Clutch size in frugivorous insects as a function of host firmness: the case of the tephritid fly Anastrepha ludens

Abstract. 1. Optimal clutch size theory predicts that individuals will oviposit the number of eggs that increases their fitness. In Anastrepha ludens Loew (Diptera: Tephritidae), females oviposit larger clutches in unripe (firm) fruits than in ripe (soft) fruits. The following hypotheses were tested: (1) Using fruit firmness as an indicator of fruit quality, A. ludens females vary the number of eggs per clutch every time they reach an oviposition decision. (2) Maximising offspring survival with respect to either unripe or ripe fruit requires placing large clutches in firm fruit and smaller clutches in soft fruit. 2. Agar spheres were used as artificial hosts. Three agar concentrations resulted in three degrees of firmness. Mango fruits Mangifera indica L. served as natural hosts. Ripe and unripe fruits were used to test soft and firm host conditions respectively. Females laid significantly larger clutches in the firmer artificial hosts than in the softer hosts. They also laid significantly more eggs in artificial hosts without sugar than in hosts with sugar. Firm (unripe) mangoes also received significantly larger clutches than soft (ripe) mangoes. 3. When an individual female was first presented with a firm artificial host, it laid a large clutch. If subsequently offered a soft host, the female laid a significantly smaller clutch. Finally, if again offered a firm host, clutch size was increased significantly. 4. Possible trade‐offs in offspring fitness were explored in ripe and unripe mangoes by measuring offspring egg‐to‐adult survival, pupal weight, mean adult longevity, and fecundity. Despite the fact that larval survival was greater in soft fruit than in firm fruit, parameters such as pupal weight, mean longevity, and fecundity of adults stemming from both fruit types did not differ significantly. 5. A probable trade‐off between high offspring mortality caused by host unsuitability and low offspring and adult mortality caused by parasitism and predation is discussed as the reason for the exploitation of sub‐optimal hosts.     

Behavioural plasticity in relation to egg and time limitation: the case of two fly species in the genus Anastrepha (Diptera: Tephritidae)

Reproductive opportunities in insects that deposit their eggs in discrete resource patches are frequently limited because the availability of oviposition substrates is often spatially and temporally restricted. Such environmental variability leads individuals to confront time‐ or egg‐limitation constraints. Additionally, species with different oviposition strategies (i.e. single egg layers vs clutch layers) commonly deal with different structural and ecological characteristics of larval host plants. To test the hypothesis that oviposition strategies such as laying eggs singly or in batches (clutches) are related to these constraints (i.e. egg vs time limitation), we compared the lifetime oviposition patterns of two closely related sympatric species of Anastrepha (Diptera: Tephritidae) with different oviposition strategies. We exposed five cohorts of A. obliqua and A. ludens females, over the course of their adult lifetimes, to three conditions of “habitat quality” (measured as host density per cage): unpredictable habitat quality (host density varied randomly from day to day between 1, 5, 15, 30 and 60 hosts/cage), low habitat quality (fixed density of one host/cage) and high habitat quality (fixed density of 60 hosts/cage).
Responses to host density conditions were strikingly different in the two species. (1) Frequency of host visits and oviposition events increased in A. obliqua but not in A. ludens when host densities increased. (2) Anastrepha ludens females accepted low quality hosts (i.e. fruits on which eggs had already been laid and were therefore partially covered with host marking pheromone) significantly more often than A. obliqua females did. (3) Females of A. obliqua adjusted their oviposition activity to variations in host density, whereas A. ludens females exhibited a constant oviposition pattern (i.e. did not respond to variations in host density). Based on the above, it is likely that in A. obliqua oviposition is governed by egg‐limitation and in A. ludens by time‐limitation constraints. We discuss the relationship between the oviposition strategies of each fly species and the fruiting phenology and density of their native host plants. We also address the possible influence of oogenesis modality and parasitism by braconid wasps in shaping oviposition behaviour in these insects.     

