Mass-reared Strain Research Articles

RAPD analysis in the parasitoid wasp Psyttalia concolor reveals Mediterranean population structure and provides SCAR markers

Psyttalia concolor (Szepligeti) (Hymenoptera: Braconidae) is a parasitic wasp reared and released for the biological control of the olive fruit fly Bactrocera oleae (Gmelin) (Diptera: Tephritidae). We used RAPD (Random Amplified Polymorphic DNA) markers to assess the level of genetic differentiation in and between 11 introduced (“wild”) Mediterranean populations (nine from South Italy, and two from the Middle East). The wasp populations from these areas differ for colonization history in terms of original released strain and time of release. We have also considered four mass-reared strains, three derived from Mediterranean wasps and one (Guatemala) from African specimens, in order to infer the degree of their genetic relationships with the considered “wild” Mediterranean samples. The similarity estimates indicate a high level of genetic homogeneity not only within the four mass-reared strains but also within the Italian and Middle East samples. Phenotypic AMOVA and cluster analyses highlight differentiation between the Italian samples and the Middle East samples. As expected, the three Mediterranean mass-reared strains show an intermediate position among the Mediterranean “wild” samples, while a major differentiation characterizes the Guatemala strain. Based on RAPD markers, SCAR (Sequence Characterized Amplified Regions) primers were developed. In the long term, these SCAR markers may offer a powerful tool to monitor the performance of biological control programmes.

DISPERSAL AND LONGEVITY OF WILD AND MASS-REARED ANASTREPHA LUDENS AND ANASTREPHA OBLIQUA (DIPTERA: TEPHRITIDAE)

The rates of dispersal and survival of sterile mass-reared laboratory flies and sterile wild flies of Anastrepha ludens (Loew) and Anastrepha obliqua (Macquart) were estimated and compared with a regular rectangular array of 64 food-baited traps spaced 60 m between traps around the release point in Tapachula Chiapas, Mexico. The traps were scored every day during the first week, and then every 3 d over a 30-d period. For A. obliqua, the number of males recaptured was higher than that of females, while for A. ludens, females were recaptured more frequently than males. The recapture rate for the wild strains ranged from 0.6-24.8% for A. ludens and 1.3-16.2% for A. obliqua and the corresponding ranges for the mass-reared strains were 0.5-7.1% and 0.5-3.0% respectively. The life expectancy was 4.7 d for wild and 4.3 d for mass-reared A. obliqua males but 3 and 2 d, respectively, for wild and mass-reared A. ludens males. The net displacement of A. ludens and A. obliqua ranged approximately from 100-250 m and took place mostly on the first day. Wild A. ludens moved to the northwest from the release point while the mass-reared strain moved to the west. The A. obliqua wild flies moved to the west, while the mass-reared strain shifted to the southwest. We discuss the implications of our findings as to the spacing and frequency of sterile fly releases for the suppression of wild populations.

SEXUAL COMPETITIVENESS AND COMPATIBILITY BETWEEN MASS-REARED STERILE FLIES AND WILD POPULATIONS OF ANASTREPHA LUDENS (DIPTERA: TEPHRITIDAE) FROM DIFFERENT REGIONS IN MEXICO

Abstract The mass-reared colony of Anastrepha ludens (Loew) currently used in Mexico for suppression of the Mexican fruit fly has been in use for over 10 years. Sterile flies are released into a wide range of environmental conditions as part of an integrated area-wide approach to suppress diverse populations of this pest in the Mexican Republic. This paper assesses the performance of the sterile flies interacting with wild populations from the different environments. We investigated the sexual compatibility and competitiveness of the sterile flies when competing with wild populations from 6 representatives Mexican states: Nuevo Leon, Tamaulipas, Sinaloa, Nayarit, Michoacan, and Chiapas. Results show that the males of the wild populations differed in the time to the onset and peak of sexual activity. Nevertheless, the index of sexual isolation (ISI) reflected sexual compatibility between the populations and the mass-reared strain, indicating that the sterile individuals mate satisfactorily with the wild po...

