Starvation and the Mating Success of Wild Male Mediterranean Fruit Flies (Diptera: Tephritidae)

Recent evidence suggests that the nutritional state of male Mediterranean fruit flies, Ceratitis capitata (Wied.) (medfly), is an important influence on various components of their reproductive biology, including mating success. The objective of the present study was to examine experimentally the effect of temporary starvation on the mating success of wild male C. capitata. Males were maintained on protein–sugar or sugar-only diets, and for each diet we compared the mating success of continuously fed males versus males starved for 18 or 24 h immediately before testing. In trials conducted on field-caged, host trees, males starved for 24 h obtained only about half as many matings as fed males for both diets. However, when the starvation period was 18 h, starved males reared on the protein–sugar diet mated significantly less frequently than fed males, whereas starved males reared on sugar mated as often as fed males. Measurements of male pheromone calling and female attraction revealed that reduced mating success likely reflected the decreased signaling activity of starved males.     

Male position and calling effort together influence male attractiveness in leks of the medfly,Ceratitis capitata (Diptera: Tephritidae)

Despite the close association between lek mating systems and the study of female mate choice, male mating success in leks is often associated with other aspects of sexual selection as well as female choice of male display traits. Males of the medfly Ceratitis capitata form leks on the undersides of leaves of their host plants. By experimentally creating artificial leks, we show that male success at attracting females depends not only on male calling effort (pheromone production dispersed by wing movement), but also on the position of the male within a lek. Males in the highest position in the artificial lek (closest to the light) attracted more females, and received more visits from those females. In our experiment, we deliberately minimized the visual cues that females approaching a male could use and, under these conditions, found no associations between male attractiveness and male size, weight or fluctuating asymmetry, either of the wings or sex setae (a pair of bilateral supra‐fronto‐orbital bristles). The latter result contrasts with earlier studies showing a significant negative association between sex setae fluctuating asymmetry and mating success. Accordingly, we conclude that symmetry of the male sex setae has no role in nonvisual communication (e.g. through directing pheromone plumes). Mating patterns associated with this insect are therefore every bit as complex as those in vertebrate leks. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 479–487.     

Sexual competitiveness of sterile Ceratitis capitata males exposed to essential oils from non-host plant species native to Argentina

The sterile insect technique (SIT) is used to control fruit fly pests, such as the Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). Enhancing sexual competitiveness of mass-reared sterile males can contribute to making this technique more effective. It has been shown that exposure to volatiles from essential oils (EOs), such as ginger root oil (GRO) and those from host fruits, increases male mating success. We evaluated the effect of EOs from non-host species native to Argentina, Schinus polygama (Cav.) Cabrera (Anacardiaceae) and Baccharis spartioides (Hook. & Arn.) Remy (Asteraceae), on the sexual competitiveness of sterile C. capitata males. In field cage experiments, sterile males exposed to S. polygama EO increased their mating success. In addition, sterile males exposed to this EO achieved more matings on trees than non-exposed males, thus suggesting the former are more prone to locate and defend the pheromone-calling territory. Deprivation of water and/or food significantly reduced males' life span, but exposure to S. polygama EO and GRO did not affect their survival. Schinus polygama EO is composed of mono- and sesquiterpenes with behavioral and electroantennographic responses in medflies, indicating that semiochemicals that boost medfly sexual competitiveness combine in this EO.     

Attraction of female Chiracanthium mildei(Araneae: Clubionidae) to olfactory cues from maleMediterranean fruit flies Ceratitis capitata(Diptera: Tephritidae)

Chiracanthium mildei, a common sac spider (Clubionidae) in Israel, is an important predator of pest insects in citrus and apple orchards. Field observations indicate that the females of this hunting spider are attracted to traps containing the parapheromone trimedlure and males of the Mediterranean fruit fly (Ceratitis capitata),which were caught in these traps. Laboratory testsshow that C. mildei females are attractedto olfactory cues from male C. capitata, but notto trimedlure. This suggests that C. mildeimay be an important nocturnal predator of C.capitata.     

