Interspecific interactions between the gall-fly Urophora affinis Frfld. (Diptera: Tephritidae) and the weevil Larinus minutus Gyll. (Coleoptera: Curculionidae), two biological control agents released against spotted knapweed, Centaurea stobe L. ssp. micranthos

Interspecific competition has been suggested as an explanation for the failure of some insects as biological control agents for weeds. Enclosure and exclusion cages were used, in southern British Columbia, Canada to evaluate the importance of interspecific competition between a seedhead weevil, Larinus minutus, and a gall-inducing fly, Urophora affinis, two biocontrol agents released against spotted knapweed in North America. At the seedhead scale, U. affinis, which is an inferior biological control agent based on knapweed seed mortality, was the superior competitor. Larinus minutus attack rates were significantly lower in the presence of U. affinis compared to release treatments where L. minutus was attacking alone. Reduced L. minutus attack rates were apparent in seed heads expected to contain both species, assuming insect distributions were random, but instead only contained U. affinis. L. minutus did not significantly affect U. affinis density. Although overall attack rates on knapweed seedheads were higher when both species were together at a site, the consequence of the antagonistic interaction is that overall seed destruction was not as high as it could have been if the weevil were attacking on its own. These results support minimizing the number of biocontrol agents released that use similar resources on the target weed, to avoid negative interactions between control agents and potential reductions in biocontrol efficacy resulting from competitive exclusion.     

Influence of Centaurea biebersteinii patch size on Urophora quadrifasciata (Dipt. Tephritidae) in Michigan, USA

Abstract:  Host plant patch size plays an important role in the distribution and densities of many insect species. Understanding how the host plant patch size influences the population of a biological control agent is necessary to monitor the success of a biological control programme. Urophora quadrifasciata (Dipt. Tephritidae) was released in the early 1970s to control the spotted knapweed, Centaurea biebersteinii (Asteraceae) in North America. The studies reported here investigated the influences of spotted knapweed patch size and stem density on U. quadrifasciata larval populations overwintering within capitula in the Upper Peninsula of Michigan, USA. An inverse relationship was found between the percentage of capitula with U. quadrifasciata larvae and spotted knapweed patch size in 2002 from Houghton county, MI. In 2003, an inverse relationship was also found in the south region of the study area in Houghton and Keweenaw counties, Michigan. The percentage of capitula with U. quadrifasciata larvae and spotted knapweed patch size were positively related for the central region. No relationship was found for the North region in 2003. Dispersal of U. quadrifasciata is directed north-east along the Keweenaw Peninsula, Michigan. With this directed spread, areas with well-established populations of U. quadrifasciata would provide source individuals for new colonization. Spotted knapweed patch size may play an important role in the overwintering populations of U. quadrifasciata as a result of dispersal.     

A new species of Urophora Robineau-Desvoidiy, 1830 (Diptera, Tephritidae) from Iran

Urophora merzisp. n. reared from flower heads of Centaurea behen Linnaeus is described from Iran. It is similar to Urophora campestris, Urophora sachalinensis, Urophora stylata, Urophora tsoii and Urophora vera in wing pattern with 3 well developed crossbands and indistinct subbasal crossband, differing in aculeus tip with two pairs of diminished preapical steps and different host plants.     

A revision of the western Palaearctic species of Urophora Robineau-Desvoidy (Diptera: Tephritidae)

