Progeny Sex Ratio Research Articles

Effect of Native and Non-native Hosts on the Biology of <I>Acerophagus papayae</I> Noyes and Schauff, the Introduced Parasitoid of <I>Paracoccus marginatus</I> Williams and Granara De Willink

The bioecology study of any parasitoid using alternative hosts imposes divergent selection pressures on parasitoid populations. In this study, we investigated the bioecology potential of parasitoid <em>Acerophagus papayae</em> Noyes and Schauff on papaya mealybug <em>Paracoccus marginatus</em> Williams and Granara De Willink from different plant hosts. The parameters studied were adult longevity (survival of progeny), fecundity and productivity of female mealybugs and sex ratio of progenies of <em>P. marginatus</em>. The results showed significant differences in bioecology of parasitoid on their natal host (<em>P. marginatus</em> from papaya) compared with the non-natal hosts (<em>P. marginatus</em> from non papaya hosts). It is also compared with honey concentration solution and potato sprouts. The parasitoid is well adapted to the natal host that is papaya compared to others host. However, parasitoids showed a similar high fitness on both natal and non natal hosts. This results could be used to increase the effectiveness of biological control programme on different views.

Effect of Native and Non-native Hosts on the Biology of <I>Acerophagus papayae</I> Noyes and Schauff, the Introduced Parasitoid of <I>Paracoccus marginatus</I> Williams and Granara De Willink

The bioecology study of any parasitoid using alternative hosts imposes divergent selection pressures on parasitoid populations. In this study, we investigated the bioecology potential of parasitoid Acerophagus papayae Noyes and Schauff on papaya mealybug Paracoccus marginatus Williams and Granara De Willink from different plant hosts. The parameters studied were adult longevity (survival of progeny), fecundity and productivity of female mealybugs and sex ratio of progenies of P. marginatus . The results showed significant differences in bioecology of parasitoid on their natal host ( P. marginatus from papaya) compared with the non-natal hosts ( P. marginatus from non papaya hosts). It is also compared with honey concentration solution and potato sprouts. The parasitoid is well adapted to the natal host that is papaya compared to others host. However, parasitoids showed a similar high fitness on both natal and non natal hosts. This results could be used to increase the effectiveness of biological control programme on different views.

Patch exploitation strategies of parasitoids under indirect intra‐ and inter‐specific competition

1. Insect parasitoids are expected to evolve behavioural strategies to exploit resources in competitive environments optimally. Indirect competition between parasitoids is particularly common because exploited host patches remain available in the environment for other foraging individuals.2. The effects of indirect competition on the behaviour of two closely related generalist egg parasitoids were investigated: Trichogramma pintoi Voegelé and Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae). Patch residence time, a patch‐leaving mechanism, and progeny sex allocation of females foraging were analysed: (i) alone, (ii) in patches partially parasitised by conspecifics, and (iii) in patches partially parasitised by heterospecifics.3. Each species responded differently to indirect competition. Trichogramma pintoi females shortened their patch residence times, but they did not adjust their progeny sex ratios. In contrast, T. minutum females did not modify their patch residence times, but they did increase their progeny sex ratios in response to competition. Both Trichogramma species used host rejection, either by antenna rejection or by ovipositor rejection, as a patch‐leaving mechanism.4. In agreement with a companion study of direct competition using the same model species, the present results indicate that even amongst closely related species, responses to competition can vary considerably.

Trade-Off Between Fitness Gain and Cost Determines Profitability of a Peach Aphid Parasitoid.

Aphidius colemani (Viereck) (Hymenoptera: Aphidiidae) is commercially produced and utilized for biological control of peach aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) on greenhouse crops in many countries. To provide knowledge for the evaluation of parasitoid-host interactions and development of effective mass rearing programs, we investigated how and why host age or size affected fitness gain in A. colemani We show that the parasitoid was significantly more likely to encounter larger hosts and that an encounter almost always triggered an attack attempt. However, the attack attempt did not proportionally translate into oviposition because larger aphids had greater ability to defend themselves and the parasitoid spent more time in handling larger aphids. The host age at parasitization had no effect on emergence rates and sex ratio of parasitoid progeny, suggesting that pupae and larvae have similar survival rate in hosts of different ages and/or the parasitoid females do not adjust sex allocation based on host size. When parasitizing mid-aged hosts, the parasitoid gained maximum fitness for their progeny in developmental period, body size, and parasitism. Taking all findings together, we suggest that parasitizing mid-aged green peach aphid nymphs is most profitable for A. colemani.

