Times for recovery from cold-torpor in the Queensland fruit fly Dacus tryoni: the relation to temperature during and after chilling

Recovery time after experience of a given minimum temperature below torpor threshold is related to the value of that minimum, the length of time spent at that minimum, and the temperature prevailing during the recovery period above torpor threshold. A model can predict recovery time for flies experiencing a given temperature fluctuation if the length of time spent at the minimum is expressed as a proportion of LE₅₀ at that minimum.The model has applications in defining the optimal protocol for chilling insects for use in the Sterile Insect Release Method. The model was confirmed by experiments showing that it is likely that flies will recover from non-lethal frosts before ant predators become active.

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Résumé Le temps de récupération après avoir subi une température minimal située au-dessous du seuil d'engourdissement dépend de la valeur de ce minimum, du temps passé à ce minimum, et de la température au-dessus du seuil d'engourdissement pendant la période de récupération. Un modèle mathématique permet d'estimer le temps de récupération après avoir subi une chute de température déterminée, en fonction du temps passé au minimum thermique exprimé comme une fraction du LE₅₀ (temps nécessaire pour tuer 50% des mouches) à ce minimum.Ce modèle s'est trouvé étayé par des observations montrant qu'il est probable que les mouches se remettent des gelées sublétales avant la reprise d'activité des fourmis prédatrices. Ce modèle peut être utilisé pour définir les conditions optimales de refroidissement des insectes utilisés lors de la libération d'individus stériles.

     

Mark-recapture estimates of overwintering survival of the Queensland fruit fly,Dacus tryoni,in field cages

1. Four groups of 75 pairs each of marked adult Dacus tryoni that had emerged from field-collected guavas were liberated into cage-covered guava trees at the end of May, 1960 and sampled at weekly intervals to estimate the overwintering survivorship.
2. Estimates of numbers were made using three different methods as described byLeslie (1952) and one byJolly (1965). The Method A, approximate Method B andJolly models gave quite similar results although the Method A model was shown to be more sensitive to stochastic changes in the R/r ratios. The complete Method B model produced much smaller variances, due to its full utilization of the information in the data but it was very sensitive to small biases—even those caused by the restriction that recaptures must be whole numbers—and thus could not quite approach the exact expectations.
3. Although in some instances, statistical tests (Leslie , 1958) showed some significant deviations from randomness in recapture, these were not appreciable and did not affect the estimates.
4. When sufficient food was available, the flies in the field cages exhibited survival rates during the winter months of 1960 quite comparable to those of laboratory flies kept at room temperature with several exceptions: (a) there was a high mortality among the newly emerged flies during the initial week after release, (b) a high mortality during the last week of June and (c) a high mortality during the third week in July and the end of August which can be correlated with lack of rain, low humidity and warm daytime temperatures. Low temperatures apparently had little effect on survival.
5. There was no difference in the survival of males and females.
6. One replicate cage, whose flies had been anesthetized with carbon dioxide prior to release, exhibited significantly higher mortality rates than the other replicates.
7. Data from a fifth cage indicated that females were not inseminated during the winter months and did not produce mature eggs until the beginning of September.

     

Attractants for the gravid Queensland fruit fly Dacus tryoni

The vapours of certain pure chemicals, typical of ripe fruits, elicited characteristic components of ovipositional behaviour from gravid Dacus tryoni (Froggat) in an olfactometer: the flies walked and flew upwind to the source of the vapour and then probed with their ovipositors. A range of alcohols, acids, ketones and esters having 2–6 carbon atoms were effective (1 and 10% of iso-butyric acid, n-butyric acid, methyl butyrate, ethyl butyrate, 2-butanone, ethyl lactate and ethyl acetate; and 10% concentrations of ethanol and 2-propanone). The most effective were 4–6 carbon acids, esters and ketones. Behavioural threshold for n-butyric acid vapour at 26°C was obtained from a 5×10^–3% dilution in paraffin oil; maximum fly response occurred at about 200 times this concentration. Low concentrations of the 15-carbon sesquiterpene, -farnesene, were also very effective, despite its lower volatility. These results suggest that at least three different types of alfactory sensory neurones are involved in the identification of fruit attractants by gravid D. tryoni.     

