Variation in ovariole number and egg size of species of Dacus (Diptera; Tephritidae) and their relation to host specialization

Abstract. 1. An analysis of the number of ovarioles/ovary is presented for fourteen species of Dacus ranging from broad generalists (D.tryoni (Frogg.)) to strict host specialists (D.aglaia Hardy). For eight species data on egg size and the incubation time of eggs is also presented. Interrelationships among these life history variables and their relationships to host specialization were examined. 2. There was a broad positive relationship between the breadth of the natural host range (i.e. excluding cultivated fruits) and ovariole number (and hence potential fecundity). Highly polyphagous species had thirty-five to forty ovarioles/ovary while the specialists ranged from eight to twenty. 3. D.musae (Tryon), a specialist on banana, was an exception having an ovariole number similar to that of the most polyphagous species. 4. There was no clear relationship between egg size and ovariole number across eight species, though monophages were not fully represented in this analysis. Among these eight species there was no significant relationship between wing length and egg length, nor was there any such relationship among individuals within species. 5. There was considerable variation among species in the incubation time (at 25°C) for eggs, ranging from 24 h for D.cucumis French to 53 h for D.cacuminatus (Hering). This variation was only weakly related to egg size, though D.cucumis produced the largest eggs of any species examined. 6. Possible explanations for a relationship between potential fecundity and host range are discussed in terms of the balance between the abundance of host resources for generalists and their predictability for specialists. However, the observed relationship between ovariole number and host range must remain tentative, given that only fourteen species from one genus have been examined. Considerably more data is required for other dacines, for species in other tephritid subfamilies, and for other phytophagous insect groups to determine whether the relationship is generally applicable.     

The influence of a shortage of hosts on the specificity of oviposition behaviour in species of Dacus (Diptera, Tephritidae)

ABSTRACT. When deprived of their preferred hosts for up to 16 days prior to behaviour assays, three relatively specialized tephritid flies, D. cacuminatus (Hering), D. cucumis French and D. jarvisi (Tryon), retain strong preferences for their particular hosts. Moreover, in the absence of the preferred hosts, D. cacuminatus , and to a lesser extent D. cucumis , will not accept fruits that are outside their normal host range. D. jarvisi readily accepts other fruits in the absence of its preferred host, Planchonia careya , but in common with the other two shows no increase in the number of eggs laid with increasing periods of deprivation. None of these species accumulate oocytes when deprived of fruits.
In contrast, the highly polyphagous D. tryoni Frogg. lays more eggs and oviposits readily into a previously unacceptable fruit after 4 days without access to hosts. This change in behaviour is associated with a marked increase in the number of mature eggs carried by females.
These results suggest an important difference between the generalist and more specialized species in the physiological control of oocyte maturation. In D. tryoni there appears to be no inhibition of oocyte development once the primary follicle has matured, whereas in the other species each ovariole contains no more than one mature egg.
In D. tryoni , the change in behaviour which accompanies this increase in egg load, may influence its propensity to accept unusual fruits, and may help to explain its rapid acceptance of most cultivated fruits introduced to Australia.     

Oviposition behaviour of two tephritid fruit flies,Dacus tryoni and Dacus jarvisi,as influenced by the presence of larvae in the host fruit

Summary When offered a choice, females of the fruit flies Dacus tryoni (Frogg.) and D. jarvisi (Tryon) strongly preferred to lay in fruits without larvae rather than fruits which already contained larvae. Fruits which contained even low densities of larvae, including newly hatched ones, received many fewer eggs than control fruits. This preference was not influenced by the species of larvae present in the fruits nor by the distance to uninfested fruits. Discrimination occurred when fruits with and without larvae were close together (10 cm apart) and also when they were separated by distances of about one metre. Laboratory assays suggested that the flies detect chemical changes in the fruit associated with the decomposition which accompanies larval feeding, but they do not seem to detect the larvae Perse. This behaviour may be significant when these two species utilise the same host since the species which is able to infest fruits first will reduce the availability of hosts for the other species. In contrast to many other Tephritids (e.g. Rhagoletis, Anastrepha and Ceratitis) female Dacus don't discriminate against fruits which contain eggs nor do they deposit a pheromone to deter oviposition by females that subsequently visit the fruit. An hypothesis is proposed to explain the absence of oviposition-deterring pheromones in Dacus, and their presence in many other species of Tephritidae, on the basis of differences in life history and population structure.     