Settlement Patterns of Mediterranean Fruit Flies in the Tree Canopy: An Experimental Analysis

Males of the Mediterranean fruit fly, Ceratitis capitata (medfly), defend individual leaves of host and non-host trees as mating territories and attract females via production of a sex pheromone (a behavior termed ‘calling’). Males tend to aggregate within the tree canopy, and the present study examined the influence of (1) location and (2) resources on female visitation to male aggregations. Males were placed in screen-covered containers, which were suspended on field-caged trees at two locations selected to differ in only one of the following parameters: height above ground (low versus high), leaf density (sparse versus dense), distance to main trunk (canopy edge versus center), proximity to a food source (bird feces absent or present), and proximity to a host fruit (oranges absent or present). Females were released, and we periodically recorded the number of calling males in each of the test aggregations as well as the number of females sighted within 15 cm of each male aggregation. Male calling did not differ between treatments in any of the experiments. However, females were more frequently sighted near males calling (1) in dense foliage, (2) near the central trunk, (3) near bird feces, and (4) near oranges. In an additional experiment, we compared male settlement (in the absence of females) on leaves in the same sites used previously to determine the degree of congruence between the sexes in microhabitat use. Aside from the lack of center-edge effect, males displayed the same settlement patterns as females. In a final experiment, we found no effect of male calling on the distribution of other males: released males were sighted with equal frequency near cups containing mature, calling males and cups containing immature, non-calling males. Medfly lek behavior is discussed in light of these findings.     

Sterile males of Ceratitis capitata (Diptera: Tephritidae) as disseminators of Beauveria bassiana conidia for IPM strategies

Sterile Mediterranean fruit fly, Ceratitis capitata (Wied.), males were evaluated as vectors to spread Beauveria bassiana (Bals) conidia to wild C. capitata populations under field conditions. The inoculated sterile males were released by air, using the chilled adult technique over 7000 ha of coffee growing in Chimaltenango, Guatemala, Central America. The impact of releases was determined using dry traps baited with a food attractant. The effects of these releases on Apis mellifera, Linnaeus (honey bee), Hypothenemus hampei, Ferrari (coffee berry borer) and the parasitic mite Varroa destructor (Oudeman) were also evaluated. Inoculated sterile males were able to transmit fungal spores to 44% of the wild C. capitata flies captured in traps, which likely were infected through intra- and intersexual interactions during leks, mating or mating attempts. There was no transmission of the fungal spores to non-target insect species such as coffee berry borer, honey bees or varroa. We conclude that sterile males of Mediterranean fruit fly inoculated with B. bassiana can act as effective vectors of conidia to wild populations, constituting a safe, environmentally friendly and selective alternative for suppressing the medfly under a Sterile Insect Technique-based IPM approach.     

Contrasting foraging related behaviours in two sympatric wasps (Vespula maculifrons and V. germanica)

ABSTRACT.

• 1 Using pinned freshly killed wasps (yellowjackets) to simulate feeding animals, it was found that V. germanica was socially facilitated, and concentrated its foraging activity on those feeders with the most pinned wasps (twenty). V. maculifrons foragers responded inversely, preferentially foraging at feeders with few or no pinned wasps.
• 2 Using hand-painted drawing pins (thumb tacks) as wasp models, similar results were found, indicating that visual, rather than olfactory, cues were responsible for the observed distribution.
• 3 Vespula maculifrons and V. germanica exhibit aggression while foraging at honey-baited feeders. Both species attack conspecifics at frequencies lower than would be expected under random encounter.

