Effects of host species, stage and size on the sex ratio and clutch size of the parasitoid, Dibrachys boarmiae (Walker, 1863) (Hymenoptera: Pteromalidae)

Effects of host species, stage and size on clutch size and sex ratio of the gregarious, idiobiont ectoparasitoid Dibrachys boarmiae were investigated at 25±2°C and 70±5% relative humidity. The greater wax moth, Galleria mellonella, small wax moth, Achroia grisella, and early stage solitary larvae of the endoparasitoid, Apanteles galleriae, were used as hosts. Clutch size was greatest from prepupae of the largest host, Galleria mellonella, with a mean of 40.07 offspring per host versus 14.73 and 2.93 for Achroia grisella and Apanteles galleriae, respectively. The mean clutch size from pupae was lower than from prepupae, being 17.27, 10.73 and 2.89 for Galleria mellonella, Achroia grisella and Apanteles galleriae, respectively. Within each host species and stage, heavier hosts resulted in larger clutches. The sex ratio of offspring (proportion of male) was approximately 0.20, with only minor differences among host species, stages and sizes.     

Age-specific survival and fecundity and their effects on the intrinsic rate of increase of Aphelinus gossypii (Hym., Aphelinidae), a parasitoid of Aphis gossypii (Hom., Aphididae)

Abstract: The age-specific survival and fecundity of female adults of the aphidophagous parasitoid, Aphelinus gossypii Timberlake (Hym., Aphelinidae), were determined at a host density of 50 Aphis gossypii Glover (Hom., Aphididae) per leaf of Ageratum houstonianum Mill each day at 25°C. The age-specific mummy production, emergence rate and sex ratio of progeny were calculated. The implication of these results in terms of potential population growth of A. gossypii and related species is discussed. The age-specific survival curve ( l _x ) of females exhibited a Type I pattern, which resulted in little difference between Σ m _x and Σ l _x   m _x . The l _x curve of males exhibited a Type II pattern, and their survival time was much shorter than that of females. Each mated female produced on average 598.9 ± 64.0 aphid mummies, and preyed on 87.9±6.2 aphids. Most of the biological performance parameters were not different significantly between mated and virgin females. The highly female-biased sex ratio of offspring produced by mated females soon after their emergence resulted in a high fecundity rate ( m _x ) during the early reproductive period. Therefore, although the sex ratio of progeny was male-biased during the entire reproductive period, the intrinsic rate of increase estimated using age-specific sex ratios was larger than that estimated using a constant sex ratio of 0.5. These results indicate that the high survival and the adaptation of producing mostly female offspring during the early reproductive period contribute much to the population increase potential of this parasitoid.     

Host-size-dependent feeding behaviour and progeny sex ratio of Anisopteromalus calandrae (Hym., Pteromalidae)

Host-size related feeding and oviposition behaviour, and allocation of progeny sex by Anisopteromalus calandrae (Howard) were tested on Sitophilus oryzae L. The parasitoid showed a host-size-dependent partition of feeding and oviposition behaviour, preferring small hosts for feeding, but large hosts for oviposition. Neither the mutual interference nor the host density showed any effect on the behaviour of the parasitoid. Allocation of progeny sex by the female parasitoid appeared to be based more likely on absolute than on relative host size encountered. A model for the progeny sex ratio was constructed based on: (1) ovipositional preference of the parasitoid on large hosts; (2) feeding preferentially on small hosts; and (3) host-size-related regulation of progeny sex ratio. The progeny sex ratio of the parasitoid predicted by the model was in close agreement with the observed value.     

Mass-rearing biology of Fopius vandenboschi (Hym., Braconidae)

Abstract:   Basic biological information concerning the reproductive activities of Fopius ( Biosteres ) vandenboschi (Fullaway) (Hym., Braconidae, Opiinae) were determined to facilitate insectary mass production. Mean (±SE) progeny production per generation (yield) of 200 ♀♀ F. vandenboschi was 6835.8 ± 433.2 and 3755.8 ± 112.4 parasitoids, with 24-h exposure to second instar Bactrocera dorsalis (Hendel), and Ceratitis capitata (Wiedemann), respectively. Ceratitis capitata as a factitious host was more sensitive to parasitism, producing a significantly higher percentage of uneclosed host puparia frequently containing parasitoid cadavers (22.5 ± 0.8%), than B. dorsalis (3.4 ± 0.2%). The overall mean production of female offspring was ≥50%♀♀ in both host species. Unlike several other opiine parasitoids, young (5-day-old) females of F. vandenboschi produced low proportion of daughters (26–37%♀♀) and significantly shifted production to female-biased offspring (53–71%♀♀) at older age intervals (16–30 days). Based on the parasitoid yield data with a 24-h exposure period to second instar host larvae of B. dorsalis , about 150 cage replicates (of 200 ♀♀ each) may be sufficient to mass produce about 1 million parasitoids of F. vandenboschi during the reproductive period of 5–30 days, with an average of 56% female offspring. A short oviposition exposure period of 6 h was not optimal for mass production of F. vandenboschi . Total yield at 6 h exposure was one-fifth the production at 24-h exposure, using B. dorsalis hosts.     