Intra- and interspecific competition by Fopius arisanus and Diachasmimorpha tryoni (Hymenoptera: Braconidae), parasitoids of tephritid fruit flies

Fopius arisanus (Sonan) and Diachasmimorpha tryoni (Cameron) are two important solitary endoparasitoids of tephritid fruit flies. The former species attacks host eggs while the latter attacks host larvae, and both species emerge as adults from the host puparium. This study investigated intrinsic competition between these two parasitoids, as well as aspects of intraspecific competition within each species in the Mediterranean fruit fly, Ceratitis capitata (Wiedemann). Parasitization by F. arisanus resulted in direct mortality of host eggs and prolonged development of host eggs and larvae. Superparasitism by F. arisanus was uncommon when mean parasitism per host patch was <50%, but increased with rising rates of parasitism. Superparasitism by D. tryoni was more common. In superparasitized hosts, supernumerary individuals of F. arisanus were killed through physiological suppression, while supernumerary larvae of D. tryoni were killed mainly through physical attack. In multiparasitized hosts, dissections showed that 81.6% of D. tryoni eggs in the presence of F. arisanus larvae died within 3 days, indicating physiological inhibition of egg hatch. Rearing results further showed that F. arisanus won almost all competitions against D. tryoni. The ratio of D. tryoni stings to ovipositions was lower in hosts not previously parasitized by F. arisanus than in parasitized hosts, suggesting that D. tryoni can discriminate against parasitized hosts. The mechanism that F. arisanus employs to eliminate D. tryoni is similar to that it uses against all other larval fruit fly parasitoids so far reported. The results are discussed in relation to the competitive superiority of early acting species in fruit fly parasitoids, and to a possible competitive-mediated mechanism underlying host shift by D. tryoni to attack non-target flies following the successful introduction of F. arisanus in Hawaii.     

An improved culturing method for opiine fruit fly parasitoids and its application to parasitoid monitoring in the field

Good culturing methods play an important role in the study of insect behavior and its application to pest management. Here, we describe and validate a new method for rearing the parasitoid wasp, Diachasmimorpha kraussii, which attacks some of the world's worst fruit fly pests and is an internationally used biological control agent. Our method differs from standard culturing approaches by presenting adult wasps with host‐infested artificial media within a “culturing bag,” which mimics a natural (fruit) oviposition substrate. In laboratory trials using wild collected D. kraussii, the culturing bag method was compared to the use of host‐infested nectarines, and a commonly used laboratory method of presenting host‐infested artificial media within Petri dishes. The culturing bag method proved to be a significant improvement on both methods, combining the advantages of high host survival in artificial media with parasitism levels that were the equivalent to those recorded using host‐infested fruits. In our field study, culturing bags infested with the Queensland fruit fly, Bactrocera tryoni, and hung in a mixed peach and nectarine orchard proved to be effective “artificial fruits” attracting wild D. kraussii for oviposition. Significantly more adult wasps were reared from the culturing bags compared to field collected fruits. This was shown to be due to higher fruit fly larval density in the bags, as similar percentage parasitism rates were found between the culturing bags and ripe fruits. We discuss how this cheap, time‐efficient method could be applied to collecting and monitoring wild D. kraussii populations in orchards, and assist in maintaining genetic variability in parasitoid laboratory cultures.     