Abstract A key is provided to twenty-four western Palaearctic species of Urophora Robineau-Desvoidy. The hosts of twenty-three species which attack Asteraceae are listed, including those being used or investigated as possible weed biocontrol agents. The species are divided into four species groups and the differing host relationships and types of galls induced by these groups are discussed. U.lopholomae sp.n. and U.affinis ssp. calcitrapae ssp.n., associated with Centaurea (Lopholoma) spp. and C. (Calcitrapa) spp. respectively, are described. U. algerica (Hering) and U.sjumorum (Rohdendorf) are both treated as subspecies of U. quadrifasciata (Meigen). U.pontica is given full specific status and U.hispanica is removed from synonymy. The following new synonymies are made (junior synonyms in parentheses): U. angustifascia (Hering) (= Euribia phaeocera Hering); U. cardui (Linnaeus) (= U. reaumurii Robineau-Desvoidy, lectotype designated); U. jaceana (Hering) (= E.conyzae Hering); U.maura (Frauenfeld) (= E. tecta Hering); U. mauritanica Macquart (= U. lejura Rondani, Trypeta macrura Loew); U.solstitialis (Linnaeus) (= E.sonderupi Hering, U. veruata Rondani ); U.stylata (Fabricius) (= E.pia Hering, U. vulcaanica Rondani); U. terebrans (Loew) (= E. approximata Hering, T. eriolepidis Loew, E. manni Hendel). The possibility that U. quadrifasciata is a species complex is discussed; it is also suggested that U.affinis and U.jaceana represent the morphological extremes of a complex. The misuse of the name Musca stylata Fabricius in the genus Myopites Blot is noted.     

Growth and development of larvae and galls of Urophora cardui (Diptera,Tephritidae) on Cirsium arvense (Compositae)

Summary The tephritid fly Urophora cardui induces a large multi-chambered gall within the stems of Cirsium arvense. Three distinct phases of gall development have been identified as initiation, growth, and maturation. During initiation the insect gains control of tissue development and during the gall's growth phase parenchyma cells proliferate rapidly surrounding the larvae with thick layers of cells. Patches of primary nutritive cells appear along the surface of larval chambers during the growth phase but few of these cells are consumed. In the gall's maturation phase, thick layers of secondary nutritive cells appear around the surface of larval chambers and the remaining gall parenchyma lignifies. Secondary nutritive cells are the primary food of U. cardui.The gall expands rapidly during the growth phase then abruptly slows at the beginning of the maturation phase. Rate of gall growth is dependent upon the number of larvae per gall but the number of larvae does not affect duration of this phase.Larvae remain in the second instar throughout the growth phase and grow slowly. Once the gall enters the maturation phase and the secondary nutritive cells appear, the larvae moult to the third instar and grow quickly. Larvace attain over 98% of their final weight during the maturation phase and consume all secondary nutritive cells.It is postulated that larvae do not feed extensively on primary nutritive cells since these cells play a key role in gall morphogenesis. The appearance of secondary nutritive cells stimulates larval feeding at a time when gall growth and development is finished.     

Biology and host specificity of the chromolaena stem gall fly, Cecidochares connexa (Macquart) (Diptera: Tephritidae)

Abstract The stem-galling tephritid fly Cecidochares connexa (Macquart) was investigated as a potential biocontrol agent against the weed Chromolaena odorata (L) King & Robinson in Indonesia. Adults were tested in choice and no-choice tests, on 55 non-target plant species in 17 families. No oviposition was recorded on 53 of the species, while oviposition but no larval development was recorded on two. Field releases commenced in 1995 and establishment was immediate. The gall fly is now widely established in most Indonesian provinces, where gall parasitism and predation is generally low.     

Quantifying pepper maggot (Diptera: Tephritidae) oviposition and infestation over time

In 1998 and 1999, pepper maggot flies, Zonosemata electa (Say), were excluded from pepper plants with row covers for 0-6 wk after initial oviposition was detected. The proportion of oviposition attempts (scars) and larval infestation that occurred each week and the cumulative oviposition and infestation over time were determined. Due to environmental factors, initial oviposition was delayed, and the numbers of oviposition scars on fruit and flies caught on traps were lower in 1998 than in 1999. The proportions of scarred or infested fruit were low (< 8% of total) during the first 7 d after the pest was detected each year. Oviposition peaked 8-14 d after beginning in 1998, but not until 21-28 d after the initial scar was detected in 1999. Because systemic insecticides tend to provide control of adults and most hatching larvae, it may be possible to delay the initial insecticide application for up to a week after oviposition commences and still minimize fruit damage. There was no association with either year between the proportion of flies captured on traps and the proportion of oviposition scars on fruit the same week or 1 and 2 wk later.     