Sex ratios, virginity, and local resource enhancement in a quasisocial parasitoid

AbstractSclerodermus harmandi (Buysson) (Hymenoptera: Bethylidae) is an economically beneficial species of parasitoid wasp that has an unusual level of sociality: groups of female foundresses reproduce on a single host and exhibit cooperative post‐ovipositional brood care. The beneficial effects females have on each other's reproductive success provide, via the theory of local resource enhancement (LRE), an explanation for their female‐biased progeny sex ratios, which is part of the same framework for understanding sex‐ratio evolution as the more often invoked theory of local mate competition (LMC). Here, we show that S. harmandi sex ratios are overdispersed, with high variance largely attributable to the common occurrence (60%) of developmental mortality. Developmental mortality is also positively associated with the proportion of broods which contain only females at emergence (virgin broods). Virginity is more common when broods are produced by fewer foundresses. Virginity is expected to be disadvantageous under LRE, as it is under LMC, but theory for LRE is less extensively developed. We suggest approaches for the development of LRE theory, in particular using models of ‘population elasticity’ in which the intensity of kin competition is reduced because extra resources are available to local populations that are more cooperative. For S. harmandi, such extra resources may include large hosts that can only be successfully utilised if multiple foundresses cooperate.

PARTIALLY CONSTRAINED SEX ALLOCATION AND THE INDIRECT EFFECTS OF ASSISTED REPRODUCTIVE TECHNOLOGIES ON THE HUMAN SEX RATIO.

Infertility affects around 15% of human couples and in many countries approximately 1-4% of babies are born following Assisted Reproductive Technologies (ART). Several ART techniques are used and these differentially affect the sex ratio of offspring successfully produced. These direct effects on sex ratio also have the potential to influence, indirectly, the sex ratios of offspring born to untreated couples. This is of concern because human sex ratio bias may adversely affect public health. Here the extent of indirect effects of ART that could operate, via Fisherian frequency-dependent natural selection, on the progeny sex ratio of unassisted members of a population is heuristically modelled. Given the degrees to which ART techniques bias sex ratios directly, it is predicted that well over 20% of couples would have to reproduce via ART for there to be any discernible effect on the sex ratios produced, in response, by the remainder of the population. This value is greater than the estimated prevalence of infertility problems among human couples. It is concluded that providing ART to couples with fertility problems does not currently generate significant ethical issues or public health concern in terms of indirect effects on the offspring sex ratios of untreated couples.

Better-surviving barn swallow mothers produce more and better-surviving sons.

Sex allocation theory predicts that parents are selected to bias their progeny sex ratio (SR) toward the sex that will benefit the most from parental quality. Because parental quality may differentially affect survival of sons and daughters, a pivotal test of the adaptive value of SR adjustment is whether parents overproduce offspring of the sex that accrues larger fitness advantages from high parental quality. However, this crucial test of the long-term fitness consequences of sex allocation decisions has seldom been performed. In this study of the barn swallow (Hirundo rustica), we showed a positive correlation between the proportion of sons and maternal annual survival. We then experimentally demonstrated that this association did not depend on the differential costs of rearing offspring of either sex. Finally, we showed that maternal lifespan positively predicted lifespan of sons but not of daughters. Because in barn swallows lifespan is a strong determinant of lifetime reproductive success, the results suggest that mothers overproduce offspring of the sex that benefits the most from maternal quality. Hence, irrespective of mechanisms causing the SR bias and mother-son covariation in lifespan, we provide strong evidence that sex allocation decisions of mothers can highly impact on their lifetime fitness.