     

Diet and size influence sexual advertisement and copulatory success of males in Mediterranean fruit fly leks

1. The objective of the work reported here was to test the hypothesis that in insects that invest considerable energy in sexual displays and courtship, foraging successfully for food affects their subsequent performance and copulatory success in leks. Accordingly, the interactions between body size and diet on initiation of lekking behaviour and copulatory success in male Mediterranean fruit flies Ceratitis capitata (Diptera: Tephritidae) were investigated. 2. Protein‐fed males were heavier and contained more protein and less lipid reserves than protein‐deprived males. Protein‐fed males were more likely to emit pheromone in leks and, consequently, were more likely to copulate than protein‐deprived males. Furthermore, protein‐fed males tended to start calling earlier than their nutritionally deprived competitors. 3. Though size was not related to initiation of lek behaviour, large males were more likely to copulate than small males. Among protein‐fed males, large individuals tended to mate earlier than smaller individuals. 4. Generally, in lek mating systems where a considerable investment of time and energy is required by males, foraging successfully for nutritional resources prior to engaging in territorial or courtship behaviour is essential for reproductive success.     

Comparative response to citrus foliage and citrus fruit odour by wild and mass-reared sterile Mediterranean fruit fly males of a genetic sexing strain

In greenhouse behavioural assessments conducted at Seibersdorf, Austria that allowed flies the choice of different types of potted host trees and plants, it was found that mature laboratory mass-reared Mediterranean fruit fly males, Ceratitis capitata (Wied), (Dipt. Tephritidae), strain Vienna-42 (temperature-sensitive lethal genetic sexing strain) showed the same preference for orange foliage, over other plants types and parts, as wild males. They aggregated in leks, released pheromone, and courted approaching females almost exclusively on orange foliage. Even though a number of other trees and plants were available to Vienna-42 males, less than 1% of these sexual activities occurred on the foliage or other plant parts of non-Citrus trees and not a single mating occurred there. In choice tests carried out in Chios, Greece in large field cages housing naturally planted orange trees, it was determined that mature and sterile Mediterranean fruit fly males of the same sexing strain responded to the odour emanating from the flavedo (due to superficial cuts made in the fruit peel containing the oil glands) of ripening sweet, sour oranges and lemons, in a similar intensity, order of fruit preference and time of day as did mature males of the local wild population. Males of both strains were frequently observed contacting with their mouth parts the oils exuding from the cuts made in the flavedo of the orange peel, or exhibiting homosexual activity on, or near the cuts. The results show that mass-reared, sterile males of the Vienna-42, genetic sexing strain behave in a comparable way to wild males in an important component of habitat location (odour of host foliage and host fruit) and hence are competitive with them in these respects. None of the standard international quality control tests for sterile Mediterranean fruit flies evaluates this important habitat location behaviour, which is a prerequisite for the successful encounter of the sexes in a sterile release programme.     

Foraging and spatial dispersion in protein-scavenging workers ofVespula germanica andV. maculifrons (Hymenoptera: Vespidae)

A series of experiments on the discovery of meat bait by scavenging workers ofV. germanica andV. maculifrons showed that workers oriented to meats by visual cues and olfactory cues. Scavening workers ofV. germanica andV. maculifrons responded positively to the sight of conspecifics at meat baits; i.e., meat with (confined) wasps received more visits than meat without wasps. This attraction to conspecific workers on meat baits provides evidence of local enhancement, in that the presence of conspecifics at meat bait directs other wasps to a particular spatial locality. Local enhancement by yellowjackets foraging for meat may contribute to the clumped distribution of worker populations noted in studies of workers captured in meat-baited traps. We hypothesize that local enhancement of foraging is a ubiquitous behavior in species of theV. vulgaris species group and may be one attribute explaining their ecological success.     

Sex differences in movement between natural feeding and mating sites and tradeoffs between food consumption,mating success and predator evasion in Mediterranean fruit flies (Diptera: Tephritidae)