Bacteria associated with four species of Dacus (Diptera: Tephritidae) and their role in the nutrition of the larvae

Summary The bacteria associated with Dacus tryoni (Froggatt), Dacus jarvisi (Tryon), Dacus neohumeralis (Hardy) and Dacus cacuminatus (Hering) were examined. Bacteria were isolated from the surface of freshly-laid eggs, from within surface sterilised pupae, from heads and abdomens of wild and laboratory-maintained flies, and from decomposed fruits in which the wild larvae were feeding. A more diverse flora was associated with D. tryoni and D. jarvisi (15 and 14 species, respectively) than with D. neohumeralis and D. cacuminatus (9 and 6 species, respectively). Most of the bacteria belonged to the family Enterobacteriaceae and while there were similarities of bacterial associations between fly species there was no evidence of a strict symbiotic association of a particular bacterium or bacteria with each species of fly. The larvae of D. jarvisi were unable to develop normally in an artificial medium containing unhydrolysed protein and free of bacteria and on a medium containing casein and Serratia liquefaciens (isolated from the flies and shown to secrete protease) the larvae died. On the same casein medium containing Enterobacter cloacae (isolated from the flies and shown to be protease negative) the larvae developed normally. Larvae of D. tryoni and D. jarvisi were devoid of protease and cellulase activity, but contained some amylase activity. The significance of these results in terms of current hypotheses concerning symbioses between tephritids and bacteria is discussed.     

Opiine parasitoids (Hymenoptera: Braconidae) and biological control of fruit flies (Diptera: Tephritidae) in Australia: Past,present and future

Opiine braconids are parasitoids of the immature stages of frugivorous tephritids. The female wasp lays her eggs into the eggs or larvae of the fruit fly host, where the immature wasp develops before emerging as a next-generation adult from the now dead host pupal case. In support of a new generation of Australian fruit fly parasitoid research, this paper comprehensively reviews what is known about the Australian fruit fly infesting opiines. Based on the most recent taxonomic revision 11 fruit fly infesting opiine species are documented to occur in Australia, but we consider as doubtful the record for Diachasmimorpha longicaudata and consider the record for Fopius illusorius to be tentative without further collections. We identify that the systematics and taxonomy of the Australian native fruit fly infesting opiines are in urgent need of further work. The history of fruit fly biological control in Australia is comprehensively reviewed, including the export of native Australian opiines for fruit fly control elsewhere in the world. Australia was actively involved in three major classical biological control programmes against fruit flies from the turn of the 1900s until the mid-1960s. Despite the introduction of 11 opiine species, plus numerous other natural enemies, only Fopius arisanus established in eastern Australia, where in South-east Queensland it can now cause between 30 and 40% mean parasitism. In addition to the exotic F. arisanus, the native species Diachasmimorpha kraussii and Diachasmimorpha tryoni also cause fruit fly parasitism in agriculturally important crops: both species have also been liberated widely outside of Australia for fruit fly control. Other Australian opiines have not been reared from flies infesting commercial crops and appear biologically restricted to the fruits and environs of Australian east-coast rainforests. The biology literature for D. tryoni and D. kraussii is comprehensively reviewed, while for F. arisanus, already reviewed elsewhere, key literature only is covered. Forward looking, we consider the potential for inoculative or inundative releases of opiines in areas where they do not currently occur to be good, while conservation biological control may help to increase the impacts of parasitoids in areas where they are already established.     

Host location by the fruit fly parasitoid Diachasmimorpha krausii: role of fruit fly species,life stage and host plant

• 1 Diachasmimorpha krausii is a braconid parasitoid of larval tephritid fruit flies, which feed cryptically within host fruit. At the ovipositor probing stage, the wasp cannot discriminate between hosts that are physiologically suitable or unsuitable for offspring development and must use other cues to locate suitable hosts.
• 2 To identify the cues used by the parasitoid to find suitable hosts, we offered, to free flying wasps, different combinations of three fruit fly species (Bactrocera tryoni, Bactrocera cacuminata, Bactrocera cucumis), different life stages of those flies (adults and larvae) and different host plants (Solanum lycopersicon, Solanum mauritianum, Cucurbita pepo). In the laboratory, the wasp will readily oviposit into larvae of all three flies but successfully develops only in B. tryoni. Bactrocera tryoni commonly infests S. lycopersicon (tomato), rarely S. mauritianum (wild tobacco) but never C. pepo (zucchini). The latter two plant species are common hosts for B. cacuminata and B. cucumis, respectively.
• 3 The parasitoid showed little or no response to uninfested plants of any of the test species. The presence of adult B. tryoni, however, increased parasitoid residency time on uninfested tomato.
• 4 When the three fruit types were all infested with larvae, parasitoid response was strongest to tomato, regardless of whether the larvae were physiologically suitable or unsuitable for offspring development. By contrast, zucchini was rarely visited by the wasp, even when infested with B. tryoni larvae.
• 5 Wild tobacco was infrequently visited when infested with B. cacuminata larvae but was more frequently visited, with greater parasitoid residency time and probing, when adult flies (either B. cacuminata or B. tryoni) were also present.
• 6 We conclude that herbivore‐induced, nonspecific host fruit wound volatiles were the major cue used by foraging D. krausii. Although positive orientation to infested host plants is well known from previous studies on opiine braconids, the failure of the wasp to orientate to some plants even when infested with physiologically suitable larvae, and the secondary role played by adult fruit flies in wasp host searching, are newly‐identified mechanisms that may aid parasitoid host location in environments where both physiologically suitable and unsuitable hosts occur.