Attraction of Mexican Fruit Flies (Diptera: Tephritidae) to Grapefruit: Enhancement by Mechanical Wounding of and Experience with Grapefruit

Wild strain, mated, female Mexican fruit flies, Anastrepha ludens (Loew), with no prior experience with fruit (naive), were not attracted to grapefruit, a preferred cultivated host, in wind tunnel experiments. Naive, mated laboratory strain females were attracted. Prior experience with grapefruit increased attraction of both laboratory and wild strains. More females were attracted to fruit with peel damage than to undamaged fruit, indicating that fruit odor mediated attraction. More naive than experienced females attempted to oviposit on the sides of the wind tunnel. Experienced laboratory males, but not wild males or naive males, were attracted to grapefruit. Attraction and oviposition behavior of laboratory flies was greater than that of wild flies.     

Age and host effects on clutch size in the Mexican fruit fly, Anastrepha ludens

We document individual and age-specific variation in reproductive output and clutch size of Anastrepha ludens Loew. (Diptera: Tephritidae). The influence of host size, color, and density on clutch size are also examined. Individual and groups of flies were offered artificial hosts composed of agar spheres wrapped in Parafilm. The gross reproduction rate of individual flies was 1000 eggs/female and 165 clutches/female with a range of 1 to 40 eggs/clutch. Mean clutch sizes for these females ranged from 4.5 to 10.6 eggs/clutch. The number of eggs/clutch laid by females held in groups was highly correlated with host size, ranging from about 4.4 eggs/clutch in 2 cm diameter hosts to 12.7 eggs/clutch in 11 cm hosts. Host color, host density, fly density, and fly age did not affect clutch size. This study suggests that variation among females and host size are the principal determinants of clutch size in A. ludens.

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Résumé L'examen a porté sur l'influence du polymorphisme et des modifications dues à l'âge des mouches sur la fécondité et la taille des pontes de A. ludens Loew (Dipt. Tephritidae). L'étude a concerné aussi l'influence de la dimension, de la couleur et de la densité des hôtes sur la taille des pontes. Des mouches isolées ou par groupes ont reçu des hôtes artificiels formés de sphères d'agar enveloppées dans du parafilm. La fécondité brute de femelles isolées a été de 1000 oeufs/femelle et de 165 pontes/femelle, avec une variation de 1 à 40 oeufs/ponte. La taille moyenne des pontes des différentes femelles isolées s'étalait de 4,5 à 10,6 oeufs/ponte. Le nombre d'oeufs/ponte des femelles groupées était fortement liée à la dimension de l'hôte, s'étalant de 4,4 oeufs/ponte pour des hôtes de 2 cm de diamètre à 12,7 oeufs/ponte pour ceux de 11 cm de diamètre. Ni la couleur et la densité des hôtes, ni la densité et l'âge des mouches n'ont influé sur la taille des pontes. Ces résultats suggèrent que les variabilités du comportement des femelles et de la dimension des hôtes déterminent par priorité la taille des pontes de A. ludens.

     

Effect of marking pheromone on clutch size in the Mediterranean fruit fly

Abstract Using acridine orange to selectively stain eggs, we showed that wild-collected female Mediterranean fruit flies (Ceratitis capitata Wiedemann) laid fewer eggs per clutch in fruit previously infested with eggs than in uninfested fruit. This effect is apparently attributable to marking pheromone deposited by females after oviposition: clutch size on fruit infested with eggs but free of marking pheromone was not statistically different from that on uninfested fruit. Clutch size on uninfested fruit on which marking pheromone was artificially transferred was significantly lower than that on uninfested and untreated fruit. Marking pheromone had a comparable though not statistically significant effect on the clutch size of females originating from a strain maintained in the laboratory for several hundred generations.     

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.     