Genetic and molecular markers of the Queensland fruit fly, Bactrocera tryoni

Twenty-six microsatellite markers, along with two restriction fragment length polymorphism (RFLP) markers and three morphological markers, have been mapped to five linkage groups, corresponding to the five autosomes of the Queensland fruit fly, Bactrocera tryoni. All these molecular and genetic markers were genotyped in three-generation pedigrees. Eight molecular markers were also localized to the salivary gland polytene chromosomes by in situ hybridization. This provides a substantial starting point for an integrated genetic and physical map of B. tryoni.     

The integument of the Queensland fruit fly,Ddacus tryoni (Frogg.)

Summary During the pupal stage of Dacus tryoni, the hypodermis of the larva is replaced by an imaginal generation of smaller cells. The hypodermal cells of the tergal glands on the fifth abdominal segment of the adult were examined with the electron microscope; they contain slender, membrane-limited bundles of hollow wax filaments that traverse the cuticle in branched pore canals. Outside the glandular areas, the pore canals are narrower. The cuticle of the adult undergoes its greatest increase in thickness soon after emergence; it becomes sclerotized gradually. No epicuticle was detected with either the light or electron microscopes.Early in adult development, bristles are formed over the general surface of the terga. Most of these are innervated by single, bipolar nerve cells, and have more or less enlarged trichogen cells that appear to secrete wax through pore-plates in the cuticle. The bristles in different regions of the abdomen range in function from pure sensory receptors to pure secretors. The sensory bristles on the tergal glands were examined with the electron microscope.For assistance with the electron microscopy, I thank Mr. Tony Webber and Miss Ann Miller of the Electron Microscopy Unit at Sydney University. — Supported by a C.S.I.R.O. Junior Post-Graduate Studentship.     

The role of adult learning in the acceptance of host fruit for egglaying by the Queensland fruit fly, Dacus tryoni

Evidence presented indicates that exposure of wild Queensland fruit files, Dacus tryoni (Froggatt), to a given host fruit type (e.g. pear) for 3 days causes females to attempt oviposition to a greater degree in that fruit type than in other fruit types (e.g. tomato, grape). The effects of exposure to a particular fruit type proved reversible, suggesting that D. tryoni females were capable of learning. Females exposed to pear for 3 days appeared to retain the effect of such exposure on acceptance of tomato for up to 4 days but appeared to retain the effect on acceptance of grape for less than 2 days. The possible significance of prior experience of females with a particular fruit type on future ability to discriminate among varying-quality specimens of that type is discussed.

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Résumé Les éléments apportés montrent que l'exposition de D. tryoni Froggat à un type de fruit déterminé (par exemple, la poire) pendant 3 jours, conduit la femelle à tenter de pondre à une plus haute fréquence dans ce type de fruit que dans d'autres (par example; tomate ou raisin). Les effects de l'exposition à un type particulier de fruit étant réversibles, ceci suggère que les femelles de D. tryoni sont capables d'apprentissage. Des femelles exposées à des poires pendant 3 jours ont conservé l'effet d'une telle exposition pendant 4 jours en présence de tomates, mais moins de 2 jours en présence de raisin. La discussion porte sur la signification possible de la connaissance antérieure d'un type particulier de fruit sur l'aptitude ultérieure des femelles à distinguer parmi des spécimens de ce type, mais de qualités différentes.

