Some Factors that Distort the Sex Ratio of the Gypsy Moth Porthetria dispar (L.) (Lepidoptera: Lymantriidae)

1963 ◽  
Vol 95 (5) ◽  
pp. 465-474 ◽  
Author(s):  
Robert W. Campbell

AbstractDuring a study on the population dynamics of the gypsy moth, Porthetria dispar (L.), conducted in the Town of Glenville, New York, some factors were found to affect the sexes differentially. The importance of this differential mortality is indicated by the fact that 78 per cent of the variation in the logarithm of an index of population trend (the ratio of population density from year to year) was associated with the logarithm of adult sex ratio.Disease and desiccation during instars IV-VI and among pre-pupae were strongly selective against the female insects. This differential mortality caused a change in the pupal sex ratio from about 70 per cent females where no disease occurred to less than 25 per cent female pupae following an epizoötic. Ichneumonids, on the other hand, usually killed more male pupae than females, except when host size was reduced by excessive larval density and competition. The net result from this series of factors that distort the sex ratio has been to produce adult sex ratios varying from more than 80 per cent female moths to only 2 per cent females.In this host species, as in most other animals, it seems that the population consequences of a mortality factor that kills the host sexes in different proportions should be evaluated in terms of the more critical (female) sex destroyed.

1963 ◽  
Vol 95 (4) ◽  
pp. 426-434 ◽  
Author(s):  
Robert W. Campbell

AbstractThe population dynamics of the gypsy moth, Porthetria dispar (L.), are being studied on 10 sites in the Town of Glenville, New York. This paper discusses the role of disease and a condition here termed “desiccation” in the dynamics of these populations during a 4-year period, 1958-1961 inclusive.The term “desiccation” refers to dead pre-pupae that appeared shriveled, and were stiff to the touch, and which had a solid mass of food in their gut. The incidence of desiccation among pre-pupae was closely related to the number of eggs per egg mass produced at the end of the generation (a measure of relative insect density).Disease incidence among larval gypsy moth populations was directly related to insect density. Disease incidence was also related to site conditions, with higher mortality occurring in wet sites.When larval populations reached high densities, they always declined from the dense level within a few generations. These declines ranged from a sudden drastic reduction to a much more gradual decline. The former was preceded by virtual food exhaustion, while the latter was not usually preceded by exhaustion of the food supply.Disease and desiccation were primary factors in producing the sudden type of population reduction noted above. Pathogens may also play an important part in the more gradual type of decline, but this point remains to be clarified.


1963 ◽  
Vol 95 (4) ◽  
pp. 337-345 ◽  
Author(s):  
Robert W. Campbell

AbstractFour ichneumonid species, Itoplectis conquisitor (Say), Pimpla pedalis Cress., Theronia atalantae (Poda), and Theronia hilaris (Say), were seen attacking the gypsy moth, Porthetria dispar (L.), in the Town of Glenville, Schenectady County, New York. These species stung and killed many more host pupae than they successfully parasitized (success here being measured by the development of an ichneumonid offspring within the host). The ratio between the total number of hosts stung by ichneumonids and the number of ichneumonid offspring emerging was different for each of the three primary ichneumonids studied, ranging from 4 to 1 for T. atalantae to more than 200 to 1 for I. conquisitor.The sarcophagids associated with the gypsy moth, although apparently parasitic, are largely scavengers. Their attacks almost always follow those of ichneumonids. Since the sting by an ichneumonid kills the host but is not always discernible, the number of pupae containing sarcophagid larvae has been used to, indicate the true effects of ichneumonids on the host population.


Insects ◽  
2019 ◽  
Vol 10 (5) ◽  
pp. 133 ◽  
Author(s):  
Anna Papach ◽  
Jérémy Gonthier ◽  
Geoffrey R. Williams ◽  
Peter Neumann

The sex ratio of sexually reproducing animal species tends to be 1:1, which is known as Fisher’s principle. However, differential mortality and intraspecific competition during pupation can result in a biased adult sex ratio in insects. The female-biased sex ratio of small hive beetles (SHBs) is known from both laboratory and field studies, but the underlying reasons are not well understood. Here, we used laboratory mass and individual pupation to test if differential mortality between sexes and/or intraspecific interactions can explain this sex ratio. The data show a significant female-biased adult sex ratio in both mass and individual rearing, even when assuming that all dead individuals were males. Our results therefore suggest that neither differential mortality during pupation nor intraspecific interactions are likely to explain the female-biased sex ratio of freshly emerged adult SHBs. We regard it as more likely that either competition during the larval feeding stage or genetic mechanisms are involved. In addition, we compared our data with previously published data on the sex ratio of both freshly emerged and field-collected SHBs to investigate possible gender differences in adult longevity. The data show a significantly greater female bias in the sex ratio upon emergence, compared to field-collected SHBs, suggesting that adult females have a shorter longevity.