     

Biological attributes of three introduced parasitoids as natural enemies of fruit flies,genus Anastrepha (Diptera: Tephritidae)

The biological attributes of three introduced species of parasitoids which attack the fruit fly Anastrepha ludens were evaluated. Larvae and eggs of A. ludens were exposed to larval parasitoids Diachasmimorpha longicaudata and D. tryoni and the egg parasitoid Fopius arisanus. Parasitoid longevity and fecundity were determined using larvae and eggs of A. ludens. Likewise, the parasitism rates of these parasitoid species in infested host fruits were recorded. The intrinsic rate of increase for F. arisanus was 0.1019 followed by D. tryoni with a rate of 0.1641 and D. longicaudata with the highest rate of 0.2233. Although F. arisanus females had the highest levels of fecundity, only 50% of them remained alive until reproductive age. These results in combination with the longer generation time (in comparison with D. longicaudata and D. tryoni), can be considered as the most important factors explaining F. arisanus reduced rate of increase. However, we note that oviposition activity caused egg mortality which reduced Anastrepha egg hatch by ca. 20%. This result suggests that F. arisanus has a high potential as a natural enemy of A. ludens, in accordance with our research efforts to develop a new F. arisanus strain specialized for development in Anastrepha eggs. The results show that D. tryoni is not a good candidate for biological control of Anastrepha. Meanwhile, D. longicaudata continues to be the most important exotic parasitoid for suppression of Anastrepha fruit fly populations.     

Are insect frugivores always plant pests? The impact of fruit fly (Diptera: Tephritidae) larvae on host plant fitness

Herbivory is generally regarded as negatively impacting on host plant fitness. Frugivorous insects, which feed directly on plant reproductive tissues, are predicted to be particularly damaging to hosts. We tested this prediction with the fruit fly, Bactrocera tryoni, by recording the impact of larval feeding on two direct (seed number and germination) and two indirect (fruit decay rate and attraction/deterrence of vertebrate frugivores) measures of host plant fitness. Experiments were done in the laboratory, glasshouse and tropical rainforest. We found no negative impact of larval feeding on seed number or germination for three test plants: tomato, capsicum and eggplant. Further, larval feeding accelerated the initiation of decay and increased the final level of fruit decay in tomatoes, apples, pawpaw and pear, a result considered to be beneficial to the fruit. In rainforest studies, native rodents preferred infested apple and pears compared to uninfested control fruit; however, there were no differences observed between treatments for tomato and pawpaw. For our study fruits, these results demonstrate that fruit fly larval infestation has neutral or beneficial impacts on the host plant, an outcome which may be largely influenced by the physical properties of the host. These results may contribute to explaining why fruit flies have not evolved the same level of host specialization generally observed for other herbivore groups.     

