Female Development Time Research Articles

Aspects of the Biology ofHyssopus pallidus(Hymenoptera: Eulophidae), a Parasitoid of the Codling Moth (Lepidoptera: Olethreutidae)

Hyssopus pallidus (Askew) is a gregarious ectoparasitoid that attacks 2nd-instar to prepupal codling moth. Host attack includes initial probing, host paralysis, oviposition from 2 to 30 eggs per host, nondestructive host feeding, and brood guarding. The development rate of the immature stages increased with temperature, with a life cycle minimum threshold of 10°C and a maximum threshold between 30–35°C. Female development time from oviposition to adult emergence decreased from 39 d at 15°C to 12 d at 30°C. Female longevity decreased from 115 d at 15°C to 40 d at 30°C, and was significantly increased by provision of honey, but not by host feeding. Lifetime fecundity was estimated to be 172 eggs, with a female-biased progeny sex ratio of 0.58 males and 13.02 females per host. The presence of a 1st female guarding her brood did not prevent or influence the level of superparasitism by a 2nd female; experienced females were less likely to superparasitize than naïve females, and superparasitism was most frequent among broods 24 h old. The host specificity of H. pallidus was tested using no-choice tests with 5 common orchard Microlepidoptera. It successfully attacked and developed on 100% of codling moth larvae and 60% of orange tortrix larvae. It paralyzed but did not oviposit on 20% of Pandemis pyrusana Kearfott larvae, and it did not attack obliquebanded leafroller or navel orangeworm.

Role of habitat components on the dynamics of Aedes albopictus (Diptera: Culicidae) from New Orleans.

Monthly sampling of tire pile populations of Aedes albopictus (Skuse) in Orleans Parish, New Orleans, LA, was done in 1995 to determine prevalence of ascogregarine parasites and changes in wing length. Prevalence of Ascogregarina taiwanensis (Lien & Levine) infection was 100% in midsummer and decreased in the fall and spring (60-70%). Wing lengths were longest in the spring and fall and shortest in midsummer. We evaluated the effect of A. taiwanensis infections under high and deficient levels of leaf litter nutrients on mortality, development time, wing length, and reproductive potential of a New Orleans strain of Ae. albopictus. Parasitism and deficient nutrients caused a 35% increase in the rate of larval mortality and significantly extended the development time of females. Parasitized adults were 5% smaller and produced 23% fewer eggs than unparasitized siblings. In addition, abnormal Malpighian tubule morphology and melanization of ascogregarines were seen in adults from nutrient-deficient microcosms. We conclude that ascogregarine infections affect the dynamics of Ae. albopictus by increasing the mortality of immature stages when nutrients supplies are scarce, and by decreasing the reproductive capacity of females under high nutrient conditions.

Genetic Variation in Performance Traits and the Potential for Host Shifts in Enchenopa Treehoppers (Homoptera: Membracidae)

Host plant shifts by phytophagous insects are often hypothesized as means through which new species could genetically differentiate. For genetic divergence to occur between populations on original and novel hosts, the colonizing population must possess genetic variation in performance traits allowing use of and selection by the new host. To test for the existence of genetic variation in Enchenopa treehoppers for the use of novel host plants in the genus Viburnum , we performed a 4-way full sib analysis. Related insects were exposed to 4 different plant species in greenhouse and field settings: the original host plant and 3 novel host species. We estimated genetic variation in performance traits of male and female longevity, and female fecundity and calculated fitness values, nymphal survival, and male and female developmental time to adult eclosion. We found significant genetic variation in traits influencing both survival and reproduction. There were significant interactions between genotype and host, indicating some genotypes are more adept than others at using new hosts. We conclude that sufficient genetic variation exists in this population to facilitate successful shifts to these new hosts.

