may decrease when the costs of intrasexual competition and mate choice increase. Thus, scenarios with intense mating competition (i.e. with high population density and highly biased sex ratio) should weaken SAM. In this study, we tested this hypothesis in mating aggregations of the ant Tranopelta gilva. During mating swarm, population density and male-bias in sex ratios may increase with time, promoting changes in SAM. Considering this potential variation in SAM, we hypothesized that (a) T. gilva ants assortatively mate by size when male mating competition is weak; (b) larger males win most intrasexual disputes; and (c) there is no significant variation in body size among individuals arriving earlier and later during mating aggregations. We attracted winged ants to open plastic arenas, placed under artificial light at night in a protected area of the Brazilian Savanna. Two intensities of mating competition were comparatively evaluated in the arenas: ‘weakly competitive’ (low ant density and a slightly male-biased sex ratio) and ‘intense competitive’ conditions (high ant density and strongly male-biased sex ratio). Assortative mating in T. gilva occurred only when mating competition was weak. Male size was not important in male–male competition and large males did not arrive first at mating aggregations. Because male–male competition did not explain variations in SAM, we suggest that female choice at low densities and male harassment at high densities would explain these variations. In conclusion, mating competition may affect temporal variation in SAM of T. gilva.

The transformer2 gene of the pumpkin fruit fly, Bactrocera tau (Walker), functions in sex determination, male fertility and testis development.

The insect transformer2 (tra2) gene has a prevalent role in cooperating with the sex-determining gene transformer (tra) to direct female differentiation. Here, we report the identification and characterization of Btau-tra2, the tra2 orthologue of the pumpkin fruit fly, Bactrocera tau, an invasive agricultural pest. The Btau-tra2 gene produces three transcript variants. However, only two transcripts can be examined; one is present at all developmental stages in the soma and germline of both sexes and the other one is specific to the embryo and the germline. Knocking down the function of Btau-tra2 produced a male-biased sex ratio and some intersexes. Consistent with a role in sex determination, the obtained intersexual and male sterility phenotypes express a mix of male and female splice variants of the tra and doublesex (dsx) orthologues, indicating that Btau-tra2 has a conserved splicing regulatory function and acts together with/upstream of tra and dsx. In addition, some males obtained from the knock down are fertile but their fertilities are extremely reduced. Moreover, almost all surviving RNA interference (RNAi) males harbour testes having some defects in their external morphologies. Most notably, the body size of a few surviving RNAi flies was two-to threefold increased with respect to the normal size. Our findings suggest that Btau-tra2 is involved in male fertility and may also have an unprecedented role in body size control besides its conserved role in sex determination.

Male-biased sex ratios in Australian migrant populations: a population-based study of 1191250 births 1999-2015.

BackgroundThe naturally occurring male-to-female (M/F) ratio at birth is 1.05. Higher ratios found primarily in countries across Asia have been attributed to prenatal sex selection due to son preference. There is growing evidence that sex-selective practices continue following migration; however, little is known about these practices following migration to Australia.MethodsIn this population-based study we assessed M/F ratios at birth per mother’s country of birth for all registered births 1999–2015 in Victoria, Australia (n = 1 191 250). We also compared the M/F ratio among births to mothers born elsewhere to that of mothers born in Australia, stratified by time period and parity.ResultsCompared with the naturally occurring M/F ratio as well as to the M/F ratio among births to mothers born in Australia, there was an increased ratio of male births to mothers born in India, China and South-East Asia, particularly at higher parities and in more recent time periods (elevated M/F ratios ranged from 1·079 to 1·248, relative risks of male birth ranged from 1·012 to 1·084 with confidence intervals between 1·001 and 1·160 and P-values between 0·005 and 0·039). The most male-biased sex ratios were found among multiple births to Indian-born mothers, and parity of two or more births to Indian and Chinese-born mothers in 2011–15.ConclusionsThe male-biased sex ratios observed in this study indicate that prenatal sex selection may be continuing following migration to Australia from countries where these practices have been documented. The excess of males among multiple births raises the question as to what role assisted reproduction plays. Findings also suggest that systematic discrimination against females starts in the womb.

Nutrient deficiency promotes male-biased apparent sex ratios at the ramet level in the dioecious plant Myrica gale var. tomentosa in oligotrophic environments in bogs.

In populations of dioecious plants, the differences in the cost of reproduction between male and female plants can promote a male-biased sex ratio. In this study, we examine the macronutrient levels in tissues of the dioecious wetland shrub Myrica gale to identify the cost of reproduction for male and female plants and to examine the effect of nutrients on the apparent sex ratio at the ramet level. We examined plants across 12 populations of M. gale inhabiting bogs and fens in Japan. For each population, we used line transects to estimate the apparent sex ratio and measured the concentrations of nitrogen (N), phosphorus (P), and potassium (K) in the leaves sampled from male and female plants and in the fruits from female plants. For five of the populations, we calculated the flowering frequency, mortality, and the recruitment rate (as the rate of clonal propagation). We found that the proportion of females was positively affected, and the male bias of sex ratios reduced, by increases in P concentration in leaves sampled from female plants. Neither mortality nor recruitment was affected by sex or by the nutrient concentration (P, K). The flowering frequency was not affected by sex or by K concentration, but decreased with decreases in the P concentration measured in leaves. This study confirmed that reproduction in M. gale is P-limited. We found no distinct differences in the flowering frequency, mortality, or recruitment rate between the male and female plants.

Dietary methoprene supplement promotes early sexual maturation of male Queensland fruit fly Bactrocera tryoni

Sterile insect technique (SIT) is an environmentally benign pest management technique that relies on released sterile male insects mating with, and curtailing reproduction of, wild females. However, for species with high mortality rates and long adult maturation phases, a large proportion of the released insects can die before maturing and so fail to contribute to SIT. To counter this problem, inclusion of yeast hydrolysate in pre-release diets and treatment of pupae or adults with methoprene, a juvenile hormone analogue, have been investigated as means of accelerating development of some fruit flies, including Queensland fruit fly, Bactrocera tryoni (Froggatt) (‘Q-fly’). Methoprene has most often been administered topically in acetone solution, which is toxic, flammable, and impractical for operational settings. As a practical alternative, we incorporated methoprene (0, 0.05, 0.1, and 0.5%) into Q-fly adult diet of sugar only or sugar mixed with yeast hydrolysate for 2 days, and then provided sugar only for the rest of the trial period. Mating performance of males and females was tested from 4 to 30 days of age. Flies provided sugar mixed with yeast hydrolysate had increased mating propensity in comparison with flies that were provided sugar only. At all ages and for both diets, all methoprene doses increased male mating probability. Methoprene treatment did not affect copula latency of males that received yeast hydrolysate, but males that received only sugar mated earlier if they had received 0.05% methoprene. Methoprene treatment of males was also associated with longer copulations, which may affect fertility of females that later remate. Females differed from males in that methoprene treatment did not significantly affect mating probability or latency, but resembled males in that methoprene treatment resulted in longer copulations. Sex differences in response to methoprene may lead to male-biased operational sex ratio when bisex Q-fly strains are used in SIT. Yeast hydrolysate increased longevity of both males and females, but methoprene treatment did not affect longevity. Overall, findings of the present study indicate that Q-fly sexual maturation can be accelerated, and SIT might hence be enhanced, by incorporation of methoprene and yeast hydrolysate in pre-release diet.