Effects of origin and experience on patterns of host acceptance by the opiine parasitoid Diachasmimorpha tryoni

1. Patterns of host acceptance by Diachasmimorpha tryoni (Ashmead), a parasitoid of tephritid flies, were evaluated in relation to host–substrate complex, wasp origin, and wasp experience. 2. Naive female D. tryoni originating both from the Mediterranean fruit fly (medfly) Ceratitis capitata (Wiedemann) and the lantana gall fly Eutreta xanthochaeta Aldrich probed medfly-infested coffee fruit two to six times more often than E. xanthochaeta-inhabited lantana galls. No significant differences were detected between the two groups of parasitoids in patterns of probing response to medfly-infested coffee fruit or to E. xanthochaeta galls. 3. An 18-h pretest exposure to medfly-infested coffee fruit or E. xanthochaeta-inhabited galls affected the probing response of D. tryoni to E. xanthochaeta galls significantly, but did not affect the probing response to medfly-infested coffee fruit. Diachasmimorpha tryoni exposed to E. xanthochaeta galls probed E. xanthochaeta galls two to three times more often than naive wasps, and seven to 11 times more than wasps exposed to medfly-infested coffee fruit. Regardless of the prior exposure treatments, a high proportion (75–100%) of the test parasitoids probed medfly-infested coffee fruit. 4. Parasitoid acceptance of less-preferred hosts or host–substrate complexes may be more amenable to conditioning through prior experience (i.e. learning) than preferred host–substrate complexes. The relevance of these findings to host range expansion of parasitoids used in fruit fly biological control is discussed.     

Effect of Diachasmimorpha tryoni on two non-target flowerhead-feedingtephritids

Laboratory tests were conducted to evaluate the possible effect of a deliberately introduced fruit fly parasitoid, Diachasmimorpha tryoni, on 2 non-target flowerhead-feeding tephritid flies,Trupanea dubautiae and Ensina sonchi. The former is an nativecomposite endemic Hawaiian tephritid which feeds on flowerheads of the native composite shrub, Dubautia raillar dioides; the latter is an inadvertently introduced tephritid infesting flowerheads of the exotic weed, Sonchus oleraceus. Gravid females of D. tryoniwere confined in test cages with field-collected D.raillardioides and S. oleraceus flowerheads infested with late instars of T. dubautiae and E. sonchi,respectively. D. tryoni showed low levels of visiting and probing responses to D. raillardioides flowerheads and relatively higher responses to S. oleraceus flower heads in both the presence and absence of the parasitoid's normal host, the Mediterranean fruit fly, Ceratitis capitata. With 72-h exposure to D. tryoni, 13.9 and 2.6% of T. dubautiaewere attacked by test parasitoids in the absence and presence of C.capitata in the test cage, respectively; while 56.8 and34.2% of E. sonchi were attacked. In contrast, 94.0 and84.0% of C. capitata larvae presented in screened disheswith diet in test cages were attacked by D. tryoni in testswith T. dubautiae and E. sonchi, respectively. Attackof D. tryoni on flowerhead-feeding T. dubautiae andE. sonchi resulted in significant reduction in the emergence ofadult flies, especially in the absence of the parasitoid's normal host.While 8.8–12.8 adult D. tryoni per test (both males andfemales) successfully emerged from medflies, no adult D. tryoniprogeny emerged from T. dubautiae, and only 3 deformed males ofD. tryoni (much smaller than the normal wasp) emerged fromE. sonchi. The relevance of these findings to the safety offuture biological control programs against tephritid pests is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Attraction of fruit flies of the genus Bactrocera to colored mimics of host fruit

In tests on feral populations of polyphagous Bactrocera tryoni (Froggatt) adults on host guava trees, both sexes were significantly more attracted to Tangletrap‐coated 50 mm diameter spheres colored blue or white than to similar spheres colored red, orange, yellow, green, or black or to Tangletrap‐coated 50 mm diameter yellow‐green guava fruit. In contrast, in tests on feral populations of oligophagous Bactrocera cacuminata (Hering) on host wild tobacco plants, both sexes were significantly more attracted to Tangletrap‐coated 15 mm diameter spheres colored orange or yellow than to other colors of spheres or to Tangletrap‐coated 15 mm diameter green wild tobacco fruit. Both sexes of both tephritid species were significantly more attracted to blue (in the case of B. tryoni) or orange (in the case of B. cacuminata) 50 mm spheres displayed singly than to blue or orange 15 mm spheres displayed in clusters, even though fruit of wild tobacco plants are borne in clusters. Finally, B. tryoni adults were significantly less attracted to non‐ultraviolet reflecting bluish fruit‐mimicking spheres than to bluish fruit‐mimicking spheres having a slightly enhanced level of ultraviolet reflectance, similar to the reflectance of possible native host fruit of B. tryoni, whose bluish skin color is overlayed with ultraviolet‐reflecting waxy bloom. Responses to fruit visual stimuli found here are discussed relative to responses found in other tephritid species.     