Fecundity and oviposition ofEucelatoria bryani, a gregarious parasitoid ofHelicoverpa zea andHeliothis virescens

We examined longevity, fecundity, and oviposition strategies ofEucelatoria bryani Sabrosky (Diptera: Tachinidae), a gregarious endoparasitoid ofHelicoverpa zea (Boddie) andHeliothis virescens (F.) (Lepidoptera: Noctuidae). Longevity of adult femaleE. bryani was not related to body size. In contrast to longevity, largerE. bryani females had greater potential fecundity than smaller females, as determined by the number of embryonated eggs present in the common oviduct. However, female parasitoid size did not affect primary clutch size (number of eggs deposited in a host). Because embryos in eggs located in the ovisac were larger than those located elsewhere in the common oviduct, maximum primary clutch size may be physiologically limited by the number of fully mature eggs a female has available at one time.E. bryani females adjusted primary clutch size in response to host size, for bothH. zea andH. virescens. This adjustment appears to be adaptive because females did not overexploit hosts by depositing more larvae than a host could support. Adult emergence was not related to host size. Although host weight positively influencedE. bryani progeny weight, increases in progeny size with host size were counterbalanced by increases in primary clutch size with host size.     

Mutual interference in the mass-reared fruit fly parasitoid,Diachasmimorpha longicaudata (Hymenoptera: Braconidae)

Diachasmimorpha longicaudata is a solitary endoparasitoid produced in Mexico for the biological control of Anastrepha fruit flies (Diptera: Tephritidae). We studied the effect of mutual interference among conspecific foraging females to better understand the parasitoid-host dynamics established in the mass-rearing system of this species. We used a constant host availability of 60 third instar larvae of Anastrepha ludens (per oviposition unit type Petri dish) that were individually exposed for 3 h to 1, 2, 4, 8, 10, 14, and 20 D. longicaudata females, seven days old without oviposition experience. The following parameters were evaluated: total number of attacked hosts (i.e., larvae with at least one oviposition scar), number of attacked hosts per female, adult emergence percentage, and female proportion. We also performed a second assay at mass-rearing level, contrasting the current proportion used in mass-rearing (~?two host larvae per female) with the alternative treatments (5 and 7.5 host larvae per female). Results showed that the density of females foraging on a patch exhibits an inverse relationship to the number of hosts attacked by one female. The highest values for adult emergence (73.4%), patch exploitation (94.6%), and female proportion (0.86) were obtained in the treatments with 7.5, 6, and 3 host larvae per female, respectively. Under mass-rearing conditions, we found that a lower density of females per cage (~?five larvae per female) reduced superparasitism levels without affecting adult emergence and the proportion of females. This suggests that the mass-rearing efficiency of D. longicaudata could be improved by reducing the density of foraging females.

     

Clutch size in a larval-pupal endoparasitoid

Clutch size decisions by Aphaereta minuta (Nees) (Hymenoptera: Braconidae), a polyphagous, gregarious, larval-pupal endoparasitoid, were studied under laboratory conditions. This parasitoid attacks larvae of Diptera inhabiting ephemeral microhabitats such as decaying plant and animal material. Females oviposit in young larval stages, but the eventual size of the host pupa determines host food availability for competing offspring. The size of the pupa can differ greatly between host species. We questioned how A. minuta females deal with this delay between the moment of oviposition and eventual host food availability, and whether they make clutch size decisions that benefit their fitness. It was shown that females indeed vary their clutch size considerably and in an adaptive way: (1) females lay larger clutches in larvae of host species that produce larger pupae, even when the larvae are the same size at the moment of oviposition, and (2) females lay larger clutches in larger larvae than in smaller larvae of the same host species. The latter seems functional as larvae parasitized at an older stage indeed developed into larger pupae compared to larvae parasitized at a younger stage. Furthermore, mortality of parasitized young host larvae was greater than that of both unparasitized larvae and parasitized older larvae. Under field conditions the risk of mortality of young host larvae is expected to be even higher due to the limited period of microhabitat (host food) availability, strong scramble type competition between the host larvae, and the longer period of being exposed to predation.     

