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.     

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.     

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.     

Effects of fruit fly host, fruit species, and host egg to female parasitoid ratio on the laboratory rearing of Biosteres arisanus

The host suitability of the oriental fruit fly, Bactrocera dorsalis (Hendel), for development of Biosteres arisanus (Sonan), a braconid parasitoid, was compared with three other fruit fly species, namely, Mediterranean fruit fly, Ceratitis capitata Weidemann, melon fly, Bactrocera cucurbitae Coquilett, and Malaysian fruit fly, Bactrocera latifrons (Hendel). In addition, effects of five different fruit species, namely, Carica papaya L. (solo papaya), Musa sapientum (L.) O. Ktze. (apple banana), Mangifera indica (L.) (Haden mango), Terminalia catappa (L.) (false kamani), and Citrus aurantiifolia (Christman) Swingle (common lime), on the parasitization rate of B. dorsalis and sex ratio of parasitoid progenies were evaluated. Effects of host egg to female B. arisanus ratios on parasitoid progeny yields were likewise determined. The host suitability of fruit flies for development of B. arisanus was ranked as: B. dorsalis>C. capitata=B. latifrons=B. cucurbitae. Based on percent parasitization of B. dorsalis, preference of B. arisanus females for host eggs varied with fruit species, however, preferential oviposition displayed by female parasitoids did not influence sex ratios of subsequent parasitoid progenies. Increases in host egg to female parasitoid ratios of 5:1, 10:1, 20:1, 25:1, and 30:1 corresponded with increases in parasitoid progeny yield reaching a plateau at 20:1.     

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.     

The mating system of the true fruit fly Bactrocera tryoni and its sister species,Bactrocera neohumeralis

The frugivorous “true” fruit fly, Bactrocera tryoni (Queensland fruit fly), is presumed to have a nonresourced‐based lek mating system. This is largely untested, and contrary data exists to suggest Bactrocera tryoni may have a resource‐based mating system focused on fruiting host plants. We tested the mating system of Bactrocera tryoni, and its close sibling Bactrocera neohumeralis, in large field cages using laboratory reared flies. We used observational experiments that allowed us to determine if: (i) mating pairs were aggregated or nonaggregated; (ii) mating system was resource or nonresource based; (iii) flies utilized possible landmarks (tall trees over short) as mate‐rendezvous sites; and (iv) males called females from male‐dominated leks. We recorded nearly 250 Bactrocera tryoni mating pairs across all experiments, revealing that: (i) mating pairs were aggregated; (ii) mating nearly always occurred in tall trees over short; (iii) mating was nonresource based; and (iv) that males and females arrived at the mate‐rendezvous site together with no evidence that males preceded females. Bactrocera neohumeralis copulations were much more infrequent (only 30 mating pairs in total), but for those pairs there was a similar preference for tall trees and no evidence of a resource‐based mating system. Some aspects of Bactrocera tryoni mating behavior align with theoretical expectations of a lekking system, but others do not. Until evidence for unequivocal female choice can be provided (as predicted under a true lek), the mating system of Bactrocera tryoni is best described as a nonresource based, aggregation system for which we also have evidence that land‐marking may be involved.     

Impact of habitat modification on the distribution and abundance of fruit flies (Diptera: Tephritidae) in Southeast Queensland

Loss of rainforest because of agricultural and urban development may impact the abundance and diversity of species that are rainforest natives. Tropical fruit flies are one group of such organisms indigenous to rainforests. In southeast Queensland, a region subject to rapid urbanization, we assessed the impact of habitat disturbance on the distribution and abundance of native fruit flies. Data on four species (Bactrocera tryoni, Bactrocera neohumeralis, Bactrocera chorista, and Dacus aequalis) were gathered and analyzed over 6 months in three habitat types: suburbia, open sclerophyll forest, and rainforest. We also analyzed the data at a combined "dacine fruit fly" level incorporating all fruit fly species trapped over the period of study (as might occur in a biodiversity assessment): these included the four species already named and Bactrocera melas, Bactrocera bryoniae, Bactrocera newmani, and Dacus absonifacies. Analysis at the species level showed that the polyphagous pest species responded differently to the monophagous species. Bactrocera tryoni, which has more exotic than native hosts, was positively affected by transformation of natural habitat into suburbia whereas B. neohumeralis, which has nearly identical numbers of native and exotic hosts, was found equally across habitat types. Bactrocera chorista and Dacus aequalis, each monophagous on a species-specific rainforest host plant, were most abundant in rainforest. The analysis based on the combined data suggests that replacing rainforest with suburbia has a neutral, or even positive, effect on the abundance of fruit flies as a whole. At the species level, however, it can be seen that this is an erroneous conclusion biased by the abundance of a single pest species. Our discussion raises the issue of analyses at supraspecific levels in biodiversity and impact assessment studies. Received: March 6, 2000 / Accepted: June 19, 2000     