1987 ◽  
Vol 65 (5) ◽  
pp. 1284-1286 ◽  
Author(s):  
T. Andrew Hurly

A 3-year study of a red squirrel population revealed that the adult sex ratio was biased towards males. There is no evidence that the skewed sex ratio was prejudiced by sampling biases due to sexual differences in mobility, observability, trappability, or habitat use. The tertiary juvenile sex ratio was even and therefore not the cause of the biased adult sex ratio. The data suggest that the skewed sex ratio may be the result of differential mortality. This is consistent with other reports of higher female than male mortality in red squirrels.


1985 ◽  
Vol 117 (5) ◽  
pp. 535-539 ◽  
Author(s):  
Yves Mauffette ◽  
Luc Jobin

AbstractThe numbers of larvae and pupae of the gypsy moth, Lymantria dispar L., were monitored in southwestern Quebec from June through August 1980 at 13 sites. In 10 sites, the proportion of male pupae was significantly different from an expected proportion of 0.5. Linear-regression analyses of the proportion of male pupae on larval density showed a significant increase in the number of male pupae with increasing larval density. Changes in the sex ratio could be an important indicator of the dynamic state of a population, and should be considered in modeling the population dynamics of gypsy moth.


2019 ◽  
Vol 116 (25) ◽  
pp. 12373-12382 ◽  
Author(s):  
Peter R. Grant ◽  
B. Rosemary Grant

The adult sex ratio (ASR) is an important property of populations. Comparative phylogenetic analyses have shown that unequal sex ratios are associated with the frequency of changing mates, extrapair mating (EPM), mating system and parental care, sex-specific survival, and population dynamics. Comparative demographic analyses are needed to validate the inferences, and to identify the causes and consequences of sex ratio inequalities in changing environments. We tested expected consequences of biased sex ratios in two species of Darwin’s finches in the Galápagos, where annual variation in rainfall, food supply, and survival is pronounced. Environmental perturbations cause sex ratios to become strongly male-biased, and when this happens, females have increased opportunities to choose high-quality males. The choice of a mate is influenced by early experience of parental morphology (sexual imprinting), and since morphological traits are highly heritable, mate choice is expressed as a positive correlation between mates. The expected assortative mating was demonstrated when theGeospiza scandenspopulation was strongly male-biased, and not present in the contemporaryGeospiza fortispopulation with an equal sex ratio. Initial effects of parental imprinting were subsequently overridden by other factors when females changed mates, some repeatedly. Females of both species were more frequently polyandrous in male-biased populations, and fledged more offspring by changing mates. The ASR ratio indirectly affected the frequency of EPM (and hybridization), but this did not lead to social mate choice. The study provides a strong demonstration of how mating patterns change when environmental fluctuations lead to altered sex ratios through differential mortality.