Effects of Conspecific Presence on Arrival and Use of Hosts in Ceratitis capitata Flies

To reach a better understanding of the factors that affect Mediterranean fruit flies', Ceratitis capitata (Wiedemann) (medflies'), arrival at and use of hosts, we evaluated the alighting and boring propensity of sexually mature high-egg load medfly females that were grouped with conspecifics or held in isolation for 4 days prior to testing. To avoid confounding effects that may have been responsible for conflicting results in previous studies, we exposed groups of free-foraging females to odorless artificial fruit (parafilm-covered agar spheres) in a rotating cage containing small potted host trees and kept experimental intervention to a minimum. Our protocol involved releasing cohorts of 24 females in a patch containing only two such low-quality hosts. In such circumstances, grouped females preferred to alight in significantly greater numbers on artificial fruit occupied by conspecifics than on unoccupied hosts and displayed a significantly greater propensity to oviposit in fruit in the presence than the absence of conspecifics. We did not detect differences in egg load or body size between intruders and residents or between winners and losers of contests. We conclude that as in adaptive superparasitism, the presence of conspecifics may enhance the propensity of fruit-foraging medflies to alight on and use scarce low-quality hosts.     

Age-dependent clutch size in a koinobiont parasitoid

Abstract.  1. The Lack clutch size theory predicts how many eggs a female should lay to maximise her fitness gain per clutch. However, for parasitoids that lay multiple clutches it can overestimate optimal clutch size because it does not take into account the future reproductive success of the parasitoid.
2. From egg-limitation and time-limitation models, it is theoretically expected that (i) clutch size decreases with age if host encounter rate is constant, and (ii) clutch size should increase with host deprivation and hence with age in host-deprived individuals.
3. Clutch sizes produced by ageing females of the koinobiont gregarious parasitoid Microplitis tristis Nees (Hymenoptera: Braconidae) that were provided daily with hosts, and of females ageing with different periods of host deprivation were measured.
4. Contrary to expectations, during the first 2 weeks, clutch size did not change with the age of the female parasitoid, neither with nor without increasing host-deprivation time.
5. After the age of 2 weeks, clutch size decreased for parasitoids that parasitised hosts daily. The decrease was accompanied by a strong decrease in available eggs. However, a similar decrease occurred in host-deprived parasitoids that did not experience egg depletion, suggesting that egg limitation was not the only factor causing the decrease in clutch size.
6. For koinobiont parasitoids like M. tristis that have low natural host encounter rates and short oviposition times, the costs of reproduction due to egg limitation, time limitation, or other factors are relatively small, if the natural lifespan is relatively short.
7. Koinobiont parasitoid species that in natural situations experience little variation in host density and host quality might not have strongly evolved the ability to adjust clutch size.     

Postemergence Experience Affects Sex Ratio Allocation in a Gregarious Insect Parasitoid

We tested the hypotheses that postemergence experience with plants (“early adult learning”) modifies sex ratio and clutch size allocations of Cotesia congregata (Say) (Hymenoptera: Braconidae), a gregarious larval endoparasitoid of Manduca sexta L. (Lepidoptera: Sphingidae). Emerging wasps were exposed for 2–3 h to (a) one of two host plants (tomato or tobacco) or no plant, and (b) one of two novel plants (arugula or parsley) or no plant. Each female was permitted a single oviposition in a host offered with one of the two plant species 24 h later. Hosts were reared on laboratory diet before and after parasitization. Wasps exposed to either host plant allocated proportionately more females to hosts offered with the plant species experienced at emergence than wasps with the alternate species, but clutch sizes did not differ. Irrespective of plant species, wasps exposed to novel plants allocated proportionately more females to hosts than wasps without plant experience, and larger clutches to hosts offered with parsley than with arugula. Differential responses to host and novel plants suggest inherent recognition of host foodplants by C. congregata. Results demonstrate a direct effect of learning on reproductive potential.     