蝇蛹俑小蜂对寄主及果实的趋性反应

【背景】蝇蛹俑小蜂是实蝇类害虫蛹期重要的寄生蜂之一。有关植物果实和寄主挥发物在蝇蛹俑小蜂寻找寄主过程中的作用尚不明确。【方法】采用"Y"型嗅觉仪测试了寄主和果实(健康果实和虫害诱导果实)对蝇蛹俑小蜂的引诱作用。【结果】虫伤1 d的番石榴和杨桃果实对蝇蛹佣小蜂雌蜂具有显著的引诱作用;寄主蛹——3日龄橘小实蝇蛹和4日龄瓜实蝇蛹对蝇蛹俑小蜂雌蜂也具有显著的引诱作用。蝇蛹俑小蜂雌蜂对雄蜂有显著的吸引作用。橘小实蝇性诱剂甲基丁香酚对蝇蛹俑小蜂的搜索行为则无显著影响。【结论与意义】寄主蛹和幼虫危害1 d的果实能释放对蝇蛹俑小蜂有引诱作用的物质,这可为利用蝇蛹俑小蜂防治实蝇类害虫提供基础信息。     

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.     

From laboratory to the field: consistent effects of experience on host location by the fruit fly parasitoid Diachasmimorpha kraussii (Hymenoptera: Braconidae)

Associative learning is well documented in Hymenopteran parasitoids, where it is thought to be an adaptive mechanism for increasing successful host location in complex environments. Based on this learning capacity, it has been suggested that providing prerelease training to parasitoids reared for inundative release may lead to a subsequent increase in their efficacy as biological control agents. Using the fruit fly parasitoid Diachasmimorpha krausii we tested this hypothesis in a series of associative learning experiments which involved the parasitoid, two host fruits (tomatoes and nectarine), and one host fly (Bactrocera ttyoni). In sequential Y-tube olfactometer studies, large field-cage studies, and then open field studies, naive wasps showed a consistent preference for nectarines over tomatoes. The preference for nectarines was retained, but not significantly increased, for wasps which had prior training exposure to nectarines. However, and again consistently at all three spatial scales, prior experience on tomatoes led to significantly increased attraction to this fruit by tomato-trained wasps, including those liberated freely in the environment. These results, showing consistency of learning at multiple spatial scales, gives confidence to the many laboratory-based learning studies which are extrapolated to the field without testing. The experiment also provides direct experimental support for the proposed practice of enhancing the quality of inundatively released parasitoids through associative learning.     

Predation potential of the earwig Euborellia annulipes on fruit fly larvae and trophic interactions with the parasitoid Diachasmimorpha longicaudata

The earwig Euborellia annulipes (Lucas) (Dermaptera: Anisolabididae), a generalist predator, has been observed in fruits infested with fruit fly larvae, which are frequently parasitized by parasitoid wasps. Neither the capacity of earwigs to predate on fruit flies nor intraguild interactions between earwigs and fruit fly parasitoids have been investigated. Here, we studied in laboratory conditions the predation on the fruit fly Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) by the earwig E. annulipes, and whether parasitism of fruit fly larvae by the parasitoid wasp Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) influences predation by the earwig. We evaluated the predation capacity, functional response and prey preference of E. annulipes for parasitized and non-parasitized fruit fly larvae in choice and no-choice tests. We found that earwigs prey on second- and third-instar larvae and pupae of C. capitata and consumed larger numbers of second-instar larvae, followed by third-instar larvae and pupae. Females prey on larger numbers of fruit flies than did males, regardless of the prey developmental stage, but both sexes exhibited a type II functional response. Interestingly, males killed but did not consume fruit fly larvae more than did females. In no-choice tests, earwig females consumed equal numbers of parasitized and non-parasitized fruit fly larvae. However, in choice tests, the females avoided feeding on parasitized larvae. Subsequent tests with hexane-washed parasitized and non-parasitized larvae showed that putative chemical markings left on fruit flies by parasitoids did not drive the earwig preference towards non-parasitized larvae. These findings suggest that E. annulipes is a potential biological control agent for C. capitata, and that, because the earwig avoids consuming larvae parasitized by D. longicaudata, a combination of the two natural enemies could have an additive effect on pest mortality.     