Biodemography of a long-lived tephritid: Reproduction and longevity in a large cohort of female Mexican fruit flies, Anastrepha ludens

Age of sexual maturity, daily and lifetime reproductive rates, and life span were recorded in a laboratory cohort of Mexican fruit flies consisting of over 1100 females maintained individually. The results revealed that, relative to the medfly, the Mexfly is slower maturing (14 vs 17 days), more fecund (1400 vs 650–1100 eggs/female), and longer lived (50 vs 35 days). The results reinforced the generality of several earlier findings on the medfly including the deceleration of mortality at older ages and the weakness of the correlation between the rate of egg laying at early ages and both subsequent reproduction and remaining longevity. Discussion includes perspectives on the role of artificial selection in shaping the demographic traits of the mass-reared strain of Mexfly used in this study, as well as the overall significance of large scale biodemographic studies in understanding aging and longevity.

Can the Okinawa mass-reared strain of the melon fly, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae) mate with the Taiwan wild strain?

Mating tests between Okinawa mass-reared and Taiwan wild strains of the melon fly, Bactrocera cucurbitae (Coquillett), were conducted in transparent acrylic plastic cages in the laboratory. The Okinawa mass-reared strain has been cultured for about 150 generations under artificial rearing conditions. The two strains of melon fly could mate with each other. Moreover, no significant assortative or disassortative mating was observed. Therefore, we suggest that the Okinawa mass-reared melon fly is compatible of mating with the Taiwan wild melon fly, at least under the laboratory conditions employed here.

INFLUENCE OF ADULT DIET ON THE MATING SUCCESS AND SURVIVAL OF MALE MEDITERRANEAN FRUIT FLIES (DIPTERA: TEPHRITIDAE) FROM TWO MASS-REARING STRAINS ON FIELD-CAGED HOST TREES

Using field-caged host trees, this study investigated the influence of adult diet on the mating success and survival of male Mediterranean fruit flies, Ceratitis capitata (Wied.), from two mass-rearing strains. Upon emergence, males from a genetic sexing (temperature sensitive lethal) strain and a bisexual strain were given either a sugar-protein diet (protein-fed) or a sugar-only diet (protein-deprived). Mating trials were conducted using field-caged host trees, and 100 males of a given strain and diet competed with 100 wild males for matings with 100 wild females (all wild flies were given the sugar-protein diet). There was no apparent effect of diet on male mating success for either mass-reared strain. Wild males obtained significantly more matings per replicate than males from either strain on either diet, and the mean number of matings per replicate was similar between protein-fed and protein-deprived males for both strains. In addition, the survival of protein-fed and protein-deprived males was compared over 2- and 4-day intervals on field-caged host trees. Within each mass-reared strain, there was no apparent effect of adult diet on male survival for either test interval. The present findings are compared with similar studies on other mass-reared strains.

EXPOSURE TO GINGER ROOT OIL ENHANCES MATING SUCCESS OF MALE MEDITERRANEAN FRUIT FLIES (DIPTERA: TEPHRITIDAE) FROM A GENETIC SEXING STRAIN

In the Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann), exposure to α-copaene, a botanically derived male attractant, and ginger root oil (GRO), Zingiber officinale (Roscoe), which contains α-copaene, increased the mating success of wild males, and GRO enhanced mating competitiveness of mass-reared males from a bisexual, mass-reared strain. The present study extends this research by examining the effects of GRO exposure on the mating success of mass-reared males from a genetic sexing strain based on a temperature sensitive lethal (tsl) mutation. Such strains are currently used for nearly all sterile insect technique (SIT) programs for this insect. In addition, potential negative effects of GRO exposure on male survival and female remating propensity were investigated. Following exposure to GRO, males from the tsl mass-reared strain showed enhanced mating performance against wild-like males from two recently established colonies. Against wild-like males from a Guatemala strain, the proportion of matings obtained by males from the tsl mass-reared strain increased from 16% per replicate for non-exposed (control) individuals to 30% for GRO-exposed (treated) individuals. Against wild-like males from a Madeira strain, the proportion of matings obtained by treated, tsl mass-reared males was 39% per replicate compared to only 16% for control, tsl mass-reared males. Survivorship was similar between GRO-exposed and non-exposed males from the tsl strain, and females mated initially to treated or control tsl mass-reared males displayed similar remating propensity. The application of pre-release, GRO-exposure to males in the SIT against medfly is discussed.