     

Upwind anemotaxis in response to cue-lure by the Queensland fruit fly, Bactrocera tryoni

Movements of mature male Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) were observed individually in a wind tunnel under conditions of ‘cue-lure with wind’, ‘cue-lure with no wind’, ‘wind only’ and ‘no wind or cue-lure’. Further observations were made using a dense foliage array in the wind tunnel and a structured plume of cue-lure. Patterns of walking or flying were essentially the same in all of the first four treatments except that in the ‘cue-lure with wind’ treatment, over half of the flies moved in a consistent track upwind for at least 400 mm at some time during the first 5 min of observation. With clean wind, only 10% of the flies did this. The result was that mean net upwind displacement after 5 min in the ‘cue-lure with wind’ treatment significantly exceeded that in the other three treatments, the results of which did not differ significantly from each other. The upwind tracks were accomplished by either walking or flying (with or without stops) or by a combination of both. When the wind tunnel was filled with a dense foliage array, the results with cue-lure laden wind were similar to those obtained with the equivalent treatment without foliage, except that upwind tracks were predominantly in short stages. When flies were exposed to a structured plume of cue-lure odour (without foliage present), they did not apparently alter their behaviour on leaving or entering the plume, but some did make consistent upwind tracks while they were in the plume.     

Experimental analysis of the pattern of tethered flight in the Queensland fruit fly, Dacus tryoni

ABSTRACT. The tethered flight of the Queensland fruit fly, Dacus tryoni Frogg. (Diptera, Tephritidae), was investigated, and the duration of each flight during a 2-h experimental period was recorded. The pattern of flight was analysed, and related to the age, sex and origin of the specimens, and to the availability of host fruit during the rearing of the adults. The effect of adult crowding on the pattern of flight was also briefly examined. The results indicated that the origin of the flies had little effect on the pattern of flight; male and female flies showed different trends with respect to the proportion of short flights undertaken as the flies matured; and the availability of fruit had a marked effect on the pattern of flight in recently mature flies. These data are discussed with respect to the dispersive/non-dispersive movements of the flies postulated from previously documented field data. It is suggested that there is a characteristic pattern of tethered flight, which can be related to the absence of hosts in the immediate environment, and would be likely to lead to greater dispersal under natural conditions.     

Critical periods for developmental acclimation to cold in the Queensland fruit fly, Dacus tryoni

Rapid acclimation to cold can occur in Dacus tryoni during two short stages of its life history: the stage immediately prior to the “hopping larva” phase and the “pharate adult” stage within the puparium. Transfer from 25 to 15°C at either of these stages can produce full acclimation to cold within a few days. Acclimation is not detectable at other times in puparial life: during adult life it takes over 100 days.     

Rapid acclimatization to low temperature in the Queensland fruit fly, Dacus tryoni

Dacus tryoni, which overwinters in conditions of wide diurnal fluctuations in temperature, is capable of rapid acclimatization with respect to thresholds for torpor and flight but ability for metabolic compensation is apparently lacking. The rate of reacclimatization on abrupt transfer to lower temperatures is quicker the less the temperature drops and extrapolation of this relationship suggests a time of the order of 1 min for a drop as small as 1°C. This explains why continuous reacclimatization appears to take place during gradual cooling, even when this is as fast as 1°C/min. The insect can rapidly produce its maximum response to extensive drops of temperature as long as the latter falls gradually at a rate no faster than 1°C/min. Acclimatization in nature is therefore ‘immediate’. Reacclimatization to higher temperatures (deacclimatization to cold) depends upon the temperature that the insects are raised to and thus is slower the smaller the rise and understandably is not accomplished more rapidly by a gradual transition.     

Survival of step and ramp changes of temperature by the Queensland fruit fly, Dacus tryoni

ABSTRACT. Survival time at subzero temperatures is related to both long-term thermal history and the rate at which the insects are cooled. Insects cooled at one degree per hour survive for up to 3 times as long at a given test temperature than do insects cooled at 1C/min. Survival times are significantly shorter than times taken to freeze. Survival time at an extreme high temperature is related to long-term thermal history but the rate of heating makes no difference.     