Impact of mating on Anagyrus kamali Moursi (Hym., Encyrtidae) lifetime fecundity, reproductive longevity, progeny emergence and sex ratio

Abstract: The solitary endoparasitoid Anagyrus kamali Moursi (Hym., Encyrtidae) and the Hibiscus mealybug Maconellicoccus hirsutus Green (Hom., Pseudococcidae), were used as a parasite/host model to test the effect of mating on several fitness parameters, i.e. longevity, lifetime fecundity, progeny emergence and sex ratio. At 27 ± 2°C, 8 h light : 16 h dark, mating significantly affected the survival of male parasitoids. Virgin males lived longer (32.2 ± 9.51 days) than mated males (23.9 ± 7.52 days). Female longevity (40.7 ± 16.3 days for virgins and 36.2 ± 10.7 days for mated females) was not affected by mating. The lifetime fecundity of female parasitoids and their oviposition period was not significantly affected by mating. However, the number of hosts parasitized was greater for mated wasps (7.54 ± 4.85 hosts parasitized/day) compared with virgin ones (5.12 ± 2.19 hosts parasitized/day). This resulted in greater progeny production from mated A. kamali females. The progeny of virgin females consisted only of males, whereas the mated ones had a more female‐biased sex ratio. The lowest sex ratio (0.41 M/F ± 0.123) was attained when females had free access to males and were multi‐mated.     

Sex ratio bias in the F1 adult progeny of African rice gall midge, Orseolia oryzivora H. and G. (Dipt., Cecidomyiidae)

Abstract:  Against the background of conflicting reports of variable sex ratio distribution in different populations of the African rice gall midge (AfRGM), Orseolia oryzivora Harris and Gagne, the number and sex ratios of F₁ adult progeny produced per female from wild and screen house populations were investigated in the screen house at 27 ± 3°C, 60–70% relative humidity and 12 : 12 h (light : dark) photoperiod. Results indicated the occurrence of a single sex-biased ratio in all the F₁ adult progeny produced per female of this pest. Regardless of the source, whether from wild or screen house population, each mated female AfRGM produced a full complement of either sex only but never both. The difference between the number of eggs laid and F₁ adult progeny that emerged per female from wild and screen house populations was not significant (P > 0.05), indicating consistency in the occurrence of this phenomenon among AfRGM populations. The reason for this could not be ascertained in this study but AfRGM eggs must be fertilized for development and eclosion to occur. No F₂ adults emerged when a cohort of emergents from the same female were allowed to re-infest susceptible seedlings, indicating absence of parthenogenesis.     

Impact of males on the progeny sex ratio of Campoletis chlorideae (Hym., Ichneumonidae), a parasitoid of Helicoverpa armigera (Hübner) (Lep., Noctuidae)

Abstract: The endoparasitoid Campoletis chlorideae and its host Helicoverpa armigera were reared in the laboratory to determine the progeny sex ratio of C. chlorideae in the presence and absence of male parasitoids. It was observed that the presence of male parasitoids affects the progeny sex ratio by decreasing the number of females in the offspring population, i.e. a significant increase in the proportion of males was observed in united sexes. Therefore, while constructing the life table of the parasitoid, the effect of presence of male parasitoids, should be considered together with other factors, which decreases the efficiency of the parasitoid.     