VARIATION IN THE INTERMITTENT BUZZING SONGS OF MALE MEDFLIES (DIPTERA: TEPHRITIDAE) ASSOCIATED WITH GEOGRAPHY, MASS-REARING, AND COURTSHIP SUCCESS

Many aspects of the temporal pattern of sounds produced during the intermittent buzzing displays of pre-copulatory courtship by male medflies varied between wild flies from Costa Rica, Argentina, and Hawaii, and between mass-reared flies from Costa Rica, Argentina, Mexico, and Hawaii. There were no consistent differences when mass-reared strains were compared with the wild strains from the area where they originated in Costa Rica, Argentina and Hawaii. Buzzing sounds produced prior to successful mounting attempts did not differ consistently from those preceding unsuccessful mounts in flies from Costa Rica and Argentina. In strains from all sites, however, courtships in which buzzes were interrupted were more likely not to result in mounting of the female. There was a weak tendency for interruptions to be more common in mass-reared strains.

Increased density and male–male interactions reduce male longevity in the medfly, Ceratitis capitata

We investigated the effect of adult density on male and female longevity and behavioural interactions in a mass-reared strain of the medfly. Male survival decreased significantly, and male–male behavioural interactions increased significantly, with increasing male density (males were kept at 1, 2, 6 and 10 flies per 285cm2in pots of 5.5cm in diameter and 12cm high). No such effects were observed in females over the same density range. This suggests that male survival decreased in response to the deleterious effects of male–male behavioural interactions. At the highest density, courtship wing fanning directed towards other males decreased significantly over time. In addition, as either density or male-biased sex ratio increased, males were increasingly likely to be engaged in courtship wing fanning that was not directed towards females. These results suggest that high adult density may significantly reduce male reproductive success, by decreasing survival and mating success. The results highlight the potentially high survival costs of male–male interactions and indicate differences in the nature of reproductive costs in the two sexes.

Exposure to ginger root oil enhances mating success of irradiated, mass-reared males of Mediterranean fruit fly (Diptera: Tephritidae).

Previous research revealed that exposure to ginger root oil, Zingiber officinale Roscoe, containing the known male attractant (a-copaene) increased the mating success of male Mediterranean fruit flies, Ceratitis capitata (Wiedemann), from a newly established laboratory colony. The goal of the current study was to determine whether exposure to ginger root oil likewise enhanced the mating competitiveness of irradiated C. capitata males from a 5-yr-old mass-reared strain. Mating tests were conducted in field cages containing guava trees (Psidium guajava L.) to monitor the mating frequency of irradiated, mass-reared and wild males competing for wild females. In the absence of chemical exposure, wild males outcompeted the mass-reared males and obtained 74% of all matings. However, following exposure to ginger root oil (20 microl for 6 h), the mating frequencies were reversed. Whether exposed as mature (3-d-old) or immature (1-d-old) adults, mass-reared males achieved approximately 75% of all matings in tests conducted 2 or 4 d following exposure, respectively. Irradiated, mass-reared males prevented from contacting the oil directly (i.e., exposed to the odor only for 6 h) still exhibited a mating advantage over wild males. In an additional study, signaling levels and female arrivals were compared between males exposed to ginger root oil and nonexposed males, but no significant differences were detected. The implications of these findings for the sterile insect technique are discussed.

Short-term changes in consumption and oviposition rates of Neoseiulus californicus strains (Acari: Phytoseiidae) after a diet shift.