The influence of host fruit morphology on parasitization rates in the Caribbean fruit fly,Anastrepha suspensa

Among the host fruits of the Caribbean fruit fly there are a variety of sizes and shapes. These morphological differences may influence the vulnerability of the larvae to parasites. In the laboratory, Caribbean fruit fly larvae placed in the smaller of 2 different sizes of artificial ‘fruit’ (cloth spheres filled with a diet material) were parasitized at a higher rate by the braconid,Diachasmimorpha longicaudata (Ashmead) when spheres were presented separately. However, when parasites were simultaneously presented with 6 different sizes of ‘fruit’ there was no significant relationship between size and parasitization rate. This may be due to the parasites preference to search for larvae in larger ‘fruit’. In field collections of different species of host fruit, a significant inverse correlation exists between fruit radius and rate of parasitization. However, host fruit size accounts for only about 5% of the variance in yearly parasitization rates.      

Cost of reproduction in the Queensland fruit fly: Y-model versus lethal protein hypothesis

The trade-off between lifespan and reproduction is commonly explained by differential allocation of limited resources. Recent research has shown that the ratio of protein to carbohydrate (P : C) of a fly''s diet mediates the lifespan–reproduction trade-off, with higher P : C diets increasing egg production but decreasing lifespan. To test whether this P : C effect is because of changing allocation strategies (Y-model hypothesis) or detrimental effects of protein ingestion on lifespan (lethal protein hypothesis), we measured lifespan and egg production in Queensland fruit flies varying in reproductive status (mated, virgin and sterilized females, virgin males) that were fed one of 18 diets varying in protein and carbohydrate amounts. The Y-model predicts that for sterilized females and for males, which require little protein for reproduction, there will be no effect of P : C ratio on lifespan; the lethal protein hypothesis predicts that the effect of P : C ratio should be similar in all groups. In support of the lethal protein hypothesis, and counter to the Y-model, the P : C ratio of the ingested diets had similar effects for all groups. We conclude that the trade-off between lifespan and reproduction is mediated by the detrimental side-effects of protein ingestion on lifespan.     

Factors affecting the dispersal of large‐scale releases of the Queensland fruit fly,Bactrocera tryoni

This study investigated two factors potentially affecting the spatial distribution of Queensland fruit fly Bactrocera tryoni (Froggatt) after release from a single point. First, the effect of age at release was investigated using a single cohort of 205 000 males from a mass‐rearing strain used for sterile insect releases. Approximately half were released as immature males and the remainder as sexually mature males (1 week later). Males were collected over 3 weeks from a grid of 135 traps, each containing a pheromone/insecticide bait, positioned between 4 and 500 m from the release point. Variation in the distribution of fly density around the release point was assessed by regressing trapped fly counts against distance. Unexpectedly, no significant differences were found in the spatial distribution of the flies. Second, the effect of inbreeding on spatial distribution was investigated using replicated simultaneous releases of two strains of B. tryoni. One strain was the existing (inbred) mass‐rearing strain that has been selected for high productivity in a mass‐rearing facility. The second strain was deliberately outbred but also selected for high productivity. Almost 100 000 males of each strain were released over the two experiments. Regression of trappings against distance differed significantly between strains in only one of five releases, but in all cases the outbred strain had a greater dispersal distance. As our trapping grid was not regular but contained gaps of up to 100 m, a small preliminary experiment investigated whether flies move faster along tree rows or across open fields. At distances up to 100 m, we found no detectable difference in fly distributions. These results are primarily relevant to the large‐scale point releases carried out as part of an existing B. tryoni sterile insect programme and are discussed in that context.     

Thermal constraints to successful development of the Queensland fruit fly in regimes of constant and fluctuating temperature

Temperature can affect the survival rate through each immature stage of life history and hence the rate of survival from egg to adult emergence. This phenomenon was investigated experimentally by using both regimes of constant temperature and ones in which temperatures fluctuated on a daily basis with rates of heating and cooling approximating to those found in the field. In fluctuating regimes, the highest temperatures tolerated for a few hours on a daily basis were higher than those tolerable on a constant basis. The highest tolerable daily maximum was influenced to some extent by the daily minimum. Regimes near the tolerable threshold that were experienced during one stage of the life history adversely affected the survival rate during the next stage, even if the latter experienced optimal conditions. The results in dicate that, in nature, survival from egg to adult is unlikely if daily maxima prevail in the region of 38–40°C for more than 7 days.