Behavioural responses of female Queensland fruit fly, Bactrocera tryoni, to mineral oil deposits

Behavioural responses of Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), females to fruit dipped in water and fruit dipped in 0.5% (vol/vol) aqueous emulsions of a mineral oil were determined and analysed. The mineral oil was an nC20–22 distillation fraction of the base oil used to produce an nC23 horticultural mineral oil. Females caged with oil‐treated fruit had significantly longer prelanding intervals than females caged with water‐dipped fruit. The latter was attacked immediately or shortly after being caged with flies whereas some oil‐dipped fruit was not attacked within 180 min. The percentage of landings that led to oviposition on water‐ and oil‐treated fruit were 58 and 13%, respectively, and the percentages ovipositing after probing were 74 and 25%, respectively. Likewise, average times spent probing were 7 vs. 31 s whereas average times spent ovipositing were 321 vs. 223 s. Females spent less than half as much time on oil‐treated fruit than on water‐treated fruit. Transition probabilities of rejection, when applied to the behaviour sequence indicated that oil‐treated fruits are about nine times less likely to be infested with B. tryoni.     

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.     

Insect oviposition plasticity in response to host availability: the case of the tephritid fruit fly Bactrocera dorsalis

1. Insect oviposition behaviour is ecologically and physiologically plastic. For tephritid fruit flies, Bactrocera dorsalis Hendel, host availability varies spatially and temporally. Females are expected to adopt adaptive oviposition strategies to maximise lifetime reproductive fitness, including survival. Bactrocera dorsalis oviposition tactics in response to different host availabilities were investigated. 2. This study includes three treatments: (i) variable host densities (host density varied according to a fixed cycle from day to day over values of 1, 5, 10 and 20 hosts per cage), (ii) a fixed high host density (20 hosts per cage), and (iii) a fixed low host density (1 host per cage). 3. Daily egg‐laying number per female over the course of 27 days was entirely independent of host density and highly dependent on female age. As host availability increased, females accepted significantly more hosts, generally laid small egg clutches, and more broadly distributed the eggs. 4. Tephritid fruit flies adaptively adjusted egg clutches in ways that reflected the variability of host availability. Egg‐ and time‐limitation constraints appeared to drive these adjustments. Female egg maturation was triggered by oviposition activity and reflected marked lifetime trade‐offs. Such strategies involved specific time schedules for egg laying. 5.This study defined the oviposition plasticity of the tephritid fruit fly. These results have general implications for the behavioural ecology of insect herbivores and parasitoids.     

Susceptibility of low-chill blueberry cultivars to Mediterranean fruit fly, oriental fruit fly, and melon fly (Diptera: Tephritidae)

No-choice tests were conducted to determine whether fruit of southern highbush blueberry, Vaccinium corymbosum L., hybrids are hosts for three invasive tephritid fruit flies in Hawaii. Fruit of various blueberry cultivars was exposed to gravid female flies of Bactrocera dorsalis Hendel (oriental fruit fly), Ceratitis capitata (Wiedemann) (Mediterranean fruit fly), or Bactrocera cucurbitae Coquillet (melon fly) in screen cages outdoors for 6 h and then held on sand in the laboratory for 2 wk for pupal development and adult emergence. Each of the 15 blueberry cultivars tested were infested by oriental fruit fly and Mediterranean fruit fly, confirming that these fruit flies will oviposit on blueberry fruit and that blueberry is a suitable host for fly development. However, there was significant cultivar variation in susceptibility to fruit fly infestation. For oriental fruit fly, 'Sapphire' fruit produced an average of 1.42 puparia per g, twice as high as that of the next most susceptible cultivar 'Emerald' (0.70 puparia per g). 'Legacy', 'Biloxi', and 'Spring High' were least susceptible to infestation, producing only 0.20-0.25 oriental fruit fly puparia per g of fruit. For Mediterranean fruit fly, 'Blue Crisp' produced 0.50 puparia per g of fruit, whereas 'Sharpblue' produced only 0.03 puparia per g of fruit. Blueberry was a marginal host for melon fly. This information will aid in development of pest management recommendations for blueberry cultivars as planting of low-chill cultivars expands to areas with subtropical and tropical fruit flies. Planting of fruit fly resistant cultivars may result in lower infestation levels and less crop loss.     