Competition between Diachasmimorpha kraussii and Fopius arisanus in Bactrocera tryoni: does native parasitoid-host association matter?

In Australia Fopius arisanus (Sonan) is an established, but exotic fruit fly egg-larval-pupal parasitoid which co-occurs with Diachasmimorpha kraussii (Fullaway), a native larval-pupal fruit fly parasitoid: both attack the native fruit fly Bactrocera tryoni (Froggatt). In interactions involving evolutionary novel host-parasitoid associations, F. arisanus consistently out-competes other parasitoid species, including D. kraussii. However, in fruit fly-parasitoid systems where there is co-evolutionary history between parasitoids and their hosts, competitive hierarchies can vary. In this study we investigated the outcome of competition between F. arisanus and D. kraussii within B. tryoni, to test whether the close evolutionary relationship between D. kraussii and B. tryoni might circumvent the competitive advantage of F. arisanus. Consistent with previous research, and despite the evolutionary relationship, dissection of multiparasitized B. tryoni larvae showed that D. kraussii was invariably suppressed by F. arisanus. A total of 47% and 74% of the eggs of D. kraussii in presence of F. arisanus were killed within a span of 24 h and 48–72 h, respectively. However, parasitoid emergence from fruit fly hosts exposed sequentially to F. arsianus and D. kraussii suggest that D. kraussii females are able to discriminate hosts already parasitized by F. arisanus. Results show that the co-evolutionary relationship between B. tryoni and D. kraussii does not help overcome the early-acting advantage of the egg parasitoid F. arisanus. Though F. arisanus may not have completely displaced D. kraussii in its native habitat, simultaneous inundative releases of these two parasitoid species (currently under consideration) might not help increase B. tryoni parasitism levels.

     

Comparative fecundity, clutch size, ovariole number and egg size of Dacus tryoni and D. jarvisi, and their relationship to body size

Dacus tryoni (Frogg.) (Diptera: Tephritidae) is the main tephritid pest of cultivated fruits in Australia. D. jarvisi (Tryon) is also able to infest these fruits. Some factors influencing the rate at which D. tryoni and D. jarvisi exploit patches of host fruits were examined to determine whether one species may have an advantage when they exploit the same fruits in the field. Measurements of the intrinsic rate of increase, ovariole number, clutch size and egg size and the influence of body size on these parameters were made for both species in the laboratory. Up to 10 weeks of age D. tryoni produced twice as many eggs as D. jarvisi, most during a peak 3–5 weeks after adult emergence. The difference in fecundity up to 10 weeks can be explained partly by the higher number of ovarioles in D. tryoni (38/ovary) compared to D. jarvisi (27/ovary). In addition D. tryoni produces smaller eggs than D. jarvisi and distributes them in smaller clutches; 3–4 eggs/clutch vs 10–15. In both species there was a positive correlation between ovariole number and body size (as measured by wing length). By contrast, egg size remained constant over a broad range of body sizes. The influence of these life history differences on the interaction between D. tryoni and D. jarvisi in the field is discussed.