Larval feeding substrate and species significantly influence the effect of a juvenile hormone analog on sexual development/performance in four tropical tephritid flies

The juvenile hormone (JH) analog methoprene reduces the amount of time it takes laboratory-reared Anastrepha suspensa (Caribbean fruit fly) males to reach sexual maturity by almost half. Here, we examined if methoprene exerted a similar effect on four other tropical Anastrepha species (Anastrepha ludens, Anastrepha obliqua, Anastrepha serpentina and Anastrepha striata) reared on natural hosts and exhibiting contrasting life histories. In the case of A. ludens, we worked with two populations that derived from Casimiroa greggii (ancestral host, larvae feed on seeds) and Citrus paradisi (exotic host, larvae feed on pulp). We found that the effects of methoprene, when they occurred, varied according to species and, in the case of A. ludens, according to larval host. For example, in the case of the two A. ludens populations the effect of methoprene on first appearance of male calling behavior and number of copulations was only apparent in flies derived from C. greggii. In contrast, males derived from C. paradisi called and mated almost twice as often and females started to lay eggs almost 1 day earlier than individuals derived from C. greggii, but in this case there was no significant effect of treatment (methoprene) only a significant host effect. There were also significant host and host by treatment interactions with respect to egg clutch size. A. ludens females derived from C. paradisi laid significantly more eggs per clutch and total number of eggs than females derived from C. greggii. With respect to the multiple species comparisons, the treatment effect was consistent for A. ludens, occasional in A. serpentina (e.g., calling by males, clutch size), and not apparent in the cases of A. obliqua and A. striata. Interestingly, with respect to clutch size, in the cases of A. ludens and A. serpentina, the treatment effect followed opposite directions: positive in the case of A. ludens and negative in the case of A. serpentina. We center our discussion on two hypotheses (differential physiology and larval-food), and also interpret our results in light of the life history differences exhibited by the different species we compared.     

Host size,superparasitism and sex ratio in mass-reared <Emphasis Type="Italic">Diachasmimorpha longicaudata</Emphasis>, a fruit fly parasitoid

We analyzed the relationship among host size, superparasitism and sex-ratio in mass reared Diachasmimorpha longicaudata (Hymenoptera: Braconidae). Individual host pupae of Anastrepha ludens (Diptera: Tephritidae) were measured (length and width), and the number of oviposition scars per pupa was used as a reliable indicator of superparasitism. The probability of an emerging parasitoid being a female was positively associated with the number of oviposition scars on the host cuticle, but not with the host size. The number of scars per host pupae from which females emerged was slightly but significantly higher than in those pupae giving raise to males. In D. longicaudata, the influence of host size on sex allocation decisions of individual females seems to be overridden by the level of superparasitism, which itself was positively correlated with pupa length. This suggests that larger pupae could experience a higher number of ovipositions than their smaller counterparts, and that a high level of superparasitism may conduct to a female biased sex ratio. We discuss the relevance of these findings which could provide new elements (e.g., the manipulation of superparasitism) for optimizing the mass rearing of this parasitoid.     

Host discrimination modulates brood guarding behaviour and the adaptive superparasitism in the parasitoid wasp Trissolcus semistriatus (Hymenoptera: Scelionidae)

Because hosts utilized by parasitoids are vulnerable to further oviposition by conspecifics, host guarding benefits female wasps. The present study aims to test whether female adults regulate brood guarding behaviour by host discrimination in a solitary parasitoid Trissolcus semistriatus by presenting an intact or parasitized host egg mass to a female adult. Virgin females without oviposition experience have host discrimination ability, which enables them to adjust the number of eggs laid in the hosts. Mating experience increases superparasitism by female adults, whereas mated females achieve a higher discrimination ability as a result of oviposition experience and show a lower superparasitism rate. As expected, females exhibit brood guard after parasitizing an intact host egg mass, whereas those females visiting a previously parasitized host egg mass, do not. Because the survival of eggs in superparasitized hosts is relatively low, regulating brood guarding behaviour by host discrimination is adaptive for female wasps.     