Genetic variation and covariation among life history traits in populations of Acanthoscelides obtectus maintained on different hosts

AbstractWe explored the extent to which two populations of Acanthoscelides obtectus (Coleoptera: Bruchidae), maintained in the laboratory for about 60 generations on common bean (Phaseolus vulgaris) and chickpea (Cicer arietinum) seeds, differ genetically in life history traits. Using a half‐sib breeding design, we screened for genetic variation in oviposition preference for two hosts within both populations, and examined whether this variation is correlated with weevil pre‐adult (egg‐to‐adult viability and egg‐to‐adult developmental time) and adult (female fecundity and longevity) fitness components on these two hosts. Significant differences between the Phaseolus and Cicer population were detected in viability, developmental time and oviposition preference, but not in female fecundity and longevity. The absence of a significant population × host interaction in all traits, except for developmental time in males, indicates that the Cicer population has not attained the status of ‘host race’. The estimated narrow‐sense heritabilities within population within host plant were in the low‐to‐moderate level (range: 1%–79%), with an overall average of about 24%. Within the population maintained on the chickpeas we detected significant genetic correlations between female developmental time on chickpea seeds and preference for chickpeas. In the population maintained on the primary host of this weevil species (the ‘Phaseolus’ population) we found no significant preference/performance genetic correlations. Data are also presented on the genetic correlations of preference and performance across host seeds within both populations. These correlations are found to be positive for all traits in both populations, indicating the absence of trade‐offs in either performance or behavioural response that might impose selection for host specialization within populations.

HERITABILITY OF DEVELOPMENT TIME AND PROTANDRY IN THE PITCHER-PLANT MOSQUITO,WYEOMYIA SMITHII

Models of protandry (1) assume implicitly or explicitly that independent evolution of male and female preadult development times is possible and (2) assume or assert that protandry should increase in populations that are univoltine or at least composed of discrete, nonoverlapping generations. Herein we examine these assumptions in the pitcher-plant mosquito, Wyeomyia smithii. Heritability and additive genetic variance of development time are higher in female than in male W. smithii. Protandry is higher in lines selected for slow development than in lines selected for fast development or in unselected control lines. Protandry is therefore capable of evolving. Contrary to predictions based on sexual selection, southern populations with multiple, overlapping generations are just as protandrous as northern bi- and univoltine populations with discrete generations. Voltinism and developmental synchrony of the population do not appear to have been major selective factors in the evolution of protandry in W. smithii. We propose that protandry can be maintained by natural selection in multivoltine populations with overlapping generations as a consequence of sexually dimorphic fitness criteria. Selection should minimize development time in males but maximize growth rate in females. In W. smithii, females achieve higher growth rate than males but also harbor greater genetic variation for development time, indicating that selection has, indeed, minimized development time to a greater extent in males than in females. We conclude that if both natural and sexual selection are involved in the maintenance of protandry in populations of W. smithii, then their relative importance changes with the degree of generation overlap.

Sex Allocation and Sexual Asymmetries in Intra-Brood Competition in the Parasitic Wasp Bracon hebetor

1. Bracon hebetor is a gregarious parasitoid with a female-biased sex ratio. While female-biased sex ratios are often indicative of local mate competition (LMC), B. hebetor outbreeds, making LMC an unlikely explanation for biased sex ratios in this species. In this study we examined an alternative hypothesis that may explain female-biased sex ratios: competitive asymmetries between larval sons and daughters. 2. We measured two types of competitive asymmetries: asymmetric density responses (differential responses to clutch size), and asymmetric composition responses (responses to change in clutch sex ratio). We measured competitive asymmetries in terms of their effects on body size, development time, survivorship, longevity, and daily and lifetime fecundity or mating ability. 3. Males and females emerged as smaller adults, developed more quickly and experienced higher rates of larval mortality when they developed in larger clutches. The effect of clutch size on body size and survivorship was similar for males and females. Increasing clutch size decreased male larval development time more than female development time, although the effect was marginal. 4. Male and female body sizes increased as within-clutch sex ratios became more male-biased, indicating that females, not males, are stronger competitors. This should lead to male-biased sex ratios, rather than the female-biased sex ratios that exist in B. hebetor. Sex ratio had no influence on developmental time or survivorship of either sex. 5. Larger males and females lived longer than smaller individuals, whether they fed on hosts or honey. Larger females had higher daily and lifetime fecundities than smaller females. Larger males copulated with more females and sired more daughters both per day and per lifetime than did smaller males. These body size effects were only detectable when hosts were abundant. At low host densities, differences between large and small wasps were absent. 6. Although we detected asymmetric composition responses in terms of body size, the effects were slight. Therefore, we conclude that competitive asymmetries are unlikely to have important effects on male and female fitness or on the sex allocation decisions of B. hebetor.