Daily progeny production and thermal influence on development and adult longevity of the leafminer parasitoid, Gronotoma micromorpha (Hym., Eucoilidae)

Abstract:  To evaluate the potential of the parasitoid Gronotoma micromorpha (Perkins) as a biological control agent for the serpentine leafminer Liriomyza trifolii (Burgess) in greenhouses, we determined daily progeny production and thermal influence on both total development (oviposition to adult emergence) and adult longevity of this wasp in the laboratory in the host L. trifolii . The mean total number of progeny produced was 75.6 per female at 25°C under a 15-h light/9-h dark (15L : 9D) photoregime. The developmental rate of G. micromorpha significantly correlated with constant temperature between 18 and 30°C. The lower thermal threshold and thermal constant for total development of this wasp were 11.7°C and 333.3 heat degree-days, respectively. The results indicate that adult female G. micromorpha do not oviposit at 15°C and that the lower threshold for oviposition is approximately 18°C. In heated greenhouses in Japan, leafminers and their parasitoids are exposed to both high temperatures and a short photoregime from late autumn to winter, but these conditions (25°C, 10L : 14D) did not significantly affect the total development of G. micromorpha . When wasps were not exposed to hosts, the mean adult longevity at 15 or 20°C was significantly longer than that at 25°C. When wasps were allowed to oviposit into hosts at 25°C, the mean adult longevity was significantly longer than when wasps were not exposed to hosts. As adult female G. micromorpha do not feed on hosts and are pro-ovigenic, suppression of oviposition probably decreased adult longevity. The biological traits of G. micromorpha elucidated by this and previous studies indicate that this wasp is suitable as a biological control agent for L. trifolii in greenhouses.     

Interspecific competition between Cephalonomia stephanoderis and Prorops nasuta (Hym.,Bethylidae), parasitoids of the coffee berry borer, Hypothenemus hampei (Col., Scolytidae)

The competition between Cephalonomia stephanoderis and Prorops nasuta was studied in the laboratory, using coffee fruits infested with the host of these parasitoids, the coffee berry borer Hypothenemus hampei . Experiments were performed under different conditions, using: (a) three temperatures; (b) five densities of infested coffee fruits; and (c) introducing the parasitoids at different times. The effect of competition was determined according to the production of the progeny. When cultured together at the same time, C. stephanoderis produced in general, more progeny than P. nasuta under conditions of 29°C and alternating temperatures of 18–29°C. Nevertheless, there were significant differences at densities of 1 : 3, fruits : parasitoids ( F _0.05=8.9; d.f.=1, 12; P < 0.05) and 1 : 5 ( F _0.05=7.56; d.f.=1, 12; P < 0.05) at 29°C. Under alternating temperatures, there were differences at the same ratios as above in favour of C. stephanoderis , 1 : 3 ( F _0.05=20.08; d.f.=1, 12; P < 0.05) and 1 : 5 ( F _0.05=20.21; d.f.=1, 12; P < 0.05). Prorops nasuta was clearly more successful in all densities at 18°C. When C. stephanoderis was introduced 10 days before P. nasuta , the progeny production was markedly higher in eight from 10 densities at temperatures of 29°C and 18–29°C. Despite being introduced 10 days later, P. nasuta showed better performance at 18°C. When P. nasuta was introduced 10 days earlier than C. stephanoderis , there were significant differences in progeny production in favour of P. nasuta in 13 of 15 fruit densities under the three temperatures. Both parasitoids avoided ovipositing on previously parasitized hosts. Aggressive behaviour or interference was not observed when they were outside coffee fruits.     

Studies on the bionomics ofTrioxys (Binodoxys) indicus [Hym.: Aphidiidae]: Effect of population densities on sex ratio

The effect of different population densities ofTrioxys (Binodoxys) indicus Subba Rao & Sharma and its hostAphis craccivora Koch, on the sex ratio (female: male) of the parasitoid was observed. The sex ratio (favouring female sex) increased with increase of host density. Parasitoid contamination priciple and behavioural responses of female parasitoid in addition to environmental factors were applied to explain the results. Results clearly indicated that fewer parasitoid releases might be better at any immediate release site for the production of maximum female progeny in this species.     

Inter-larval Competition and its Subsequent Effect on Pediobius furvus (Hym.: Eulophidae) Broods for the Management of Graminaceous Stem Borers

The effects of superparasitism on the size, rate of development, progeny production, sex ratio and percentage parasitism of the parasitoid Pediobius furvus (Gah.) and the number of parasitized hosts producing mature parasitoids were investigated. High parasitoid egg densities in hosts were obtained using two host densities (1 and 2) and three arbitrary parasitoid densities (1, 2 and 5) under two exposure times (12 and 24 h). Superparasitism in P. furvus resulted in a reduction in the number of adults that matured and a reduction in the size and preponderance of male production. Dissections of the parasitized host pupae of the stem borer Chilo partellus (Swinhoe) showed no combat among developing wasps. Immature supernumeraries were eliminated by starvation and/or suffocation. The results showed that P. furvus larvae are not harmed by surplus food material in their hosts and that the female parasitoid preferred to lay more eggs into unparasitized than into parasitized host pupae.     