Effect of temperature on the developmental time, survival of immatures and adult longevity of Aganaspis daci (Hymenoptera: Figitidae), a natural enemy of Ceratitis capitata (Diptera: Tephritidae)

Longevity, developmental time and offspring survival of parasitoid wasps are decisive in their effective performance as biocontrol agents. Optimum temperature range determines parasitoid survival, development and reproduction. Thus, controlling this abiotic factor is a key to the success of pest management programs. Adult longevity, developmental time from egg to adult and survival of immatures of Aganaspis daci were assessed in the laboratory under different constant temperatures; adult longevity without hosts, but with the provision of water and honey, and developmental time and survival of immatures from host pupae, whose larvae had been exposed to parasitoids. Results showed that longevity depended on temperature decreasing in the range 15–20 °C (36 – 25 days), but was lower in the range 25–35 °C (10 – 7 days). Regarding developmental time from egg to adult and survival of immatures, our results showed that 20 and 25 °C are the most suitable temperatures. At 15 and 30 °C mortality of the immature stages was very high (>90%) or developmental time to adult was very slow (>3 months). Immatures did not survive at 35 °C. We found no significant differences in developmental time to adult or survival of immatures between 20 and 25 °C. The sex ratio of parasitoid progeny was female biased at 25 °C; the proportion of females increased at all cases with temperature. The to and K for total development were 8.5 °C and 500 DD, respectively. Our findings provide some guidance for future inundative or inoculative field releases of this parasitoid for the management of Ceratitis capitata in Spain.

Rapid evolution of a Y-chromosome heterochromatin protein underlies sex chromosome meiotic drive

Sex chromosome meiotic drive, the non-Mendelian transmission of sex chromosomes, is the expression of an intragenomic conflict that can have extreme evolutionary consequences. However, the molecular bases of such conflicts remain poorly understood. Here, we show that a young and rapidly evolving X-linked heterochromatin protein 1 (HP1) gene, HP1D2, plays a key role in the classical Paris sex-ratio (SR) meiotic drive occurring in Drosophila simulans Driver HP1D2 alleles prevent the segregation of the Y chromatids during meiosis II, causing female-biased sex ratio in progeny. HP1D2 accumulates on the heterochromatic Y chromosome in male germ cells, strongly suggesting that it controls the segregation of sister chromatids through heterochromatin modification. We show that Paris SR drive is a consequence of dysfunctional HP1D2 alleles that fail to prepare the Y chromosome for meiosis, thus providing evidence that the rapid evolution of genes controlling the heterochromatin structure can be a significant source of intragenomic conflicts.

Developmental exposures to an azole fungicide triadimenol at environmentally relevant concentrations cause reproductive dysfunction in females of medaka fish

Triadimenol is an effective meatabolite derived from the triazole fungicide triadimenfon. It is an agriculturally important reagent of environmentally emerging concern because of its broad use, persistent occurrence in the environment and greater fungicidal or toxic potency than the parent compound. However, the ecotoxicological impact of triadimenol on fish populations remains unclear. In this study, we investigated developmental toxicity and endocrine disruption effects in medaka fish (Oryzias latipes) exposed at an early life stage to triadimenol. First, mortality, gross development and oxidative stress responses were assessed with triadimenol exposure (3–3000 μg/L) during the embryonic stage. Then, medaka at a sensitive stage of early sexual development underwent 35-day continuous chronic exposure to triadimenol, and the endocrine disruption effects were assessed in adulthood and the next generation. Embryonic exposure to triadimenol did not induce significant teratogenic effects or oxidative stress in embryos or hatchlings. However, early-life exposure to triadimenol under environmentally relevant concentrations (3–30 μg/L) and 300 μg/L persistently altered ovary development and reproduction in female adults and skewed the sex ratio in progeny. As well, triadimenol exposure interrupted the hormone balance, as seen by the expression of genes responsible for estrogen metabolism and egg reproduction. Environmentally relevant triadimenol exposure in medaka fish at early life stages may have ecotoxicological impact in aquatic environments. Along with previous studies, we suggest that conazoles share similar modes of action in disrupting hormone homeostasis and reproduction in fish and mammals.