Energy and water conservation in frozen vs. supercooled larvae of the goldenrod gall fly, Eurosta solidaginis (fitch) (Diptera: Tephritidae)

Insects that tolerate severe cold during winter may either supercool or tolerate ice forming within the tissues of the body. To compare the relative advantages of freezing and supercooling, we measured rates of CO(2) production and water loss in frozen and supercooled goldenrod gall fly larvae (Eurosta solidaginis). As an important first step, we measured the time required for ice content and metabolic rate to stabilize upon freezing. Ice content stabilized after only three hours of freezing at -5 degrees C, whereas CO(2) production required 12 hours to stabilize. Subsequent experiments found that freezing greatly reduced both water loss and metabolic rate. Comparisons of supercooled and frozen larvae at -5 degrees C indicated that CO(2) production fell 47% with freezing and water loss decreased 35%. As temperature decreased to -10 and -15 degrees C, CO(2) production fell exponentially and was no longer detectable at -20 degrees C with our measurement system. Our results demonstrate that freezing significantly reduces energy consumption during the winter and may therefore improve winter survival and spring fecundity. The advantages of freezing over supercooling would drive selection toward insect freeze tolerance and also toward higher supercooling points to increase the duration of freezing each winter.     

Cuticular lipids and desiccation resistance in overwintering larvae of the goldenrod gall fly, Eurosta solidaginis (Diptera: Tephritidae)

Within their gall, larvae of the goldenrod gall fly (Eurosta solidaginis) experience severe desiccating conditions as well as highly variable thermal conditions and extreme cold during winter. Through the autumn and early winter, field-collected larvae acquired markedly enhanced resistance to desiccation and freezing. At the same time, they increased their cuticular surface hydrocarbons. Hydrocarbons were the major lipid class extracted by hexane or chloroform from the cuticular surface of overwintering gall fly larvae. The major hydrocarbon classes were the 2-methylalkanes which consisted mainly of 2-methyltriacontane. 2-Methyltriacontane comprised 48-68% of the total hydrocarbons during the larval stages. Total hydrocarbons increased from 122 ng/larva in early third instar larvae collected in September to 4900 ng/larva in those collected in January. Although washing of the cuticular surface with chloroform or chloroform:methanol (2:1, v:v) caused marked increases in rates of water loss, treatment with hexane and methanol had little effect on water loss rates.     

The problem of optimal clutch size in a tritrophic system: the oviposition strategy of the thistle gallfly Urophora cardui (Diptera,Tephritidae)

The problem of optimal clutch sizes is a central theme in life history theory. Optimal allocation of eggs is especially complicated for insects in tritrophic systems. In this study we analyze some of the processes determining clutch sizes of the thistle gallfly Urophora cardui, a monophagous tephritid fly associated with Cirsium arvense. U. cardui forms multilocular shoot galls, which vary broadly in their size and number of their gall cells. We investigate various fitness consequences of gall size. An analysis of the number of cells per gall (which is correlated with gall diameter and gall weight) showed that in U. cardui there is mutual facilitation rather than larval competition. Increasing numbers of larvae per gall led to a decreasing mortality and increasing larval weight. Larval weight in turn was positively correlated with the probability of survival to adulthood and with adult weight and fecundity. Thus, all fitness parameters measured favoured large galls. Clutch sizes in oviposition experiments were distinctly larger than the number of gall cells of field populations and in cage experiments, suggesting high mortality of eggs and/or early larval instars. There was a significant relationship between the internal structure (i.e., the size of the growing point) of the bud and clutch size, suggesting that U. cardui females are able to measure bud quality and adapt clutch sizes accordingly. Clutch size was positively correlated with the female's age at first oviposition and negatively with the number of previous ovipositions and previously laid eggs. Since the potential egg capacity per female is higher than the average number of larvae it is likely to produce during its short adult lifespan, U. cardui females tend to be time-limited rather than egglimited, which might favour large clutches once an appropriate oviposition site has been located. As the development of the gall and hence the fate of a clutch depends on a number of unpredictable factors, exclusive concentration of eggs in a few large clusters would involve risks which could be avoided by increasing the number of clutches. Therefore we interpret the high variation of clutch sizes in U. cardui as a mixed strategy of bet hedging and gambling.     