Summary Systematic quantitative observations of the location and diel pattern of adult Mediterranean fruit fly, Ceratitis capitata (Wiedemann), activities were carried out in an orange grove and surroundings on the island of Chios in Greece. Natural fly foods were assessed for their contribution to fly longevity, fecundity and fertility. There were diel shifts in male and female location. Females required a substantial and varied diet to realize peak fecundity. This diet was acquired away from the primary host, orange. Foraging for food throughout most of the day on fig and non-host foliage (including feeding on bird droppings) as well as on fig fruit and grapes, females dispersed and fed more than males. A diet of grapes alone did not support any fecundity, contributing only to longevity. A diet of figs alone, on the other hand, sustained both longevity and egg production. Bird feces alone supported neither egg production nor longevity. However, when added to a diet of figs, bird feces significantly increased fly fecundity. Throughout most of the day, males aggregated in leks within the inner canopy of the primary host, orange. The arrival here during the warmest hours of the day of receptive females, followed by pair formation, reinforced the lek mating system on host foliage. In the afternoon, females shifted to orange fruit where they suffered from high predation mortality while ovipositing. Soon after, males also shifted to orange fruit, where they attempted matings with non-receptive ovipositing females. Male feeding on fig fruit occurred late in the day, a time when they were least likely to find a mate. Male survival did not differ between the natural diets. Tradeoffs between food consumption, mating success and predator evasion are discussed for each sex and related to fruit fly mating systems.     

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.     

Acceptability and suitability of six fruit fly species (Diptera: Tephritidae) for Kenyan strains of Psyttalia concolor (Hymenoptera: Braconidae)

Host acceptability and suitability Psyttalia concolor (Szépligeti) is a koinobiont, larval parasitoid of tephritid fruit flies. Individuals of P. concolor were field-collected from coffee in the central highlands of Kenya, and cultured initially on Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann). They were then examined for their ability to oviposit in and develop on five other tephritid species that are pests in Kenya. In addition to the medfly, acceptability for oviposition and suitability for development were tested against the mango fruit fly, Ceratitis cosyra (Walker), the Natal fruit fly, Ceratitis rosa Karsch, Ceratitis fasciventris (Bezzi), Ceratitis anonae Graham and the melon fruit fly, Bactrocera cucurbitae (Coquillett). Ceratitis capitata and C. cosyra were accepted as hosts significantly more often than the other species. Superparasitism was recorded only from C. capitata and C. cosyra. Two days after oviposition, parasitoid eggs in C. fasciventris and B. cucurbitae were encapsulated, whereas those in C. rosa and C. anonae were encapsulated, and often melanized. Ceratitis capitata was the most suitable host for Kenyan populations of Psyttalia concolor in terms of progeny production, and proportion of female progeny.     

Intra-tree foraging behavior of Ceratitis capitata flies in relation to host fruit density and quality

We examined the intra-tree foraging behavior of individually-released, wild-population Mediterranean fruit flies (medflies), Ceratitis capitata (Wiedemann), on field-caged host trees bearing each of three different densities (0, 3, or 12 per tree) of non-infested host fruit (kumquat) or each of two levels of fruit quality (12 non-infested fruit or 12 fruit infested with eggs and covered with host marking pheromone). With increasing density of non-infested fruit, medflies tended to remain longer in trees, visit more fruit before leaving, oviposit more often, accept a proportionately smaller number of fruit visited, and emigrate sooner after the last egg was laid (i.e. have a shorter Giving-Up-Time). Medflies spent much less time, oviposited much less often, and exhibited a longer Giving-Up-Time on trees harboring pheromone-marked fruit than non-infested fruit. Variation in temperature within the range at which experiments were conducted (25–36°C) had little detectable influence on foraging behavior. We compare our findings with published findings on the intra-tree foraging behavior of another tephritid fly, Rhagoletis pomonella (Walsh), and with current foraging behavior theory. We discuss implications of our findings with respect to medfly management strategies, particularly fruit stripping in eradication programs and use of synthetic marking pheromone for control.