Evaluation of entomopathogenic nematodes for control of the beetle, Luperomorpha suturalis Chen (Col., Chrysomelidae)

Abstract: The strains Steinernema feltiae Otio and A54, Steinernema ceratophorum D43 and Steinernema carpocapsae BJ were tested for their infectivity to the larvae and pupae of beetle ( Luperomorpha suturalis Chen) at 25 ± 0.5°C and 15 ± 0.5°C in laboratory conditions. The results, based on comparison of the insect mortalities and nematode penetration rates among four nematode strains, showed that S. feltiae Otio was a potential biocontrol agent of the larvae and pupae of L. suturalis . The mortalities of the larvae and pupae exposed to S. feltiae Otio strain were 95.8 and 97.1% at 25 ± 0.5°C and 78.0 and 83.0% at 15 ± 0.5°C, respectively. The nematode penetration rates of S. feltiae Otio of the larvae and pupae were 15.6 and 19.0% at 25 ± 0.5°C, 2.6 and 6.3% at 15 ± 0.5°C, respectively. Field efficacy of S. feltiae Otio strain was examined against beetle larvae in Hebei province, northern China. The population reduction of insect larvae was 77.8 and 13.9% at doses of 30 and 15 infective juveniles (IJs)/cm² of S. feltiae Otio after 38 days of treatment and 90.2 and 92.4% after 100 days of treatment. However, the population of the insect larvae was reduced only to 15.5 and 15.7% when treated with pesticide after 38 and 100 days, respectively. The efficiency between the two nematode doses was not significantly different but it was remarkably higher than that of the pesticide after 100 days of application. The results suggest that S. feltiae Otio strain could be an alternative to pesticide for beetle control.     

Factors affecting sex ratio in rearing ofCoeloides sordidator (Hym.: Braconidae)

Five factors known to affect the sex ratio (% of males) in parasitic Hymenoptera were investigated forCoeloides sordidator, a parasitoid ofPissodes weevils. The host age, the age of ovipositing females, and the host of origin had a significant impact on the sex ratio of offspring. In contrast, the number of ovipositing females had an insignificant effect on sex ratio whereas the effect of host density could not be clearly defined. The sex ratio decreased with host age, probably because, like many other hymenopteran parasitoids, females tend to lay male eggs on small hosts and female eggs on larger hosts in order to maximize the size and fitness of their female offspring. The sex ratio also varied with the age of the mother, younger females laying more male eggs and older females more female eggs. The host of origin also had an influence on sex ratio. The strain fromPissodes castaneus was significantly more male-biased than the strain fromP. validirostris, which corroborates previous observations made on field populations     

Malathion-induced oxidative stress in a parasitoid wasp: effect on adult emergence, longevity, fecundity, and oxidative and antioxidative response of Pimpla turionellae (Hymenoptera: Ichneumonidae)

Effects of an organophosphorus insecticide, malathion, on survivorship and lipid peroxidation of the greater wax moth, Galleria mellonella (L.), pupae were investigated by rearing the newly hatched larvae on an artificial diet containing 0.01, 0.1, 1, 10, and 100 ppm of the insecticide. As bioindicators of long-term physiological stress responses, the adult emergence rate, longevity, and fecundity associated with lipid peroxidation level and antioxidant enzyme activity in the endoparasitoid Pimpla turionellae (L.) (Hymenoptera: Ichneumonidae) were determined by rearing the parasitoid on a factitious host, G. mellonella pupae treated with malathion. At 100 ppm, malathion significantly decreased pupation rate of G. mellonella larvae and the rate of adult emergence of the parasitoid from these pupae. This concentration resulted in a significant increase in the lipid peroxidation product malondialdehyde (MDA) in both the host and the parasitoid. Malathion at 1 and 10 ppm significantly increased pupation rate and lipid peroxidation level of G. mellonella pupae. The adult emergence rate of P. turionellae was significantly decreased from 63.7 to 20% by these concentrations, whereas MDA content was increased by two- and three-fold, respectively, compared with the control (45.3 +/- 3.2 nmol/ g protein). The longevity of adults was significantly extended from 52.5 +/- 5.7 to 75.7 +/- 6.3 d when the parasitoids emerged from host pupae exposed with 0.1 ppm malathion. At low concentrations (0.01 and 0.1 ppm), malathion significantly increased the number of eggs laid per female per day. However, the lowest concentration (0.01 ppm) had no significant effect on hatchability, whereas 0.1 ppm of the insecticide resulted in significant decrease in egg hatch compared with the control. A significant increase in total superoxide dismutase (SOD) activity for low concentrations of malathion (0.01-1 ppm) was found compared with the control. There was a significant positive correlation of SOD activities with adult longevity and fecundity. This study suggested that malathion-induced oxidative stress was causative factor in the deterioration of biological fitness and that increased SOD activities may have resulted in decreased oxidative damage, which retarded the rate of deteriorative physiological changes in P. turionellae in response to sublethal doses of malathion.     