Olive fruit fly (Diptera: Tephritidae) populations in relation to region, trap type, season, and availability of fruit

Olive fruit fly, Bactrocera oleae (Gmelin), was monitored with adult captures by season and trap type, and was related to fruit volume and nonharvested fruit to elucidate the occurrence of the newly introduced pest in California. The highest numbers of adults captured in ChamP traps in olive trees, Olea europaea, were in October in an inland valley location, and in September in a coastal location. Comparisons of trap types showed that the number of olive fruit fly adults captured in Pherocon AM traps in a commercial orchard was significantly greater than in ChamP traps. A significantly greater number of females were captured in Pherocon AM traps with bait packets and pheromone lures than traps with pheromone lures alone, while a significantly greater number of adults and males were captured in traps with pheromone lures alone. Significantly more adults were captured in ChamP traps with bait packets and pheromone lures versus traps with bait packets alone. Fruit volume increased by four times from mid-June to mid-November. Olive fruit fly was found to oviposit on small olive fruit <1 cm3 shortly after fruit set, the maximum number of ovipositional sites per fruit occurred in October, and the greatest number of pupae and adults were reared from fruit collected in September and October. The highest numbers of pupae were collected from nonharvested fruit in March when high numbers of adults were captured in the same orchard.     

Mitochondrial DNA variation among host races of Eurosta solidaginis Fitch (Diptera: Tephritidae)

Eurosta solidaginis Fitch (Diptera: Tephritidae) induces galls on two species of goldenrod, Solidago (Compositae), in the northern regions of the United States. Recent studies have demonstrated that E. solidaginis is comprised of two host races that differ in adult emergence times, mate preference, and host preference. However, it is not known how much genetic variation, if any, exists among E. solidaginis host-associated populations west of Minnesota where the two host races occur in sympatry. Sequencing analysis was used to characterize two mitochondrial gene fragments: (1) NADH1 dehydrogenase (ND1: 539 bp) and (2) cytochrome oxidase II + tRNA(Lys) + tRNA(Asp) (CO2KD: 396 bp) from sympatric, host-associated populations of E. solidaginis in North Dakota. Our results indicated that two genetically distinct lineages exist among E. solidaginis in North Dakota that correspond with host-plant association.     

Relevant genetic differentiation among Brazilian populations of Anastrepha fraterculus (Diptera,Tephritidae)

We used a population genetic approach to detect the presence of genetic diversity among six populations of Anastrepha fraterculus across Brazil. To this aim, we used Simple Sequence Repeat (SSR) markers, which may capture the presence of differentiative processes across the genome in distinct populations. Spatial analyses of molecular variance were used to identify groups of populations that are both genetically and geographically homogeneous while also being maximally differentiated from each other. The spatial analysis of genetic diversity indicates that the levels of diversity among the six populations vary significantly on an eco-geographical basis. Particularly, altitude seems to represent a differentiating adaptation, as the main genetic differentiation is detected between the two populations present at higher altitudes and the other four populations at sea level. The data, together with the outcomes from different cluster analyses, identify a genetic diversity pattern that overlaps with the distribution of the known morphotypes in the Brazilian area.     