Sex allocation and clutch size in the gregarious larval endoparasitoid wasp, Cotesia glomerata

The ability of the gregarious larval endoparasitoid Cotesia glomerata L. (Hymenoptera: Braconidae) to adjust progeny sex ratio and clutch size was investigated. The sex ratios (proportion of males) of field clusters were diverse, but many (70%) were female-biased. Nearly 10% yielded males only, suggesting a low percentage of unmated females in the field. In over half of the clusters containing females, the sex ratio was below 0.3. Superparasitism was common in the field, and females were believed to increase progeny sex ratio when attacking previously-parasitized hosts. However, in a single oviposition bout, sex allocation was not precisely controlled both in the field and laboratory. In the laboratory, the number of eggs laid in a day tended to decrease with increasing female age. For females which were offered two hosts per day and for those offered three hosts per day, this value became nearly the same several days after the start of oviposition. The total number of hosts which a female could parasitize during her lifetime was often less than 40. Some of the old females which attacked more than 40 hosts produced male-biased clutches; this was due to sperm depletion, because sperm remained viable throughout a female's lifetime. The amount of sperm used in a single oviposition bout seemed fixed and was not dependent on the number of eggs laid. Females with much oviposition experience did not produce new eggs to compensate for deposited eggs, and the efficiency of egg use (deposited eggs/total eggs) was more than 80%.     

Life-history, genotypic, and environmental correlates of clutch size in the Glanville fritillary butterfly

Abstract.  1. Glanville fritillary butterfly ( Melitaea cinxia ) females lay up to 10 clutches of 50–300 eggs in their lifetime. Clutch size is an important life-history trait as larval group size affects survival throughout larval development.
2. Two experiments were carried out in a large population cage in the field to investigate the life-history and environmental correlates of clutch size.
3. Clutch size decreased with the cumulative number of eggs laid previously, increased with both female body weight and the number of days between consecutive clutches.
4. Genotypic differences among females in the glycolytic enzyme phosphoglucose isomerase had a significant influence on clutch size, partly because females of particular genotypes were able to initiate oviposition earlier in the day and thereby take advantage of the most favourable environmental conditions for oviposition.
5. Factors influencing clutch size were partly different in two summers, indicating the modulating effect of prevailing environmental conditions on reproductive performance.     

Effect of physiological and experiential state ofBactrocera tryoni flies on intra-tree foraging behavior for food (bacteria) and host fruit

Summary Using caged host trees on which we manipulated food and oviposition sites, we investigated the foraging behavior of individually-releasedBactrocera tryoni (Diptera: Tephritidae) females in relation to state of fly hunger for protein, presence or absence of bacteria as a source of protein, degree of prior experience with host fruit, and quality of host fruit for oviposition. One aim was to evaluate whether it is immature or matureB. tryoni females that are responsible for initially inoculating host fruit surfaces with fruit-fly-type bacteria, the odor of which is known to attractB. tryoni females. We found that 3-week-old immature females provided with sucrose but deprived of protein from eclosion had a much greater propensity than 3-week-old protein-fed mature females to visit vials containing fruit-fly-type bacteria, irrespective of whether vials were associated with adjacent host fruit or not. In the absence of associated bacteria in vials, immature females had a much lower propensity than mature females to visit host fruit. In the presence of bacteria in vials, however, propensity of immature and mature females to visit fruit was about equal. Mature (but not immature) females were more inclined to visit fruit that ranked higher for oviposition (nectarines) than fruit that ranked lower (sweet oranges). Mature females that attempted oviposition during a single 3-min exposure period to a nectarine prior to release were much more likely to find a nectarine than were mature females naive to fruit or immature females with or without prior contact with fruit. Exposure to a nectarine before release did not affect the propensity of either mature or immature females to alight on an odorless visual model of a nectarine, however. As judged by numbers of leaves visited, protein-deprived immature females were more active than protein-fed mature females, irrespective of the sorts of resources on a tree. Together, our findings lead us to conclude that (1) the firstB. tryoni females to arrive on the fruit of a host tree and therefore inoculate the fruit with fruit-fly-type bacteria are unlikely to be sexually immature, but to be mature as a result of having earlier acquired protein elsewhere, (2) the odor of colonies of fruit-fly-type bacteria when associated with host fruit will attract protein-hungry but not protein-fed females, and (3) the odor of the fruit itself will attract mature females (especially experienced ones) but not immature females. These findings illustrate the value of considering jointly the state of a resource patch together with the physiological and experiential state of the individual when investigating the foraging behavior of an insect.     