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Résumé Nous avons étudié le comportement de prospection dans un arbre, de femelles d'une population sauvage de C. capitata, libérées individuellement à l'intérieur de cages contenant des Eriobotrya japonica (kumquat), portant chacun 3 densités différentes de fruits no contaminés (0, 3, 12 par arbre) et chacun 2 niveaux de qualité de fruits: 12 fruits non infestés ou 12 fruits contaminés par des oeufs et recouverts de phéromone de marquage de l'hôte. C. capitata avait terndance à rester plus longtemps dans les arbres, à visiter plus de fruits avant le quitter, à pondre plus souvent, à accepter proportionnellement un nombre plus réduit de fruits déjà visités, à émigrer plus tôt après la ponte du dernier oeuf (c'est-à-dire à présenter un temps d'abandon plus bref), quand la densité des fruits non contaminés augmentait. C. capitata a dépensé beaucoup moins de temps, pondu beaucoup moins souvent, et présenté un temps d'abandon plus long sur les arbres portant des fruits marqués par la phéromone que sur ceux ayant des fruits non contaminés. Les variations de température dans la gamme de cells où les observations ont eu lieu (23–36°C) n'ont eu qu'une faible influence décelable sur le comportement de prospection. Nous avons comparé nos résultats avec ceux publiés sur la prospection à l'intérieur de l'arbre par une autre téphritide (Rhagoletis pomonella) et avec la théorie dominante sur le comportement de prospection. Nous discutons les conséquences de nos résultats sur les stratégies de lutte contre C. capitata, en particulier l'élimination des fruits dans les plans d'erradication et l'utilisation de phéromone synthétique de marquage.

     

Lekking and the small-scale distribution of the sexes in the Caribbean fruit fly,Anastrepha suspensa (Loew)

Male and female Anastrepha suspensa(Loew) had a clumped distribution in the foliage of their guava host plants. Males were no closer to other males than they were to females or than females were to other females. Flies were often found in roughly the same locations over time. However, contemporaries (flies present at the same time) were closer to each other than subsequent flies were to their predecessors. Males were more likely to be found near spots previously occupied by males than they were to spots used previously by females. Some trees had more flies than others, but there was no regional (northwest, etc.) preference within trees. Females were no more likely to be found in the vicinity of clumped (lekking) males than they were by isolated males. About a third of the females taken from inside leks had sperm in their spermathecae, and it is not clear if their motive for being in these areas was sexual. In pairs of males (within 15 cm of each other), the larger fly tends to be in a position farther up the branch, suggesting that larger males may control preferred territories. It seems possible that males attempting to intercept females accumulate in favorable microhabitats where females are likely to be concentrated and that leks have evolved from such clumping.     

Host plant influence on the mating success of male Mediterranean fruit flies: variable effects within and between individual plants

Observations of field-caged guava trees, Psidium guajava, revealed that males of the Mediterranean fruit fly (medfly), Ceratitis capitata, occasionally formed tight aggregations on the trunk and branches of certain trees. Males at these aggregation sites (stations) appeared to feed on the bark, and chemical analyses showed that stations contained high levels of the male attractant α-copaene whereas ‘nonstations’ on the same tree lacked this chemical. Previous work showed that male medflies exposed to pure α-copaene had a mating advantage over unexposed males. Here, we present data showing that the occurrence of stations is highly variable both within and between individual guava trees. Concurrent mating trials showed that male medflies exposed to entire guava trees containing stations or to individual stations for 3 h gained a mating advantage over unexposed males in tests conducted 1 or 3 days following exposure. In contrast, males exposed to entire trees lacking stations or only to nonstations on trees with stations had similar mating success as unexposed males. Additional experiments showed that exposure to guava leaves had no effect on male mating frequency but that exposure to fruits enhanced male mating success. The discussion considers potential mechanisms underlying the plant-induced increase in mating success and potential effects of α-copaene and other plant-borne compounds on the spacing of medfly leks in the environment.     

Riding the Trojan horse: combating pest insects with their own symbionts

Insects form an extremely large group of animals and bear a consequently large variety of associated microbes. This microbiota includes very specific and obligate symbionts that provide essential functions to the host, and facultative partners that are not necessarily required for survival. The Tephritidae is a large family that includes many fruit pests such as the Mediterranean fruit fly (the medfly, Ceratitis capitata) and the Olive fly (Bactrocera oleae). Community and functional analyses showed that the microbiota of both flies contribute to their diet, and affect host fitness parameters. The analysis of the microbiota's community structure of mass‐reared, sterilized medfly males used in the sterile insect technique revealed a strong reduction in Klebsiella spp. compared with non‐sterile and wild flies. Inoculation of sterile males with this gut population affected female mating behaviour as they preferentially mated with inoculated versus non‐inoculated males. These studies suggest that control can be significantly improved by manipulating symbionts in pest animals.     