Short-term effects on consumption and oviposition rates of four strains of Neoseiulus californicus (McGregor) after a diet shift were evaluated. The new feeding conditions experienced by the predators were six fixed densities of eggs or protonymphs of Tetranychus urticae Koch placed on excised strawberry leaflet discs and maintained under laboratory conditions (25 +/- 1 degrees C, 75-85% RH, 16L: 8D). The observations were made on the first and the fifth day of the experiment. The phytoseiids came from three long-term mass-reared strains fed on T. urticae, Dermatophagoidesfarinae Hughes, or Quercus spp. pollen, respectively. The fourth strain was collected directly in a strawberry field. Time since diet transfer can be added to the factors (i.e. feeding history and prey density) already known to affect the functional and numerical responses of N. californicus, both when it feeds on prey eggs and protonymphs. If consumption rates were averaged over all strains and densities, 9.04 and 11.41 eggs, and 6.97 and 6.48 protonymphs were consumed on the first and the fifth day, respectively. If the same was done for oviposition rates, predators feeding on eggs produced 1.46 and 2.36 eggs/female/day, whereas predators feeding on protonymphs produced 1.35 and 2.29 eggs/female/day. Time had the greatest impact on the functional response of the strain that had previously fed on tetranychids, while an effect of time on the numerical response was detectable in all strains.

Genetic sexing strains of mediterranean fruit fly (Diptera: Tephritidae): quality in mass-reared temperature-sensitive lethal strains treated at high temperatures.

The high-temperature treatment of eggs of mass-reared tsl genetic sexing strains in Mediterranean fruit fly, Ceratitis capitata (Wiedemann), during late embryogenesis (the low-high protocol) conserves more male flies than treatment during early embryogenesis. A tsl strain, AUSTRIA 6-97, was constructed to follow the fate of aneuploid individuals during male-only production. Aneuploid individuals are produced following segregation in the translocation heterozygous males, and they can survive to the pupal stage where they compromise quality because they do not eclose as adults. Hatching, emergence, and male fly production were quantified and the heat-treatment protocol was characterized. The low-high egg treatment conserves the number of euploid-balanced males, and there is a very low survival of aneuploid males. After heat treatment of eggs, at least 95% of the male pupae were euploid compared with only 71% from untreated eggs. The quality of euploid male pupae was diminished with successive daily collections, an effect previously attributed to aneuploid survivors. Reduced yield of euploid males from early heat treatments was the result of an emergence effect, in addition to a maternal effect. A third detrimental effect of heat was found, occurring after hatching and before pupation, that reduces the survivorship of euploid males. The low-high treatment protocol yielded more males, with a higher accuracy than other heat treatments. However, although it avoids both the maternal and emergence effects, the production of euploid males was 30% less than the potential production, implying that the low-high heat protocol for killing female embryos in tsl genetic sexing strains can be fine-tuned.

Long-term changes in age-specific egg production of two Bactrocera cucurbitae (Diptera: Tephritidae) strains mass-reared under different selection regimes, with different egg collection methods.

Two mass-reared strains of the melon fly, Bactrocera cucurbitae (Coquillett), showed contrasting oviposition patterns throughout a period of long-term culture. The two strains, established in 1980 (old strain) and 1985 (new strain), were maintained in a sterile insect technique project in Kagoshima Prefecture, Japan. During the first several generations of small-scale rearing of the two strains, selection for increased production efficiency was applied. As a result, an early-reproduction trait developed more rapidly in the new strain than in the old strain. After the selection was ceased, an early-reproduction trait developed in the old strain for 25 generations of large-scale mass rearing; there was no further development of the early-reproduction trait in the new strain. The result obtained with two-way selection for age at reproduction suggested that the new strain had been nearly at the selection limit for early reproduction at the beginning of mass rearing. The following two rearing conditions may be responsible for the observed differences in oviposition patterns of the two strains: differences in the selection regimes during the small-scale rearing and differences in the egg-collection methods used in the subsequent course of mass rearing of the strains.