Life History Traits of the Liverwort HerbivoreScatopsciara cunicularius(Diptera: Sciaridae)

We studied the behavior, life cycle, and reproductive biology of the sciarid fly Scatopsciara cunicularius (Lengersdorf, 1943) under two constant temperatures . The sciarid was reared at 12.3 ± 0.6°C and 22 ± 1.7°C on its host, the liverwort Marchantia polymorpha L. Our results show that the sciarid fly is able to complete its life cycle with liverwort tissue as its only source of food. The egg-laying potential of the insect ranged from 70–174 eggs per female (mean 110 ± 31 eggs). Reproduction was digenic, meaning that one female can produce both male and female progeny. The overall sex ratio did not depart from 1:1, although the progeny sex ratio was highly variable. The developmental period of S. cunicularius was considerably longer in the colder than the warmer temperature. Mean development time of the egg, larva, and pupal stages, and adult longevity in the warm regime was 4, 20, 4, and 5 d, whereas mean development time of each juvenile stage and adult longevity in the cold regime was 13, 95, 11, and 8 d, respectively. The results suggest that the phenology of S. cunicularius is temperature dependent. Scatopsciara cunicularius could constitute a promising agent for biological control of M. polymorpha .

Reproductive and developmental biology of the emerald ash borer parasitoid Spathius galinae (Hymenoptera: Braconidae) as affected by temperature

Emerald ash borer Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) is an invasive pest of serious concern in North America. To complement ongoing biological control efforts, Spathius galinae Belokobylskij and Strazenac (Hymenoptera: Braconidae), a recently-described specialist parasitoid of emerald ash borer larvae, is being released for the first time in the United States. To better understand its reproductive and developmental biology, and to improve outcomes of mass-rearing, we investigated the effects of constant ambient temperature (15, 20, 25, 30, and 35°C) on immature development time, sex ratio, pre-oviposition period, fecundity and survivorship. Results show that between 20 and 30°C immature development time was inversely associated with temperature, with adults emerging ≈38, 32, and 25d after oviposition at 20, 25, and 30°C, respectively. At 15°C larvae developed to 5th instars and spun cocoons before development was arrested, while at 35°C parasitoid eggs desiccated and did not hatch. Sex ratio of adult progeny that were exposed to different temperatures, from eggs, was not affected. When newly (⩽24h-old) emerged female parasitoids were provided larval hosts throughout their lifetimes, adults parasitized at all temperatures except 35°C, although parasitism rate was highest (35%), as was lifetime fecundity (43 progeny/female), when females lived at 25°C. Survivorship was inversely associated with temperature, with ovipositing females living for >60d when maintained at 15°C, and females held at 35°C living for <10d. Life table analyses showed S. galinae had the highest net reproductive rate (R0=27.8) and intrinsic rate of increase (rm=0.29) when female parasitoids were maintained at 25°C for their lifetimes, suggesting this is the optimal temperature to rear S. galinae.

Quality deterioration of mass reared offsprings of Bracon hebetor in successive generations

A study was undertaken to determine the generation-wise parasitizing efficiency of mass reared Bracon hebetor on wax moth (Galleria mellonella). Two experiments were conducted to achieve the objectives. In the first experiment, the host larvae and parasitoid were released in the field micro plot during first generation and reared in the laboratory in subsequent generations. In another experiment, all generations were developed in the laboratory. In the first experiment, generation showed significant variation on sex ratio of adult progeny production. The male sex ratio increased with the range of 62.89 to 74.58% and female sex ratio declined ranging from 39 to 25% with the advancement of generations. The percent parasitization and adult progeny production was not influenced appreciably with the progress of generation. In the second experiment parasitization and adult progeny production did not vary significantly in successive generations. However there was a decreasing trend in parasitization from 95 to 55% by Bracon hebetor and adult progeny production by 47.5 to 15.5 adultsfemale-110 larvae-1 over generation. The sex ratio of adult progeny was significantly influenced by inbreed generation in laboratory reared population. Female decrease in sex ratio from first to sixth generation was 39.25 to 16.88%.SAARC J. Agri., 13(2): 1-12 (2015)

Effect of host density on life table statistics of Bracon hebetor Say, 1836 (Hymenoptera: Braconidae)

Bracon hebetor Say shows high fecundity and natural rate of increase which makes it a promising enemy against Corcyra cephalonica, a very common stored grain pest. The functional response of the parasitoid can determine potential of a species to act as a biocontrol agent; it defines parasitoid’s searching efficiency and provides an understanding of host–parasitoid interaction. The mean longevity of female parasitoids had no significant difference when maintained at different densities of host insects. However, progeny sex ratio was significantly affected when different host densities were maintained during its adult life. The net fecundity rate (R0) and total fecundity rate (Rt) were highest when host density was five hosts per reproductive chamber. The mean length of generation time (T.c.) was higher on host density one compared to other densities. The intrinsic rate of increase (rm) was highest when the host density was five and lowest on 20 hosts per reproductive chamber. Other life table parameters we...