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Résumé D. tryoni Frogg est la principale téphrididae nuisible aux fruits cultivés en Australie. Cependant, plusieurs autres espèces de Dacus, dont D. jarvisi Tryon sont susceptibles de contaminer ces fruits. Quelques facteurs influant sur le taux de contamination de fruits ont été examinés pour déterminer si une espèce peut être avantagée lors de l'exploitation des mêmes fruits dans la nature. L'influence de la taille de l'adulte sur le taux d'accroissement intrinsèque, sur le nombre d'ovarioles, sur l'effectif des pontes et sur la taille des ufs a été examinée au laboratoire sur les 2 espèces. Pendant les 10 premières semaines, D. tryoni produit 2 fois plus d'ufs que D. jarvisi, la plupart étant pondus entre la 3^e et la 5^e semaines après l'émergence. La production de D. tryoni diminue rapidement après ce maximum. D. jarvisi ne présente pas ce maximum précoce, et la production des ufs se fait au même rythme entre les 3^e et 7^e semaines, avant de diminuer graduellement. La différence de fécondité au bout de 10 semaines peut être expliquée partiellement par le plus grand nombre d'ovarioles de D. tryoni (38/ovaire) contre 24/ovaire pour D. jarvisi. De plus, D. tryoni forme des ufs plus petits que D. jarvisi et l'effectif de chacune de ses pontes est plus limité: 3 à 4 ufs contre 10 à 15. Chez les deux espèces, il y a une relation directe nette entre le nombre d'ovarioles et la taille du corps de la femelle (mesurée par la longueur de l'aile). Par contre, la taille des ufs est indépendante d'une grande gamme de tailles du corps des femelles. Les caractéristiques biologiques de D. tryoni le rendent capable de contaminer rapidement les bouquets de fruits qu'il vient de coloniser, ce qui réduit les disponibilités pour les autres espèces susceptibles de contaminer ces fruits. Dans le cas particulier de D. jarvisi, D. tryoni a peu d'impact sur son niveau de population, puisque D. jarvisi peut exploiter aussi son hôte d'origine, Planchonia careya: Il ne tend à entrer en compétition avec D. tryoni que pour une ou deux générations tardives en été, quand l'hôte partage (la goyave) est souvent abondant. Néanmoins, si les fruits sont rares à cette époque ou si les 2 espèces sont obligées de partager leurs hôtes pendant plusieurs générations (hors de l'aire de Planchonia), D. tryoni aura un avantage certain.

     

Evaluation of Diachasmimorpha longicaudata (Hymenoptera: Braconidae) as a mortality factor of Ceratitis capitata (Diptera: Tephritidae) infesting Citrus species under laboratory and field-cage conditions

Ceratitis capitata (or medfly) is one of the major pests currently affecting fruit crops in northwestern Argentinian Citrus-producing areas. Medfly populations are sustained in large exotic fruits, such as Citrus paradisi, Citrus aurantium and Citrus sinensis, which are known to hinder the activity of almost all native parasitoid species. Therefore, a feasible approach to controlling medfly involves the use of exotic parasitoids such as Diachasmimorpha longicaudata. In this study, the prediction that parasitoid females would be proficient at finding medfly larvae infesting the Citrus species mentioned earlier was tested. Particularly, the variation in fruit species preference by parasitoid females, the efficacy of the parasitoid to kill medfly and the effect of host density on parasitoid performance were determined. Parasitoids were allowed to forage for 8 h on grapefruits and oranges artificially infested with medfly larvae under controlled (laboratory) and uncontrolled (field cage) environmental conditions. Fruit choice and no-choice tests were performed. Results were assessed by comparing the number of female visits to and ovipositor insertions into the fruit, and parasitoid emergence, parasitism and additional host mortality percentages. Parasitoid preference for visiting larger fruits (sour orange and grapefruit) may be related to the increased fruit surface area. Ovipositional activity on fruit was influenced by the variation of the larval host density per unit of fruit surface. The higher parasitism rates recorded from sweet orange would be mainly a result of both increased host density and fruit physical features. Nevertheless, D. longicaudata showed the capacity to parasitise hosts in all Citrus species tested.     