New Indices and Method to Measure the Sexual Compatibility and Mating Performance of Ceratitis capitata (Diptera: Tephritidae) Laboratory-Reared Strains Under Field Cage Conditions

The method to assess the sexual compatibility and mating performance of Mediterranean fruit fly, Ceratitis capitata (Wiedemann), mass-reared strains has been revised. Three new indices (isolation index, ISI; male relative performance index, MRPI; female relative performance index, FRPI) that look at the relative impact of both male and female population on the sexual isolation between laboratory and wild strains are described. The methodology and the indices were used in Argentina to test the SEIB 6–96 genetic sexing strain in competition with wild C. capitata population from the Patagonia region. The experiments show that the 2 populations are sexually compatible (ISI = 0.309). SEIB 6–96 sterile males compete with wild males, achieving 1 out of 4 Patagonian female mates. Using the current method as a decision tool, SEIB 6–96 sterile males are released weekly in Patagonia since September 1997. The accuracy of the 3 new indices is compared with the indices previously available. The possible application of the method and the indices in SIT operational programs world-wide is discussed.

Assessment of Amblyseius fallacis (Acari: Phytoseiidae) for biological control of tetranychid mites in an Ontario peach orchard.

We introduced a mass-reared pyrethroid-resistant strain of the predatory phytoseiid mite Amblyseius fallacis (Garman) into an Ontario peach orchard in an attempt to control populations of the phytophagous mites Panonychus ulmi Koch and Tetranychus urticae Koch (Acari: Tetranychidae). Releases of 1,000 and 2,000 mites per tree were made, at three different times. The release of 2,000 mites per tree in June and in July resulted in significantly higher phytoseiid densities than was observed on control trees. However, densities of P. ulmi or T. urticae were not significantly affected by any release rate or by timing. The release of 1,000 A. fallacis per tree, or of any density in August, did not significantly increase phytoseiid abundance. In the following year, population dynamics of both phytoseiid and phytophagous mites were not significantly affected by the previous year's release. Amblyseius fallacis can be a useful predator in some fruit orchards. However, further research is necessary into the timing and rate of release, modified spray programmes, and with different crops, in order to clarify the role of this species for biological control in Ontario peach orchards.

Genetic Sexing Strains of Mediterranean Fruit Fly (Diptera: Tephritidae): Optimizing High Temperature Treatment of Mass-Reared Temperature-Sensitive Lethal Strains

Genetic sexing systems based on a temperature-sensitive lethality have been developed for mass-reared Mediterranean fruit fly, Ceratitis capitata (Wiedemann). This study shows that the timing of high temperature treatment (34°C) of eggs of temperature sensitive lethal ( tsl ) C. capilata affects the number and accuracy of production of males. High-temperature treatment during late embryogenesis (24-48 h after egg collection) produced more male flies compared with treatment during early embryogenesis (0 -24 h after egg collection). The principal impact of the heat treatment was on egg hatch. Treatment during early embryogenesis resulted in 38.2%hatch, whereas treatment during late embryogenesis resulted in 55.5%hatch. Treatment during late embryogenesis conserved nearly all potential males, produced >99.5% males, and will improve the economy of male production for large scale tsl C. capitata rearing. Results support the existence of a maternal effect during the first 24 h of embryogenesis. Lethality in males occurred during the early part of embryogenesis, when male embryos were still dependent on the egg cytoplasm for development. Heat treatment did not eliminate aneuploid individuals as expected, but it did reduce a proportion of them. Some aneuploid individuals pupated, although many failed to emerge as adults. The frequency of aneuploid individuals increased throughout consecutive larval collections, resulting in decreased emergence and decreased pupal volume. These data suggest that it is not economical to collect larvae after day 3 or 4.