Effect of female vs. male pupa of Scirpophaga excerptalis Walker on reproductive potential of Tetrastichus howardi (Olliff) (Hynenoptera: Eulophidae)

Tetrastichus howardi (Olliff) (Eulophidae: Hymenoptera) is gregarious and polyphagous endopupal parasitoid associated with sugarcane stem borers. It is adapted in its host-searching strategy to penetrate tunnels excavated by stem borers which is a prerequisite for a good biological control agent of stem borers. The experiment was conducted at 25 ± 2°C and 65 ± 5% relative humidity in BOD with ten replications at Biological in Division of Crop Protection, ICAR, Lucknow. The number of adult emerged (81.29) from female pupa (81.29) was more than male pupa (65.30). The smaller host pupae (i.e. male pupa) gave rise to small number of parasitoids whereas larger ones (i.e. female pupa) supported development of more parasitoids. The parasitoid completed development in 19.5 days on both pupae. There was no significant difference of development period in male vs. female pupa. The female emergence (%) on female and male pupa was 86.94 and 74.23, respectively. The number and sex ratio of adult progeny emerging from host pupa depends on the size. The large host size is more beneficial to the fitness of daughters than to sons and selection would then favor wasps to lay more daughters in large hosts and more sons in small hosts. It is concluded that parasitoid had high reproductive potential, more female biasesd sex ratio and its gregarious development make possible to multiply on sugarcane top borer in the laboratory.

Mass rearing of Bracon hebetor (Hym.: Braconidae) on wax moth, Galleria mellonella (Lep.: Pyralidae) with varying density of parasitoid and the host

Rearing methods for Bracon hebetor (Say) (Hym., Braconidae) were investigated in the series of laboratory experiments designed to enhance the yield of the mass rearing of this parasitoid for biological control of lepidopteran field and stored product pests. In these experiments, the effects of parasitoid and host densities on fertility and sex ratio of B. hebetor were assessed. In parasitoid densities, 50 last-instar greater wax moth (GWM) Galleria mellonella (L.) larvae were placed per container and 1, 2, 4, 8 or10 pairs of B. hebetor (one male and one female) were released in each container. In host density study two pairs B. hebetor were introduce in six different densities (10, 20, 30, 40, 50 and 60) of host, GWM per container. A density of ten male-female pairs of B. hebetor produced a higher number of progeny (205 ± 7.07 adults) on 50 last instar larvae of GWM. Similarly, in a host density experiment, a density of 60 last instars GWM larvae produced a significantly higher number of parasitoid progeny (142.0 ± 8.75 adults), followed by 50 last instar larvae (141.0 ± 8.34 adults) among the tested host densities when two pairs of B. hebetor were used. The sex ratio of progenies was male-biased in all studies and there were no significant effects on sex ratio in various parasitoid and host densities. In mass rearing experiment, total number of emerged parasitoids per 200 wax moth larvae was 1091 ± 82.38 adults with mean parasitism rate of 98 ± 0.8%.

Effect of temperature on the reproductive biology of Peristenus spretus (Hymenoptera: Braconidae), a biological control agent of the plant bug Apolygus lucorum (Hemiptera: Miridae)

Peristenus spretus Chen et van Achterberg (Hymenoptera: Braconidae), a parasitoid of the plant bug Apolygus lucorum (Hemiptera: Miridae), has been studied for use in augmentative biological control in China. Under laboratory conditions, we explored the development, survival, age-specific and potential lifetime fecundity, oviposition period and progeny sex ratio of P. spretus reared at six constant temperatures (15°C, 19°C, 23°C, 27°C, 31°C, 35°C) on the second instar nymphs of A. lucorum. At 15°C, male and female P. spretus took 48.7 ± 0.3 and 52.5 ± 0.3 days to complete their immature development, while developmental time was reduced by more than half at 23°C and 27°C. The parasitoid can only develop to the larval stage at 31°C and neither larva nor pupa survived at 35°C. The estimated lower developmental threshold of the immature stage was 7.3°C. When parasitoid adults were exposed at 15°C, females laid 90% of their eggs at first 19 days of oviposition and had an extended reproductive life. In contrast, females held at 27°C laid most of their eggs (90%) in their first of 10 days of oviposition and had shorter longevity. The highest potential lifetime fecundity of P. spretus was 671.2 ± 34.7 SE eggs produced over 23.4 ± 1.4 SE days at 23°C. At 15°C, 19°C and 23°C, sex ratios of reared parasitoids were male-biased, but at 27°C there was no male bias.