The Biology of Encarsia tricolor: An Autoparasitoid of Whitefly

Abstract Encarsia tricolor Forster (Hym.: Aphelinidae) is an autoparasitoid of a number of whitefly pest species. Females develop as primary endoparasitoids, whereas males develop hyperparasitically in other whitefly endoparasitoids including conspecific females. Under a constant regime of 25°C and 16:8 h L:D, the biology of E. tricolor was investigated using the Cabbage whitefly, Aleyrodes proletella, as host. The following results were obtained. (1) A significant positive linear correlation was detected between size and longevity for both sexes, given a honey diet. Mean (±SE) longevity was 16.9 ± 0.62 days for females and 13.8 ± 0.66 days for males. Females were significantly larger than males. (2) Female E. tricolor could develop in all host instars. Development times were slowest in first instar nymphs (22.3 ± 0.34 days) and fastest in fourth instar nymphs (18.7 ± 0.25 days). Female development times were not overtly variable. (3) Male E. tricolor could hyperparasitize all stages of conspecific female larvae and pupae offered. When parasitizing larvae, male development times were longer, indicating that male development is delayed until the host approaches pupation. (4) Mean (±SE) lifetime fecundity of E. tricolor laying female eggs was 85.36 ± 13.85 at a mean rate of 7.31 ± 0.27 eggs/female/day. (5) In a study of sex ratio dynamics in the parasitoid culture, emergent sex ratios were a function of the period of parasitism. The emergent sex ratio (percentage male) from individual leaves increased from 44% after 2 weeks in the culture to 76% after 4 weeks. A concurrent increase in the overall percentage parasitism was also recorded: 23 ± 3.4% at 2 weeks to 87 ± 4.1% at 4 weeks. (6) Observations on oviposition behavior indicated a clear preference to exploit late instar nymphs for female production. All whitefly instars were used for host feeding. Oviposition times for male eggs (in conspecific pupae) were significantly greater than for female eggs (in late instar whitefly nymphs).

Gene–environment interaction for body size and larval density in Drosophila melanogaster: an investigation of effects on development time, thorax length and adult sex ratio

We measured the effect of larval density on thorax length, development time, sex ratio and a measure of total fitness, using strains of Drosophila melanogaster artificially selected for increased thorax length, control lines otherwise cultured in an identical way, and the base stock from which the lines had been derived. We used the addition experimental design (Mather & Caligari, 1981). No genotype-environment interaction was observed when comparing the reduction in thorax length of 'large' and 'control' lines with increasing larval density for any culture series, i.e. rank ordering of genotypes and additive genetic variances remained the same in all the environments tested. In contrast, the reduction in thorax length for the base stock as density increased was proportionally smaller than that of the 'large' and 'control' lines. Development time increased more rapidly with larval density in the 'large' lines than in the 'controls' or base stock. Sex ratio was unaffected by larval density but thorax length and the development time of females were more affected than those of males by increasing larval density. The estimate of total fitness showed clear evidence of gene-environment interaction for the effect of body size on fitness, with genetically large individuals at an increasing disadvantage with increasing larval density.