Increased male sex ratio among brachypterous progeny in Melittobia femorata, a sib-mating parasitoid wasp (Hymenoptera: Eulophidae)

Abstract Melittobia are gregarious ectoparasitoid wasps that primarily attack various solitary bees and wasps. Characterized by high levels of inbreeding and an extremely female-biased sex ratio, these wasps appear to satisfy Hamilton's criteria for local mate competition. However, previous studies of sex ratio have failed to take into account an important aspect of Melittobia life history, namely that every clutch represents the combined reproductive output of the initial foundress female plus as many as 37 non-disperser short-winged daughters. Melittobia femorata Dahms is unique among the 13 species of Melittobia in that adults emerge as two temporally distinct clutches. While the overall sex ratio of the combined progeny from both clutches (0.025 ± 0.01) is typical for that for other Melittobia species (between 0.02 - 0.04 for single foundress cultures of the five other species included in this study), the sex ratio for the brachypterous first clutch of M. femorata from field-parasitized hosts averaged about 10 times greater (0.303 ± 0.10). Laboratory experiments with single foundress M. femorata cultures on the same host species ( Trypoxylon politum Say) maintained at 25°C or 30°C produced smaller first clutch sizes compared to the field-infested hosts. While the number of brachypterous first clutch daughters was similar, significantly reduced first clutch sex ratios relative to field-parasitized hosts (0.07 - 0.10) were due to significantly fewer males being produced. Possible reasons for these differences and the elevated first clutch sex ratio in this species are discussed.     

Sex Allocation by a Parasitoid Wasp (Hymenoptera: Ichneumonidae) to Different Host Species: A Question for the Mechanism of Host Size Estimation

Sex allocation by the polyphagous solitary pupal parasitoid wasp Pimpla luctuosa Smith to a small host species, Galleria mellonella (L.), and a large host species, Mamestra brassicae L., was investigated to test whether female wasps responded to hosts of different sizes across different host species. In the experiments, both host species were presented to each test female wasp. Primary and secondary sex ratio experiments revealed that female wasps laid more female eggs in larger pupae of each host species, indicating that female wasps recognized size differences within host species. The wasp sex ratio (male ratio) from M. brassicae, however, was much higher than that expected on the basis of the sex ratio curve from different-sized G. mellonella. Larger hosts of each host species yielded larger wasps, indicating that the host size estimation by female wasps across different host species was incomplete or was not simple. These results suggested that P. luctuosa evaluated host size not only by physical measures such as dimension but also by other unknown measures. A possible explanation for the adaptiveness of different sex ratio responses by Pimpla luctuosa to different host species was discussed.     

A sex ratio theory of gregarious parasitoids

Summary A mathematical model is constructed to explain a density-dependent increase in the progeny sex ratios of gregarious parasitoids. In the model we considered non-cooperative game between females concerned with their own inclusive fitness. Equilibrium progeny sex ratios of the first and second females ovipositing on the same host are expressed in terms of the probability of double parasitism (p), the ratio of a male to a female in contribution to resource competition (α), the clutch size ratio between the two females (β), the crowding effect on female reproductive success (γ), and the inbreeding coefficient (f). Major predictions from the model are: 1) the progeny sex ratios of both the first and second females increase withp, 2) as β becomes smaller, the progeny sex ratios of the first females decrease, while those of the second females dramatically increases, 3) when a host is attacked by at most two wasps, the sex ratio of the total number of eggs laid on the host does not exceed 0.25. The effects of α and preferential death by female progeny in doubly parasitized hosts are considered as factors responsible for an excess number of males at emergence. Some possible modes of density-dependent increase in the sex ratios of the overall progeny populations is also discussed on the basis of the present model.     