The impact of nest tube dimensions on reproduction parameters in a cavity nesting solitary bee, Osmia bicornis (Hymenoptera: Megachilidae)

Recent declines of bee populations have led to great interest in preserving bee species and fuel efforts to develop solitary species for pollination purposes. Xylophilous solitary bees can be easily reared in artificial nests tubes for commercial agricultural as well as wild plant pollination. The impact of the dimensions of these artificial nest tubes on reproduction parameters was studied in the red mason bee, Osmia bicornis (L.), in a long-term study. Increasing tube diameter positively affected both progeny sex ratio and body size. Sex ratio, but not progeny body mass, was negatively affected by short tube length. Building costs rose with increasing diameter accompanied by deteriorated efficiency of tube space utilization. Although female bees used a wide spectrum of nest dimensions, artificial nest tubes of 8–10 mm internal diameter and a length of at least 150 mm were optimal.

Effect of Mutual Interference on the Ability of Spalangia cameroni (Hymenoptera: Pteromalidae) to Attack and Parasitize Pupae of Stomoxys calcitrans (Diptera: Muscidae).

We investigated the effect of mutual interference on the attack efficiency and the rate of successful parasitism on the parasitoid Spalangia cameroni (Perkins) attacking pupae of the stable fly Stomoxys calcitrans (L.). Female parasitoids (2, 4, 8, 16, or 32) were exposed to 100 fly pupae during 24 h. The number of pupae that were attacked and the number successfully parasitized increased with the parasitoid density and reached a maximum of ∼70 and 50, respectively. Parasitoid-induced mortality (PIM) was about 20 pupae, irrespective of parasitoid density. The per capita rates of attack, successful parasitism and parasitoid-induced mortality declined monotonously with parasitoid density. Progeny sex ratio was female biased for all parasitoid densities, but declined significantly with increasing parasitoid density from ∼70% females at the lowest density to ∼60% at the highest. Mutual interference was incorporated into a functional response model to predict the attack rate and the rate of successful parasitism at different temperatures, host densities and parasitoid densities. The model explained 93.5% of the variation in the observed number of attacked pupae and 91.5% of the variation in the number of successfully parasitized pupae. The model predicts that increasing parasitoid densities will increase the percentage of killed hosts, but only up to a certain density. Above this density, a further increase in parasitoid abundance will actually lead to a decline in the percentage parasitism. These findings may have some implications for using S. cameroni in biological control against flies using inundative releases.

Effect of letrozole on masculinization of Siamese fighting fish (Betta splendens)

The aim of this study was to evaluate the effect of letrozole (a non-steroidal aromatase inhibitor) on masculinization of Siamese fighting fish (Betta splendens). Different doses of letrozole 50, 100, 150 and 200 ppm (mg/kg feed) were incorporated into diet and fed for periods of 30, 40 or 50 days. Immersion treatment of letrozole at selected doses (250, 500, 750 and 1,000?g/l) for 3 h each on third, fifth and eighth day-post-hatching (dph) (Trial 1) and fourth, sixth and eighth dph (Trial 2) was given.The oral administration of letrozole for 30, 40 or 50 days did not have any significant effect on the sex ratio of B. splendens. The immersion treatment of letrozole induced 100% masculinization at 500 and 1000?g/l in trial 1, while it yielded only 66.66 and 90% male population at 500 and 1000 ?g/l in Trial 2. The dietary administration of letrozole for 30 and 50 days caused tail deformities and/or rudimentary and absence of dorsal fin. The progeny testing of males from letrozole treated (both oral and immersion) groups indicate that the sex ratio of progenies of each of the males tested did not differ significantly from that of control, indicating that all those males carried XY genotype. Letrozole treatments suppressed ovarian development (atretic oocytes were common). However, the testicular development was unaffected. The study revealed that immersion treatment of letrozole was more effective in inducing masculinization of B. splendens than the oral administration of letrozole.