Differences in life history traits between isofemale lines of the aphid parasitoidAphelinus abdominalis(Hymenoptera: Aphelinidae)

AbstractSix isofemale lines of the aphid parasitoidAphelinus abdominalis(Dalman) were compared for life history traits related to parasitism of three cereal aphid species. The lines differed most in the number of hosts parasitized in 24 h and the developmental times of females and males. Cluster and discriminant analysis showed that these differences were pronounced between line I, line II and lines III-VI, but not between lines III, IV, V and VI. Cross-breeding experiments revealed reproductive barriers between the lines which proved to differ most in life history traits, indicating the possible existence of morphologically similar species. Given the variability in life history traits between lines ofA. abdominalisrecorded in this study, we suggest a careful selection of candidate strains for biological control will be rewarding.

Effect of Temperature on Life History Characteristics of Anisopteromalus calandrae (Hymenoptera: Pteromalidae) Parasitizing Maize Weevil Larvae in Corn Kernels

The second generation of Anisopteromalus calandrae (Howard) collected from commercial stored com in South Carolina was reared at constant temperatures of 20, 25,30, and 35°C at 63% RH and a 12: 12 (L:D) photoperiod. Hosts were medium to large larvae of Sitophilus zeamais Motschulsky reared on corn (21–23 d old at 25°C, 63% RH). Daily production of viable progeny, sex ratio, adult female survivorship, and development time were measured to calculate net reproductive rate ( R o), generation time ( T ), intrinsic rate of increase ( R m), and female adult life expectancy. Female longevity was greatest at 20°C (14.5 d median) and shortest at 30 and 35°C (6 d). Median female development time ranged from 44 d at 20°C to 10 d at 35°C. Mean number of progeny produced per female over her lifetime increased from 10.4 at 20°C to 42.6 at 35°C. Progeny sex ratio was much lower at 20°C (33% female) than at the other temperatures (63–71% female). Intrinsic rate of increase was lowest at 20°C (0.028 female per female per day) and greatest at 35°C (0.250), R o increased from 4.5 female per female at 20°C to 27.7 at 35°C, and T decreased from 53.5 to 13.3 d.

Labeling a Parasitic Wasp, Microplitis croceipes (Hymenoptera: Braconidae), with Trace Elements for Mark—Recapture Studies

Microplitis croceipes (Cresson), a parasitoid of larvae of Heliothis spp., was labeled by rearing it in host larvae that were fed diet containing 1,000-2,000 parts per million of one or more of four trace elements: cesium (Cs), dysprosium (Dy), rubidium (Rb), or strontium (Sr). Atomic absorption spectrophotometry was used for the analysis of the labels. Cs and Dy concentrations in Cs-labeled and Dy-labeled parasitoids overlapped those found in parasitoids reared on unlabeled diet. Although the amounts of Rb and Sr in labeled parasitoids declined after they emerged as adults and ceased to be exposed to a trace element source, parasitoids labeled with these elements were distinguishable from field-collected, unlabeled insects up to 20 d after adults emerged. Although development time of males and females and adult longevity of females differed between unlabeled and labeled parasitoids, the differences were small and the direction of the differences reversed between experiments, suggesting that the trace elements had little effect on development time or adult longevity.

Nutrient deficiencies and the gypsy moth, Lymantria dispar: Effects on larval performance and detoxication enzyme activities

We investigated the consequences of specific nutrient deficiencies for growth performance, food processing efficiencies and detoxication enzyme activities in larvae of the gypsy moth, Lymantria dispar. Larvae were reared on one of four artificial diets, including a low wheat-germ control diet, and protein-, mineral- and vitamin-deficient diets. Growth of fourth instars was reduced on each nutrient-deficient diet; reductions were attributable to decreased efficiencies of conversion of digested food. Larvae on the low protein diet exhibited compensatory feeding responses, but not great enough to offset the reduction in protein intake. The low protein and low mineral diets prolonged development time of females, and reduced pupal weights of males and females. All larvae fed the low vitamin diet succumbed to a nuclear polyhedrosis virus late in the fifth larval stadium. We observed few significant effects and no clear-cut patterns of response of detoxication enzymes to nutrient limitation. Polysubstrate monooxygenase and glutathione transferase activities were unaffected. Soluble esterase and carbonyl reductase activities tended to increase in response to protein deficiency, but decrease in response to vitamin deficiency. Phytophagous insects evolutionarily adapted to feeding on nutrient-poor but allelochemical-rich host plants may have evolved biochemical/physiological mechanisms that serve to maintain effective enzyme function in the context of nutrient deficiency.