Comparative demography of a specialist and generalist fruit fly: Implications for host use and pest management

Host plants used by phytophagous insects can have significant consequences on demography parameters, overall lifetime fitness and their subsequent population dynamics. Here, we conduct a comparative demographic study between the specialist Zeugodacus cucumis (French) and generalist Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) to determine whether the host plants used by these fly species play any role in their overall lifetime fitness and explains current host use patterns. These two fly species are pests within the north-eastern region of Australia and we further aimed to use complete life-history data to determine the population parameters and models that would help identify the sensitive life-history stage that could be targeted for effective field management. Eggs collected from laboratory-reared flies were inoculated into organically grown fruits of both the primary and alternate host plant cultivars of both fly species. The proportion surviving each life stage from egg through to adult and fecundity were monitored for all cohorts from the different plant cultivars. Complete stage-base life-tables for cohorts of each fly species developing from each fruit cultivar were constructed, and the key demographic parameters and population models were analysed using PopTools matrix model programme. Our results showed that the host used by each fly species had significant consequences on fly demographic parameters and hence their overall lifetime fitness. The generalist B. tryoni was able to compensate for the fitness loss experienced at the pre-adult stage by having adults with higher fecundity, but this was not the case for the specialist Z. cucumis. Stage-base population models revealed that the population growth rate of both species was highly sensitive at the adult reproductive stage, indicating that manipulating probability of survival at this life stage would effectively manage populations of these pest species. This study provides the empirical evidence of undertaking complete life history demography studies of phytophagous insects to accurately understand their lifetime fitness consequences of using a certain host, their observed host use patterns, and overall population dynamics. We suggest that any efforts to manage dacine fruit fly pest population should consider life-history consequences of host use.     

Competitive interactions and partial displacement of Anastrepha obliqua by Ceratitis capitata in the occupation of host mangoes (Mangifera indica)

1. We examined the competitive interactions between a native fruit fly species (Anastrepha obliqua Macquart) and the invasive medfly (Ceratitis capitata Wiedemann) when these co-occur on a shared mango fruit host (Mangifera indica L.).
2. Using mango fruits of distinct levels of ripeness, we investigated both competition among larvae and among adult females for oviposition. We quantified competition by the numbers of eggs laid and the intensity of agonistic interactions between adult females.
3. Interactions between immature fruit flies led to reduced size and number of emerged adults of both species. These impacts were felt more acutely in the native species.
4. Interspecific competition between females led to fewer eggs laid on semi-ripe fruit by both species, which may be the result of niche overlap associated with oviposition.
5. Intraspecific interactions between A. obliqua individuals led to intense agonistic behaviour, with a concurrent decrease in number of landings on these host fruits.
6. These results suggest that the native species undergoes a partial niche displacement when facing the invasive species. A portion of the fundamental niche of A. obliqua remained unoccupied by the invading C. capitata, which may allow their coexistence under natural conditions.

     

Preference and performance of Diachasmimorpha kraussii (Fullaway) (Hymenoptera: Braconidae) on five commercial fruit species

Diachasmimorpha kraussii is a polyphagous endoparasitoid of dacine fruit flies. The fruit fly hosts of D. krausii, in turn, attack a wide range of fruits and vegetables. The role that fruits play in host selection behaviour of D. kraussii has not been previously investigated. This study examines fruit preference of D. kraussii through a laboratory choice‐test trial and field fruit sampling. In the laboratory trial, oviposition preference and offspring performance measures (sex ratio, developmental time, body length, hind tibial length) of D. kraussii were investigated with respect to five fruit species [Psidium guajava L. (guava), Prunis persica L. (peach), Malus domestica Borkh. (apple), Pyrus communis L. (pear) and Citrus sinensis L. (orange)], and two fruit fly species (Bactrocera jarvisi and B. tryoni). Diachasmimorpha kraussii responded to infested fruit of all fruit types in both choice and no‐choice tests, but showed stronger preference for guava and peach in the choice tests irrespective of the species of fly larvae within the fruit. The wasp did not respond to uninfested fruit. The offspring performance measures differed in a non‐consistent fashion between the fruit types, but generally wasp offspring performed better in guava, peach and orange. The offspring sex ratio, except for one fruit/fly combination (B. jarvisi in apple), was always female biased. The combined results suggest that of the five fruits tested, guava and peach are the best fruit substrates for D. krausii. Field sampling indicated a non‐random use of available, fruit fly infested fruit by D. kraussii. Fruit fly maggots within two fruit species, Plachonia careya and Terminalia cattappa, had disproportionately higher levels of D. krausii parasitism than would be expected based on the proportion of different infested fruit species sampled, or levels of fruit fly infestation within those fruit.