Field efficacy of Ceratitis capitata (Diptera: Tephritidae) mass trapping technique on clementine groves in Spain

Mass trapping is being used in Mediterranean regions to control Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) in citrus. The technique is based on placing a high density of traps with an attractant (Ferag CC D TM^®, a three‐membrane dispensers of trimethylamine, ammonium acetate and diaminoalkane), and a toxicant, aiming to capture the highest numbers of adults in the grove. From 2006 to 2008, field trials were conducted in commercial Clementine (Citrus reticulata Blanco) groves to evaluate the efficacy against medfly of using different trap densities, 25, 50, 75 and 100 traps per ha. Based on the number of adults captured, fruit maturity parameters and medfly fruit damage, a 25 trap per ha density appears to be a valid stand‐alone method to protect mid‐season varieties (Clemenules) from the attack of C. capitata, because <0.5% of fruits on average were damaged at harvest. For early‐season varieties (Loretina and Marisol), mass trapping technique alone did not offer a satisfactory medfly control, because medfly populations were higher in the warmer months of the early‐season variety production, which led to a higher percentage of attacked fruits, even when increasing the trap density from 50 to 100 per ha. However, using 50 traps per ha density combined with chemical treatments only to the perimeter row of the grove gave good results, because <2% of fruits in average were damaged at harvest.     

Developmental time,longevity, reproductive capacity and sex ratio of the mealybug parasitoid Anagyrus sp. nr. pseudococci (Girault) (Hymenoptera: Encyrtidae)

Key biological parameters of Anagyrus sp. nr. pseudococci reared on the citrus mealybug Planococcus citri (Risso) were determined. The mean longevity of female wasps was 21.1 days, the median lethal time (LT₅₀) was 22 days, the mean number of offspring per female was 30.2 wasps and the sex ratio of the progeny was slightly male biased (1.1 males per female). Wasps fed with water showed a significantly lower longevity compared to that recorded for wasps fed with syrup for bee nutrition mixed with water. The longevity of female wasps was significantly higher compared to males when the syrup-water solution was provided as food. Longevity was significantly higher for female wasps fed with syrup and water in comparison with those exposed to host mealybugs. The mean development time of female and male wasps was 14.7±0.1 and 14.5±0.1 days, respectively.     

Are citrus species favorable hosts for the Mediterranean fruit fly? A demographic perspective

We studied, under laboratory conditions, demographic parameters of adult Mediterranean fruit flies, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) (medfly), obtained from three sweet orange varieties, lemon, and bitter oranges. These data were combined with immature developmental rates and survival on the same hosts to estimate host‐specific population parameters. Pairs of newly emerged adults from each citrus variety were held individually in transparent plastic cages, and females were allowed to oviposit in either red domes (artificial, pre‐punctured plastic oviposition devices), or intact, whole citrus fruits. We found strong effects of larval host (citrus fruits) on adult longevity and fecundity. In all five citrus varieties, females did not manage to deposit eggs into fruit pulp. The proportion of eggs laid in either the flavedo or albedo area of the fruit peel differed depending on the citrus variety. In all cases except bitter oranges, females oviposited fewer eggs in citrus fruits than in the artificial oviposition substrates, suggesting that most citrus fruits cause a significant reduction in the reproductive potential of medflies. Negative correlations were found between fecundity and (a) the density of oil glands, and (b) the amount of essential oils in the flavedo area of citrus fruits. There was no correlation between fecundity and other fruit physical characteristics, such as resistance of fruit peel to pressure and thickness of the flavedo. Apparently, resistance of citrus fruits to medfly infestation is directly related to citrus essential oils. The intrinsic rate of increase (r) was higher in bitter oranges than in the three sweet orange varieties tested. A negative r was estimated for flies that developed and oviposited in lemons, indicating a tendency for population decrease in this host. The suitability of citrus fruits for medfly development and the practical implications of our findings for management of medflies in citrus orchards are discussed.