Acquisition of freezing tolerance in early autumn and seasonal changes in gall water content influence inoculative freezing of gall fly larvae,Eurosta solidaginis (Diptera,Tephritidae)

We examined seasonal changes in freeze tolerance and the susceptibility of larvae of the gall fly, Eurosta solidaginis to inoculative freezing within the goldenrod gall (Solidago sp.). In late September, when the water content of the galls was high (approximately 55%), more than half of the larvae froze within their galls when held at -2.5 degrees C for 24 h, and nearly all larvae froze at -4 or -6 degrees C. At this time, most larvae survived freezing at > or = -4 degrees C. By October plants had senesced, and their water content had decreased to 33%. Correspondingly, the number of larvae that froze by inoculation at -4 and -6 degrees C also decreased, however the proportion of larvae that survived freezing increased markedly. Gall water content reached its lowest value (10%) in November, when few larvae froze during exposure to subzero temperatures > or = -6 degrees C. In winter, rain and melting snow transiently increased gall water content to values as high as 64% causing many larvae to freeze when exposed to temperatures as high as -4 degrees C. However, in the absence of precipitation, gall tissues dried and, as before, larvae were not likely to freeze by inoculation. Consequently, in nature larvae freeze earlier in the autumn and/or at higher temperatures than would be predicted based on the temperature of crystallization (T(c)) of isolated larvae. However, even in early September when environmental temperatures are relatively high, larvae exhibited limited levels of freezing tolerance sufficient to protect them if they did freeze.     

Genetical and biochemical comparisons of alcohol dehydrogenase isozymes from Anastrepha fraterculus and A. obliqua (Diptera: Tephritidae): Evidence for gene duplication

The electrophoretic patterns of the enzyme alcohol dehydrogenase (ADH) from Anastrepha fraterculus and A. obliqua were studied. Two loci were found to code for the enzyme in A. fraterculus, and three in A. obliqua. In both species, all isozymes were active in third-instar larvae. A cationic isozyme (Adh-1) was active mainly in the visceral fat body of both species. In A. fraterculus, the locus had an anionic polymorphic isozyme (Adh-3) that was detected in the parietal fat body. In addition to these two loci, a third locus for an anionic isozyme (Adh-2), which was active in the digestive tube of larvae, was present in A. obliqua and probably resulted from gene duplication. For both species, multiple forms of the isozymes are formed by binding of an NAD-carbonyl compound, as in Drosophila melanogaster. Both larvae and early pupae of A. obliqua had almost twice the specific ADH activity as A. fraterculus. The ethanol content of the host fruit infested with A. obliqua (red mombim) was also higher than that of the host fruit infested with A. fraterculus (guava).This research was supported by grants from Conselho Nacional de Desenvolvimento Científico e Tecnologico (CNPq-PIG 40.2486/82).     

Native and introduced host plants of Anastrepha fraterculus and Ceratitis capitata (Diptera: Tephritidae) in northwestern Argentina

Wild or commercially grown, native and exotic fruit were collected in 30 localities in the Tucumán province (NW Argentina) from January 1990 to December 1995 to determine their status as hosts of Anastrepha fraterculus (Wiedemann) and/or Ceratitis capitata (Wiedemann), the only two fruit fly species of economic and quarantine importance in Argentina. A total of 84,094 fruit (3,466.1 kg) representing 33 species (7 native and 26 exotic) in 15 plant families were sampled. We determined the following 17 host plant associations: Annona cherimola Miller (Annonaceae), Citrus paradisi Macfadyn (Rutaceae), Diospyros kaki L. (Ebenaceae), Eugenia uniflora L., Psidium guajava L., Myrcianthes pungens (Berg) Legrand (Myrtaceae), Ficus carica L. (Moraceae), Juglans australis Grisebach (Juglandaceae), Mangifera indica L. (Anacardiaceae), Eriobotrya japonica (Thunb.) Lindl., Prunus armeniaca L., P. domestica L., and P. persica (L.) Batsch (Rosaceae) were infested by both A. fraterculus and C. capitata. Citrus aurantium L., Citrus reticulata Blanco, Citrus sinensis (L.) Osbeck (Rutaceae), and Passiflora caerulea L. (Passifloraceae) were only infested by Ceratitis capitata. Out of a total of 99,627 adults that emerged from pupae, 69,180 (approximately 69.5%) were Anastrepha fraterculus, 30,138 (approximately 30.2%) were C. capitata, and 309 (approximately 0.3%) were an unidentified Anastrepha species. Anastrepha fraterculus predominated in native plant species while C. capitata did so in introduced species. Infestation rates (number of larvae/kg of fruit) varied sharply from year to year and between host plant species (overall there was a significant negative correlation between fruit size and infestation level). We provide information on fruiting phenology of all the reported hosts and discuss our findings in light of their practical (e.g., management of A. fraterculus and C. capitata in citrus groves) implications.     