<Emphasis Type="Italic">Fopius arisanus</Emphasis> oviposition in four <Emphasis Type="Italic">Anastrepha</Emphasis> fruit fly species of economic importance in Mexico

We studied the oviposition performance of Fopius arisanus (Sonan) (Hymenoptera: Braconidae) attacking eggs of four fruit flies of the genus Anastrepha Schiner (Diptera: Tephritidae) under laboratory conditions. The complete process of oviposition on an individual egg of Anastrepha ludens (Loew) lasts in average 85.4 ± 2.9 s, including a tremor (25.8 ± 1.03 s) observed in the middle of this process related to the egg’s descent. The average parasitism of A. ludens egg was 60.9 ± 7.5%, with only 1.2% of superparasitized eggs. During individual acts of oviposition, we noted that F. arisanus possesses a highly flexible ovipositor that curves easily as it searches for additional suitable eggs, which may be of particular benefit when a female finds large clutches of eggs. The individual oviposition of F. arisanus in host fruits attacked by Anastrepha spp. varies with the egg clutch size of each fruit fly species: A. serpentina laid the biggest egg clutches (21.3 ± 1.4), followed by A. ludens (14.2 ± 0.9), and A. striata (1.0 ± 0.0) (=A. obliqua). The time spent by F. arisanus in individual ovipositions was parallel to these findings, reinforcing the idea that F. arisanus attacks several eggs in each individual insertion of its ovipositor. Neither formal oviposition acts, nor adult emergences of F. arisanus were registered in A. obliqua. We discuss the potential of F. arisanus as natural enemy of fruit flies of the genus Anastrepha, and explore the eventual developing of its mass rearing. Handling Editor: Torsten Meiners.     

Effects of pre-adult and adult experience on host acceptance in choice and non-choice tests in two strains ofTrichogramma

The effect of adult learning through an oviposition experience, and pre-adult learning through development inside a host was investigated in two strains of an Australian egg parasitoid,Trichogramma nrivelae (Hymenoptera: Trichogrammatidae). Host response was measured in two types of laboratory preference tests. In single host tests, females reared on three lepidopteran hosts (Heliothis punctigera (Noctuidae),Papilio aegeus (Papilionidae), andHypolimnas bolina (Nymphalinae)) were presented host eggs individually, and allowed two ovipositions. Pre-adult experience affected host preference in only one strain, while acceptance of a host was increased in both strains when they had previously oviposited in this host species. An oviposition experience had a stronger effect on host preference than pre-adult experience. In choice tests, pairwise combinations of hosts were arranged in an alternating grid. The ratio of host acceptances to host contacts was computed for the whole test and up to the first oviposition. These indicated that effects of rearing host were weak or absent, but the host chosen initially had a strong effect on host preference. Relative size of the hosts had a strong effect on choice of the first host. The implications of learning inTrichogramma are discussed in relation to host preference testing procedures and the selection of candidate strains for mass rearing and inundative release.