Host-size-dependent sex ratio theory and improving mass-reared parasitoid sex ratios

2002 ◽  
Vol 24 (1) ◽  
pp. 31-41 ◽  
Author(s):  
Paul J. Ode ◽  
Kevin M. Heinz
Keyword(s):  
Sex Ratio ◽  
Sex Ratios ◽  
Host Size ◽  
Size Dependent ◽  
Sex Ratio Theory

Host size-dependent sex allocation behaviour in a parasitoid: implications forCatolaccus grandis(Hymenoptera: Pteromalidae) mass rearing programmes

1998 ◽  
Vol 88 (1) ◽  
pp. 37-45 ◽  
Author(s):  
K.M. Heinz
Keyword(s):  
Biological Control ◽  
Sex Ratio ◽  
Sex Allocation ◽  
Sex Ratios ◽  
Boll Weevil ◽  
Mass Rearing ◽  
Host Size ◽  
Offspring Sex Ratio ◽  
Offspring Sex ◽  
Control Programmes

AbstractAn often encountered problem associated with augmentative and inundative biological control programmes is the high cost of producing sufficient numbers of natural enemies necessary to suppress pest populations within the time constraints imposed by ephemeral agroecosystems. In many arrhenotokous parasitoids, overproduction of males in mass-rearing cultures inflates costs (per female) and thus limits the economic feasibility of these biological control programmes. Within the context of existing production technologies, experiments were conducted to determine if the sex ratio ofCatolaccus grandis(Burks), an ectoparasitoid of the boll weevilAnthonomous grandisBoheman, varied as a function of boll weevil larval size. Results from natural and manipulative experiments demonstrate the following behavioural characteristics associated with C.grandissex allocation behaviour: (i) femaleC. grandisoffspring are produced on large size hosts and male offspring are produced on small hosts; (ii) whether a host is considered large or small depends upon the overall distribution of host sizes encountered by a female parasitoid; and (iii) female parasitoids exhibit a greater rate of increase in body size with host size than do male parasitoids. The observed patterns cannot be explained by sex-specific mortality of immature parasitoids developing on the different host size categories. In subsequent experiments, laboratory cultures ofC. grandisexposed daily to successively larger sizes ofA. grandislarvae produced successively greater female biased offspring sex ratios, cultures exposed daily to successively smaller sizes of host larvae produced successively greater male biased offspring sex ratios, and cultures exposed daily to equivalent host size distributions over time maintained a uniform offspring sex ratio. By increasing the average size ofA. grandislarval hosts exposed toC. grandisby 2.5 mg per day in mass rearing cultures, the percentage of male progeny can be reduced from 33% to 23% over a period of four consecutive exposure days.

Estimating the Frequency of Constrained Sex Allocation in Field Populations of Hymenoptera

Behaviour ◽  
1990 ◽  
Vol 114 (1-4) ◽  
pp. 137-147 ◽  
Author(s):  
H.C.J. Godfray ◽  
I.C.W. Hardy
Keyword(s):  
Sex Ratio ◽  
Sex Allocation ◽  
Sex Ratios ◽  
Parasitoid Species ◽  
Ratio Bias ◽  
Sex Ratio Bias ◽  
Sex Ratio Theory

Abstract1) Sex ratio theory has assumed that females can produce offspring of both sexes. It has been suggested that some females in haplodiploid populations are only able to produce sons (constrained sex allocation), for example because they are virgin. The presence of such females influences the optimal sex ratio of unconstrained females. The relevance of these ideas to field sex ratios is largely untested. 2) The frequencies of constrained oviposition in three Drosophila parasitoid species are estimated. Constrained, ovipositing females were distinguished by the absence of sperm in the spermatheca. Constrained females were absent or rare in these species. 3) We review data from the literature that allow an estimate of the frequency of constrained females. 4) We conclude that the available evidence suggests that while constrained oviposition is uncommon, there are some species in which constrained females are sufficiently common to select for an observable sex ratio bias by unconstrained females.

scholarly journals Extraordinarily precise nematode sex ratios: Adaptive responses to vanishingly rare mating options

2021 ◽  
Author(s):  
Justin Van Goor ◽  
Edward Allen Herre ◽  
Adalberto Gomez ◽  
John D Nason
Keyword(s):  
Sex Ratio ◽  
Sex Ratios ◽  
Nematode Species ◽  
Environmental Sex Determination ◽  
Adaptive Responses ◽  
Wasp Species ◽  
Population Structures ◽  
Subdivided Populations ◽  
Sex Ratio Theory ◽  
Evolutionary Persistence

Sex ratio theory predicts both mean sex ratio and variance under a range of population structures. Here, we compare two genera of phoretic nematodes (Parasitodiplogaster and Ficophagus spp.) associated with twelve fig-pollinating wasp species in Panama. The host wasps exhibit classic Local Mate Competition: only inseminated females disperse from natal figs, and their offspring form mating pools that consist of scores of the adult offspring contributed by one or a few foundress mothers. In contrast, in both nematode genera, only sexually undifferentiated juveniles disperse, and their mating pools routinely consist of eight or fewer adults. Across all mating pool sizes, the sex ratios observed in both nematode genera are consistently female-biased (~0.34 males), which is markedly less female-biased than is often observed in the host wasps (~0.10 males). In further contrast with their hosts, variances in nematode sex ratios are also consistently precise (significantly less than binomial). The constraints associated with predictably small mating pools within highly subdivided populations appear to select for precise sex ratios that contribute both to the reproductive success of individual nematodes, and to the evolutionary persistence of nematode species. We suggest that some form of environmental sex determination underlies these precise sex ratios.

Gametocyte sex ratio in single-clone infections of the malaria parasite Plasmodium mexicanum

Parasitology ◽  
2010 ◽  
Vol 137 (13) ◽  
pp. 1851-1859 ◽  
Author(s):  
A.T. NEAL ◽  
J.J. SCHALL
Keyword(s):  
Genetic Variation ◽  
Sex Ratio ◽  
Malaria Parasite ◽  
Sex Ratios ◽  
Experimental Studies ◽  
Life History Trait ◽  
Gametocyte Density ◽  
Male Gametes ◽  
Single Clone ◽  
Sex Ratio Theory

SUMMARYSex ratio theory predicts that malaria parasites should bias gametocyte production toward female cells in single-clone infections because they will experience complete inbreeding of parasite gametes within the vector. A higher proportion of male gametocytes is favoured under conditions that reduce success of male gametes at reaching females such as low gametocyte density or attack of the immune system later in the infection. Recent experimental studies reveal genetic variation for gametocyte sex ratio in single-clone infections. We examined these issues with a study of experimental single-clone infections for the lizard malaria parasite Plasmodium mexicanum in its natural host. Gametocyte sex ratios of replicate single-clone infections were determined over a period of 3–4 months. Sex ratios were generally female biased, but not as strongly as expected under simple sex ratio theory. Gametocyte density was not related to sex ratio, and male gametocytes did not become more common later in infections. The apparent surplus of male gametocytes could be explained if male fecundity is low in this parasite, or if rapid clotting of the lizard blood reduces male gamete mobility. There was also a significant clone effect on sex ratio, suggesting genetic variation for some life-history trait, possibly male fecundity.

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