1984 ◽  
Vol 98 (2) ◽  
pp. 98-109 ◽  
Author(s):  
J. Bruyn

AbstractFrom 1911 to 1961 Félix Chrétien, secretary to François de Dinteville II, Bishop of Auxerre in Burgundy, and from 1542 onwards a canon in that town, was thought to be the author of three remarkable paintings. Two of these were mentioned by an 18th-century local historian as passing for his work: a tripych dated 1535 on the central panel with scenes from the legend of St. Eugenia, which is now in the parish church at Varzy (Figs. 1-3, cf. Note 10), and a panel dated 1550 with the Martyrdom of St. Stephen in the ambulatory of Auxerre Cathedral. To these was added a third work, a panel dated 1537 with Moses and Aaron before Pharaoh, which is now in New York (Figs. 4-5, cf. Notes I and 3). All three works contain a portrait of François de Dinteville, who is accompanied in the Varzy triptych and the New York panel (where he figures as Aaron) by other portrait figures. In the last-named picture these include his brothers) one of whom , Jean de Dinteville, is well-known as the man who commissioned Holbein's Ambassadors in 1533. Both the Holbein and Moses and Aaron remained in the family's possession until 1787. In order to account for the striking affinity between the style of this artist and that of Netherlandish Renaissance painters, Jan van Scorel in particular, Anthony Blunt posited a common debt to Italy, assuming that the painter accompanied François de Dinteville on a mission to Rome in 1531-3 (Note 4). Charles Sterling) on the other hand, thought of Netherlandish influence on him (Note 5). In 1961 Jacques Thuillier not only stressed the Northern features in the artist's style, especially in his portraits and landscape, but also deciphered Dutch words in the text on a tablet depicted in the Varzy triptych (Fig. I) . He concluded that the artist was a Northerner himself and could not possibly have been identical with Félix Chrétien (Note 7). Thuillier's conclusion is borne out by the occurrence of two coats of arms on the church depicted in the Varzy triptych (Fig. 2), one of which is that of a Guild of St. Luke, the other that of the town of Haarlem. The artist obviously wanted it to be known that he was a master in the Haarlem guild. Unfortunately, the Haarlem guild archives provide no definite clue as to his identity. He may conceivably have been Bartholomeus Pons, a painter from Haarlem, who appears to have visited Rome and departed again before 22 June 15 18, when the Cardinal of S. Maria in Aracoeli addressed a letter of indulgence to him (without calling him a master) care of a master at 'Tornis'-possibly Tournus in Burgundy (Note 11). The name of Bartholomeus Pons is further to be found in a list of masters in the Haarlem guild (which starts in 1502, but gives no further dates, Note 12), while one Bartholomeus received a commission for painting two altarpiece wings and a predella for Egmond Abbey in 1523 - 4 (Note 13). An identification of the so-called Félix Chrétien with Batholomeus Pons must remain hypothetical, though there are a number of correspondences between the reconstructed career of the one and the fragmentary biography of the other. The painter's work seems to betray an early training in a somewhat old-fashioned Haarlem workshop, presumably around 1510. He appears to have known Raphael's work in its classical phase of about 1515 - 6 and to have been influenced mainly by the style of the cartoons for the Sistine tapestries (although later he obviously also knew the Master of the Die's engravings of the story of Psyche of about 1532, cf .Note 8). His stylistic development would seem to parallel that of Jan van Scorel, who was mainly influenced by the slightly later Raphael of the Loggie. This may explain the absence of any direct borrowings from Scorel' work. It would also mean that a more or less Renaissance style of painting was already being practised in Haarlem before Scorel's arrival there in 1527. Thuillier added to the artist's oeuvre a panel dated 1537 in Frankfurt- with the intriguing scene of wine barrels being lowered into a cellar - which seems almost too sophisticated to be attributed to the same hand as the works in Varzy and New York, although it does appear to come from the same workshop (Fig. 6, Note 21). A portrait of a man, now in the Louvre, was identified in 197 1 as a fragment of a work by the so-called Félix Chrétien himself (Fig. 8, Note 22). The Martyrdom of St. Stephen of 1550 was rejected by Thuillier because of its barren composition and coarse execution. Yet it seems to have too much in common with the other works to be totally separated, from them and may be taken as evidence that the workshop was still active at Auxerre in 1550.


1991 ◽  
Vol 69 (1) ◽  
pp. 208-212 ◽  
Author(s):  
Dan L. Johnson ◽  
Heather C. Proctor

The effect of predator presence on the adult sex ratio of a spider mite (Panonychus ulmi) was examined in a field experiment. Phytoseiid predators (chiefly Typhlodromus occidentalis) were removed from 32 trees harboring P. ulmi populations, and allowed to remain at natural levels on 32 other trees. Both total population density and proportion of males in the prey population were significantly higher in predator-free trees. Mechanisms that could explain the increase in the proportion of males are examined. The most probable is that greater male activity results in a higher encounter rate between predator and prey, and that subsequent higher male mortality when predators are present exaggerates the female-biased sex ratio. The theoretical effects of sex-biased predation on diplo-diploid and haplo-diploid organisms are discussed.


Sign in / Sign up

Export Citation Format

Share Document