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Affectien de température sur le développement couronné de succès chez Dacus tryoni dans des régimes à des températures constantes et fluctuantes

Résumé La température peut affecter le taux de survie, pour chaque stade d'immaturité, dans l'histoire d'une vie et d'où le taux de survie de l'oeuf à son apparition adulte. Ce phénomène a été étudié à titre expérimental en utilisant les deux régimes à une température constante et l'un d'eux à des températures variées sur une base journalière avec un taux approximatif de chauffage et refroidissement comme ceux que l'on trouve dans ce domaine.Dans un régime de fluctuation, les températures les plus élevées pendant quelques heures sur une base journalière étaient plus fortes que celles tolérées sur une base constante.La maximum journalier de la température la plus élevée supportable était influencé, jusqu'à un certain point, par le minimum journalier.Les régimes qui ont fait l'expérience proche du seuil du supportable au cours d'un stade, dan l'histoire d'une vie, on affecté défavorablement le taux de survie du stade suivant, même si ce dernier a expérimenté les conditions optimal.Les résultats indiquent que, dans la nature, la survie d'oeuf à adulte est improbable si le maxima journalier de 38–40°C prédomine dans la région pendant plus de 7 jours.

     

The dynamics of ovarian maturation and oocyte resorption in the Queensland fruit fly, Dacus tryoni, in daily-rhythmic and constant temperature regimes

The rate of oocyte development in constant regimes corresponded to the rates predicted by Pritchard's (1970) relationship which indicates that the lower temperature threshold is 13.5dgC. Rates in fluctuating regimes indicated that development occurs at certain temperatures below the constant threshold if these are alternated with higher temperatures on a daily basis
In certain fluctuating regimes, oocyte development occurred at a rate in excess of 3.5% per day and maturation proceeded to completion. In such regimes resorption occurred only if egg laying was prevented; when this happened the terminal oocytes usually remained intact and the penultimate ones were resorbed. In other fluctuating regimes, oocyte development proceeded at a rate of less than 3.5% per day and no maturation was achieved because the most advanced oocytes were resorbed-either before or during the vitellogenic phase.
The 3.5% threshold corresponds to a value of 2 day-degrees per day (2DDPD) above 13.5C. Resorption, but no development, was observed in partly mature flies around O DDPD, whereas neither occurred in a still colder regime. These results are shown to be in accord with Fletcher's (1975) field data which are also used to discuss the significance of resorption. Finally, the DDPD relationship is used to define those daily temperature profiles which may permit maturation in the field.     

Development and ultrastructure of the fat body cells and oenocytes of the Queensland fruit fly,Dacus tryoni (Frogg.)

Summary Half-way through the larval period in Dacus tryoni, the fat body cells begin to accumulate protein in the form of granules. Early in the pupal period, both the fat body cells and oenocytes become free in the body cavity. Meanwhile, an imaginal generation of hypodermal cells, while in the process of displacing the larval hypodermis, gives rise to an imaginal generation of oenocytes. Soon after, imaginal fat body cells also appear. A few days after emergence, the larval fat body cells and oenocytes disintegrate and their imaginal equivalents expand to fill the body cavity.This paper also describes the ultrastructure of the larval and imaginal fat body cells and of the imaginal oenocyte. In all three, tubular invaginations of the plasma membrane occupy the peripheral cytoplasm. At most stages, the fat body cells contain a considerable quantity of slightly distended, rough endoplasmic reticulum, which suggests that when these cells are not sequestering protein, they are secreting it into the blood. The imaginal oenocytes are packed with smooth endoplasmic reticulum, which supports other evidence that they participate in the synthesis of cuticular wax.For assistance with the electron microscopy, I thank Mr. Tony Webber and Miss Ann Miller of the Electron Microscopy Unit at Sydney University. For the loan of some sectioned material, I am grateful to Dr. D. T. Anderson.     