Within and Among Site Variability in Gypsy Moth (Lepidoptera: Lymantriidae) Performance on Five Tree Species

Comparisons of the suitability of different tree species as food for the gypsy moth, Lymantria dispar (L.), have usually been based on measurements of larval growth on foliage samples taken from few tree individuals at single field sites. By rearing gypsy moth larvae on five tree species (three preferred [all oaks] and two marginal) at sites located in three physiographic regions, we tested whether differences in suitability among tree species can vary from location to location. Relative suitabilities did not vary among locations for weight of female pupae or development time of male larvae, but there were some differences for weight of male pupae and development time of female larvae. These tree species × location interactions, however, accounted for little of the overall variability in gypsy moth pupal weight and development time on the three oak species. The largest sources of variation, aside from sex, were differences among larvae on the same tree and differences among trees of the same species. Some factors that were controlled for in this study, such as tree size (trunk diameter was positively correlated with weights of male and female pupae), phenology, extent of defoliation, and genetic differences among gypsy moth populations, may contribute to differences in the relative suitability of tree species among naturally occurring sites of infestation. Nevertheless, results of this experiment suggest that in studies of relative suitability, sampling replicate trees within species is more crucial than including multiple study sites.

The Significance of Leaf Detritus to Mosquito (Diptera: Culicidae) Productivity from Treeholes

Relationship between leaf detritus and productivity of Aedes triseriatus (Say) from beech treeholes was studied. Leaf mass in treeholes was positively correlated with area of treehole entrance. Leaf packs in treeholes lost ca. 69% of their mass during the summer season. In the first experiment lasting 18 wk, there was no difference in number of mosquitoes emerged, average individual mass, development time, or total mass of males or females from treeholes without leaves or treeholes with leaves. Individual mosquitoes were not generally smaller in size with increasing date of emergence. Inorganic nutrient (nitrite, nitrate, phosphate, sulfate, and ammonia) and dissolved organic carbon concentrations in treehole water varied seasonally with rainfall and other factors but did not differ between groups of treeholes with or without leaves. Bacterial concentrations in treehole water were higher in nine treeholes before than after a rainfall, ranging overall from 1.92 × 106 to 54.70 × 106 cells per ml. In a second experiment lasting about seven weeks, there was no difference in larval mass between treeholes with leaves and those without leaves. Behavioral observations showed that larvae filtered treehole water and browsed tree bark and leaves. Overall, our results suggest that leaves are probably only one of many food resources for mosquito larvae in treeholes; bacteria in treehole water may be more important as food than microbiota attached to leaves.

Development Rate and Survivorship of Immature Urolepis rufipes (Hymenoptera: Pteromalidae), a Parasitoid of Pupal House Flies

Urolepis rufipes (Ashmead), a parasitoid of house flies, Musca domestica L., recently discovered in New York dairies, was reared at 15, 20, 25, 30, and 34°C to measure development rate and survivorship of immatures. Little development occurred at 15°C, and only a few females successfully emerged at 34°C. Female development time from egg to adult was 29, 13, 10, and 11 days at 20, 25, 30, and 34°C, respectively. Males emerged 1–3 days sooner than females, depending on temperature. Percentage of emergence was significantly affected by temperature, and females were significantly more successful in emerging from host puparia than males. Survival rate of immature progeny did not differ significantly with age of the mother. U. rufipes has a faster development rate than most other house fly parasitoids studied to date, making it an attractive biological control agent.