Host-marking pheromone and use of previously established oviposition sites by the mediterranean fruit fly (Diptera: Tephritidae)

Under controlled conditions, the Mediterranean fruit fly, Ceratitis capitata(Wiedemann) preferred to initiate oviposition into preexisting, naturally formed oviposition punctures in a host fruit, kumquat (Fortunella japonica),over establishing new sites on the fruit. This preference was expressed despite the presence of naturally deposited host-marking pheromone (HMP)shown previously to deter oviposition. An almost-identical preference for existing punctures was expressed when females were presented with fruit bearing artificially made punctures on which HMP had been naturally deposited. Using artificial punctures and HMP extracts, the occurrence of punctures was manipulated independently of the presence of HMP.Under field-cage conditions, we found that (1) punctures stimulated egg-laying on kumquats, regardless of HMP treatment; (2) HMP extract inhibited egg-laying, regardless of the occurrence of punctures; and (3) the extent to which HMP inhibited egg-laying was greater on fruit free of punctures than on fruit bearing them. The physiological, evolutionary, and pest management implications of these results are discussed.     

Genetic differences among natural and laboratory-reared populations of the olive-fruit fly Dacus oleae (Diptera: Tephritidae)

Twelve wild populations of the olive-fruit fly Dacus oleae from around the Mediterranean basin and two laboratory populations were examined for their electrophoretic profiles at two esterase loci. The genetic distances among wild and laboratory populations were consistently greater than the distances among wild populations. There was a pattern in this genetic differentiation, in that the most common allele decreased in frequency during culture in the laboratory, thus causing an increase of heterozygosity in laboratory populations. The findings are discussed in the light of assessing the genetic quality of mass-laboratory (or factory) cultures of economically important insects.

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Zusammenfassung Die elektrophoretischen Profile zweier Esterase-Loci von zwölf natürlichen Populationen der Olivenfliege Dacus oleae aus Ländern des Mittelmeerbeckens und von zwei Laboratorium-Populationen wurden untersucht. Die genetischen Abstände zwischen natürlichen und Laboratorium-Populationen waren konsistent grösser als die Abstände zwischen natürlichen Populationen. Bei dieser genetischen Differenzierung zeigte sich eine Regelmässigkeit. Die häufigsten Allele nahmen während der Zucht im Laboratorium in ihrer Häufigkeit ab, was zu einer Zunahme der Heterozygosis in Laboratorium-Populationen führte.Diese Resultate werden diskutiert im Zusammenhang mit der genetischen Qualität von Massenzuchten wirtschaftlich wichtiger Insekten im Laboratorium und in der Industrie.

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On leave of absence from Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J1.

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This is paper No. VII of the series The Genetics of Dacus oleae     

Effect of emergence time on the reproductive parameters of mass-reared Anastrepha ludens (Diptera: Tephritidae) flies

In the mass rearing of fruit flies, the adult emergence time is gradual, due to factors such as variation in food consumption in the larval phase, the female oviposition behavior and environmental conditions, among others. Here, we investigate the effect of emergence time on sex ratio, fecundity, fertility, body size and mating performance in mass-reared Anastrepha ludens (Diptera: Tephritidae) flies. The results of the study indicated that the emergence of the flies is gradual and lasts approximately 96?h, but the highest proportion of emerged flies was observed at 48?h. The flies emerging at 24 and 48?h showed higher fecundity than those emerging at 72 and 96?h, but there were no significant differences in the sex ratio, fertility and male mating performance. Body size was significant, the flies that emerged at 24, 48 and 72?h were bigger than those emerged at 96?h. The discussion focuses on the effect of emergence time on the rearing processes and release of the Mexican fruit fly.