Germ-line transformation of the Queensland fruit fly, Bactrocera tryoni, using a piggyBac vector in the presence of endogenous piggyBac elements

We report the heritable germ-line transformation of the Queensland fruit fly, Bactrocera tryoni, using a piggyBac vector marked with either the fluorescent protein DsRed or EGFP. A transformation frequency of 5–10% was obtained. Inheritance of the transgenes has remained stable over more than 15 generations despite the presence of endogenous piggyBac sequences in the B. tryoni genome. The sequence of insertion sites shows the usual canonical pattern of piggyBac integraton into TTAA target sites. An investigation of endogenous piggyBac elements in the B. tryoni genome reveals the presence of sequences almost identical to those reported recently for the B. dorsalis complex of fruit flies and two noctuid moths, suggesting a common origin of piggyBac sequences in these species. The availability of transformation protocols for B. tryoni has the potential to deliver improvements in the performance of the Sterile Insect Technique for this pest species.     

Interactions of mating,egg production and death rates in females of the Mediterranean fruit fly,Ceratitis capitata.

Costs of reproduction include costs of producing eggs and of mating itself. In the present study, we made an experimental investigation of costs of reproduction in the Mediterranean fruit fly (medfly, Ceratitis capitata). We demonstrated that virgins live longer than non-virgin females. However, in strong contrast to most findings within the Diptera, non-virginity had no detectable effect on egg production. Therefore the increased longevity of the virgin females cannot be attributed to an increase in egg production in non-virgin females, and instead indicates a cost of mating. A comparison of the life spans of normal females and those sterilized by low doses of X-irradiation, revealed an additional cost of egg production. There were no significant differences in remating levels between females that did and did not lay eggs, showing that the cost of producing eggs is independent of mating frequency. Medfly females therefore suffer a decrease in survival as a result of egg production and of mating, and these costs are independent of one another. To put our results into context, we reviewed the existing literature on the effects of mating on longevity, egg production and sexual receptivity for 64 species of Diptera, and examined the pattern of mating effects that emerged.     

Revised irradiation doses to control melon fly, Mediterranean fruit fly, and oriental fruit fly (Diptera: Tephritidae) and a generic dose for tephritid fruit flies

Currently approved irradiation quarantine treatment doses for Bactrocera cucurbitae (Coquillet), melon fly; Ceratitis capitata (Wiedemann), Mediterranean fruit fly; and Bactrocera dorsalis (Hendel), oriental fruit fly, infesting fruits and vegetables for export from Hawaii to the continental United States are 210, 225, and 250 Gy, respectively. Irradiation studies were initiated to determine whether these doses could be reduced to lower treatment costs, minimize any adverse effects on quality, and support a proposed generic irradiation dose of 150 Gy for fruit flies. Dose-response tests were conducted with late third instars of wild and laboratory strains of the three fruit fly species, both in diet and in fruit. After x-ray irradiation treatment, data were taken on adult emergence, and adult female fecundity and fertility. Melon fly was the most tolerant of the three species to irradiation, and oriental fruit fly was more tolerant than Mediterranean fruit fly. Laboratory and wild strains of each species were equally tolerant of irradiation, and larvae were more tolerant when irradiated in fruit compared with artificial diet. An irradiation dose of 150 Gy applied to 93,666 melon fly late third instars in papayas resulted in no survival to the adult stage, indicating that this dose is sufficient to provide quarantine security. Irradiation doses of 100 and 125 Gy applied to 31,920 Mediterranean fruit fly and 55,743 oriental fruit fly late third instars, respectively, also resulted in no survival to the adult stage. Results support a proposed generic irradiation quarantine treatment dose of 150 Gy for all tephritid fruit flies.