Medfly courtship duration: a sexually selected reaction norm changed by crowding

The evolutionary effects of crowding on male courtship behavior were studied using wild and mass-reared medflies. Mass-reared strains had been raised under highly crowded conditions in mass-rearing facilities for approximately 75, 180, and 238 generations. Pre-mounting courtship was facultatively shortened in both wild and mass-reared males under conditions of greater crowding. The courtship behavior of males of mass-reared strains was also shorter than that of wild males under similar conditions of crowding. Shorter courtships are probably advantageous for males in crowded conditions because they reduce the likelihood of the courtship being interrupted by other flies. Several types of data indicated that males rather than females were responsible for shortened courtships. We conclude that heritable variation in male courtship behavior has persisted in a wild population despite its overall relatively low genetic variability, and that genetic changes in mass-reared strains have altered the range of facultative adjustments in courtship behavior.

Remating inhibition in the melon fly,Bactrocera (=Dacus) cucurbitae (Diptera: Tephritidae): Copulation with spermless males inhibits female remating

Eight hour copulation of the melon fly,Bactrocera cucurbitae, which usually mates at dusk and finishes copulation at dawn, inhibited female remating, while 3 h copulation did not. Copulation of females with either normal or virgin sterile males inhibited female remating. Sperm-depleted sterile males inhibited female remating at the same rate as normal males when the copulation duration was 8 h, indicating that existence or amount of sperm in females' spermathecae is not important in remating inhibition. Females of a wild strain remated later than females of a mass-reared strain, irrespective of strains of 1st and 2nd males. This suggests that the females may control their own remating, or that there is a difference between wild and mass-reared strains in their sensitivity to a male substance that inhibits females' receptivity.

Interaction of Wild Males and Laboratory-Adapted Females of the Mexican Fruit Fly (Diptera: Tephritidae) in Natural Habitats

Despite >40 yr of ecological and behavioral research on reproductive interactions involved in sterile insect release programs, experimental measurement of the intensity of intermale competition for mates and the role of sterile females in these programs has rarely been addressed. Experiments described in this study were designed to evaluate these factors. Virgin females from a mass-rearing strain (mass reared for 36 yr) of the Mexican fruit fly, Anastrepha ludens (Loew), were released and subsequently recaptured along with native Mexican fruit flies in natural habitats in Nuevo Leon, Mexico. Tests were carried out at six locations and replicated four times. Recaptured females were dissected to determine mating status. Data were analysed to determine whether the released females mated with native males, and to evaluate the influence of test site, test date, and wild male and female density on rates of recapture of the released females and their mating status. Results showed that 5–50% of the recaptured females mated with native males. This indicates that released females (even from a strain adapted to mass rearing) may occupy a significant amount of native male reproductive effort and that males in native populations have excess reproductive capacity. Number of native males captured per test was significantly correlated with the percentage of mated females. Plots of percent mating versus number of native males captured showed that when number of captured males was high, percent females mated was always high, but when numbers of males captured was low, percent mating could still be high. A severe freeze during the fourth test greatly reduced the native population. Released females were recaptured up to 7 wk after release and 4 wk after the freeze, indicating that the mass-reared strain had sufficient physiological-behavioral tolerance to survive extreme environmental stress.

Male Recombination in a Genetic Sexing Strain of Ceratitis capitata (Diptera: Tephritidae) and Its Effect on Stability

Male recombination was studied between the Y-translocated loci or (orange eye) and wp (white pupae) in a genetic sexing strain of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann). This strain normally produces wild type males, whereas females are homozygous for the or and wp alleles. In previous mass rearing, another strain with the same translocation was highly unstable. In this study, an overall male recombination frequency of 0.07 and 0.24% was observed between the or gene and the translocation breakpoint (T) and between wp and T, respectively. Only one of the two alleles appeared to be physically linked to the Y chromosome. All aberrant male phenotypes still contained the translocation, indicating that no reversal to the normal karyotype had taken place. A strong positive interference on recombination was observed; a recombinant event between T and wp led in one-third of the cases to a recombinant event also occurring between T and or . Male recombination appeared to be responsible for the initiation of the breakdown of the mass-reared genetic sexing strain, but it could not by itself account for the subsequent rate of breakdown of this strain. The possible role of other factors in accelerating the rate of this breakdown is discussed.