Queen-worker conflict over sex ratio: A comparison of primary and secondary sex ratios in the Argentine ant,Iridomyrmex humilis

We compare the primary sex ratio (proportion of haploid eggs laid by queens) and the secondary sex ratio (proportion of male pupae produced) in the Argentine ant Iridomyrmex humilis with the aim of investigating whether workers control the secondary sex ratio by selectively eliminating male brood. The proportion of haploid eggs produced by queens was close to 0.5 in late winter, decreased to less than 0.3 in spring and summer, and increased again to a value close to 0.5 in fall. Laboratory experiments indicate that temperture is a proximate factor influencing the primary sex ratio with a higher proportion of haploid eggs being laid at colder temperatures. Production of queen pupae ceased in mid-June, about three weeks before that of male pupae. After this time only worker pupae were produced. During the period of production of sexuals, the proportion of male pupae ranged from 0.30 to 0.38. Outside this period no males were reared although haploid eggs were produced all the year round by queens. Workers thus exert a control on the secondary sex ratio by eliminating a proportion of the male brood during the period of sexual production and eliminating all the males during the remainder of the cycle. These data are consistent with workers preferring a more female-biased sex ratio than queens. The evolutionary significance of the production of male eggs by queens all the year round is as yet unclear. It may be a mechanism allowing queen replacement in the case of the death of the queens in the colony.     

Biology of Campoletis chlorideae (Uchida) (Hym., Ichneumonidae) developing in Bt-treated, Bt-resistant Helicoverpa armigera (Hübner) (Lep., Noctuidae) larvae

Abstract:  Life history parameters in two generations of endoparasitoid Campoletis chlorideae (Uchida) were examined using Bacillus thuringiensis (Bt)-resistant Helicoverpa armigera (Hübner) larvae feeding on B. thuringiensis toxin Cry1Ac. In the laboratory, Bt toxin was fed to Bt-resistant host larvae continuously in case of Bt treatment and only before or after the host larvae were parasitized in Bt–P and P–Bt treatments, respectively. C. chlorideae pupae developed faster in Bt treatment than non-Bt treatment. The shortened pupal stage duration was mainly because of the feeding of host larvae on Bt-diet before being parasitized. Body length of adult male C. chlorideae developed inside Bt-treated Bt-resistant (Bt–Bt) H. armigera larvae significantly decreased, especially in host larvae feeding on Bt-diet after being parasitized. However, survival, pupal mortality and adult longevity of C. chlorideae were almost unaffected in Bt-resistant H. armigera larvae feeding on Bt-toxin. Furthermore, Bt-treated host larvae had the same effect on the F₁ progeny of C. chlorideae as the previous generation, and there was no significant difference between generations. This experiment suggests that there is very limited effect on the life history parameters in two generations of C. chlorideae parasitizing Bt–Bt H. armigera larvae. But both generations of C. chlorideae are affected when Bt-resistant H. armigera larvae fed on Bt toxin for different durations.     

Effects of host age, host density and parent age on reproduction of the filth fly parasite Urolepis rufipes (Hymenoptera: Pteromalidae)

Urolepis rufipes Ashmead, a pteromalid wasp, was recently discovered parasitizing house fly and stable fly pupae in eastern Nebraska dairies. Studies have been conducted on the biology of this parasite to evaluate its potential as a biological control agent of stable flies (Stomoxys calcitrans (L.] and house flies (Musca domestica L.). House fly pupae were suitable as hosts for U.rufipes at all ages; however, significantly higher parasitism occurred on host pupae aged 96-120 h. Parasite-induced mortality (host mortality without progeny production) was higher than for other pteromalid parasites of filth flies under similar conditions. Parasitism increased with parasite--host ratio at 20 degrees C; however, the opposite was noted at 30 degrees C for parasite--host ratios ranging from 5:50 to 50:50. Fly eclosion decreased as parasite--host ratio increased at 20 degrees C, and no host eclosion occurred at the highest parasite--host ratios (20:50 and 50:50) at 30 degrees C. Females produced an average of 18.6 female and 7.6 male progeny. 88% of the progeny were produced during the first 6 days post parental eclosion. The short life span, low progeny emergence rate and high per cent host eclosion, in comparison with other parasite species, suggests that the Nebraska strain of U.rufipes may not an effective biological control agent of house flies.