Temperature effects on “overwintering” phenology of a polyphagous,tropical fruit fly (Tephritidae) at the subtropical/temperate interface

Around the world, several pest tephritids are extending their ranges from warm tropical or Mediterranean climates into cooler temperate regions. The ability to tolerate climatic diversity is uncommon among insects, and understanding the population phenology drivers of such species across different parts of their range will be critical for their management. Here, we determined the role of temperature versus fruit availability on the population phenology of Queensland fruit fly, Bactrocera tryoni. Using a field site located at the subtropical/temperate interface, with host fruits continuously available, we monitored the development times and abundance of B. tryoni, a species which has invaded temperate Australia from the tropics. From fruit samples held at ambient and controlled conditions, the abundance of emerging flies was highly variable among collection dates, but the variance did not reflect the observed changes in temperature. For most samples, the survival rate of flies in a field site was lower than predicted by a day‐degree population model fitted with mean daily field temperatures. The development time of the immature stage in the field was prolonged, presumably due to cooler ambient conditions, but the fitted day‐degree population model consistently over‐predicted estimated development times. Our results indicate that at the subtropical/temperate interface, the decline in B. tryoni populations during winter is only partly driven by temperature and host availability. We classify B. tryoni as a climate generalist, which likely employs physiological as well as behavioural mechanisms to achieve broad climatic tolerance ranges.     

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 evaluation of two olive fruit fly parasitoids under varying abiotic conditions

Psyttalia lounsburyi (Silvestri) and P. humilis (Silvestri) (Hymenoptera: Braconidae) were evaluated in California for their potential to control the invasive olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae). Psyttalia lounsburyi is a specialist on B. oleae while P. humilis also attacks other tephritid species. Field cage trials, conducted from 2006 to 2009, were used to compare P. lounsburyi and two populations of P. humilis (Kenya and Namibia) in California’s interior valley and coastal regions. Both parasitoid species reproduced on B. oleae in all trials. Under similar abiotic conditions, offspring production per female was higher in P. humilis than in P. lounsburyi, suggesting that host specificity by P. lounsburyi does not confer a higher efficiency on B. oleae in cultivated olives. Two abiotic factors were shown to impact parasitoid efficiency. First, adult parasitoid survival was poor during periods of high summer temperatures, common to the olive production areas in California’s interior valleys. Second, parasitism levels were lower on B. oleae larvae feeding in larger Ascolano cv. fruit than in smaller Manzanillo cv. fruit. Results are discussed relative to biological control of B. oleae in commercial olives and the usefulness of natural enemies specialized to attack fruit flies in wild olives compared with the larger cultivated olive fruit.     

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.     

Simultaneous tests of the preference-performance and phylogenetic conservatism hypotheses: is either theory useful?

The preference-performance and phylogenetic conservatism hypotheses have been postulated to explain the mechanisms driving host-use patterns of phytophagous insects. The preference-performance hypothesis predicts that insects will use plants that provide higher offspring fitness, while the phylogenetic conservatism hypothesis predicts that insects will use phylogenetically closely related plants over more distantly related plants. Although some studies have supported these two hypotheses, others have not. Simultaneous tests of the two hypotheses on more than one species are lacking, and this limits comparative interpretation of previous studies. We undertook a comparative investigation to determine whether preference-performance and/or the phylogenetic conservatism hypothesis can explain host-use patterns of two phytophagous insects, the fruit flies Bactrocera cucumis and B. tryoni. Within a nested, plant phylogenetic framework, oviposition preference and offspring performance of the two fruit fly species were tested on fruits of plant species from across different plant families, from within a family and across cultivars within a species. The results show that both the preference-performance and the phylogenetic conservatism hypotheses can, depending on the host plant taxonomic level, explain host usage patterns in B. cucumis, while neither theory explained the host patterns seen in B. tryoni. In the light of increasing recognition of the complexity of host plant–herbivore relationships, and of ongoing studies which as often as not fail to find support for these theories as those that do, we discuss the limited value of either theory as a basis for future research.