GENETIC VARIATION IN PLANT-INSECT ASSOCIATIONS: SURVIVAL OF LEPTINOTARSA DECEMLINEATA POPULATIONS ON SOLANUM CAROLINENSE.

Populations of the Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae), from the east coast of the United States differ in their ability to survive on a wild host, Solanum carolinense (Solanaceae), but not on their most important cultivated host, Solanum tuberosum. On the wild host, the North Carolina population survived best, while populations from Virginia, New Jersey, and Connecticut exhibited uniformly low survival. Formal genetic studies of populations from Connecticut and North Carolina demonstrated heritable variation in the ability to survive on S. carolinense both between and within populations; the North Carolina population had the higher heritability for this trait. Overall, there was no genetic variation between populations or within the North Carolina population for survival on S. tuberosum, but such variation existed within the Connecticut population. Hybrids and backcrosses between these two lines all survived at intermediate levels, although survivorship did not appear to be inherited additively. Differences in survival were greater than differences in adult weight at emergence and development time of the survivors. Leptinotarsa decemlineata was first reported from North Carolina less than 100 years ago. The rapid expansion of L. decemlineata's host range in North Carolina is attributed to the poor synchrony between the insect and S. tuberosum compared to more northerly locations. In contrast to the prediction of a strong negative correlation in fitness on different host species, the ability of L. decemlineata to survive on S. carolinense was not correlated with that on S. tuberosum. Adult weight and female development time were significantly positively correlated across hosts. Our results are in accord with most previous studies in which strong negative correlations in fitness of specialized phytophagous insects feeding on different hosts were expected, sought, but not found.

Experimental test of the pupation window model for development of detritivorous insects

Cohort size and food availability to larval detritivores are linked to pupal mass, and hence to adult fitness, by the pupation window model. Previous tests of this model have employed artificial food. This paper derives a version of the model that incorporates the dynamics of natural detritus. Tests of the model using cohorts of Aedes triseriatus Say led to successful predictions of numbers of pupae, female pupal mass, and female development time. However, it is recommended that model parameters be estimated separately for different types of leaf litter.

Competition Within and Between Hatching Chorots of a Treehole Mosquito

Aspects of population growth rates are examined for cohorts of the treeholes mosquito Aedes triseriatus, reared in field containers under different conditions of larval density, concentration of natural treehole fluid, and in the presence or absence of a late—hatching cohort of larvae. Density and fluid concentration produced similar and independent significant competitive effects on each measure of cohort success, including female mass, development time, and survival to the adult stage, as well as on a composite index of performance. The sensitivity of first—cohort development time to high density and dilute fluid was reduced by the presence of the second cohort, and first—cohort survivorship responses to fluid concentration and density suggest an enhanced performance in dilute medium and intermediate density due to the addition of the second cohort. A composite index did not detect these complex interactions of experimental factors, suggesting that overall population growth rates for the first cohort respond to density and food in a very simple manner. The second cohort experienced total mortality in the presence of high first—cohort density, dilute medium, or the incidental oviposition of another treehole mosquito, Anopheles barberi, and never matched the success of the first cohort, even under conditions of low density and concentrated fluid.

A Temperature-Dependent Model for Fall Armyworm Development1,2

The influence of temperature on egg-to-adult developmental times and rates of the fall armyworm, Spodoptera frugiperda (J. E. Smith), was studied in the laboratory at a variety of constant and variable temperatures. Mean total developmental time ranged from 66.6 days (15.6°C) to 18.4 days (35.0°C). Male and female development times were not significantly different. Means and standard deviations of fall armyworm developmental rates (= times−1) were inputs into a previously derived absolute reaction rate model designed to generate a set of kinetic constants usable in predicting developmental times. The distribution of cohort developmental times was compared to predictions from an existing stochastic cohort model and was found to be in reasonable agreement at all temperatures tested.