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

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

Host specificity of the egg pupal parasitoid Fopius arisanus (Hymenoptera: Braconidae) in La Reunion

Fopius arisanus is a polyphagous parasitoid of Tephritidae, which has been recently introduced to La Réunion Island as part of a classical biological control programme. We carried out laboratory experiments to assess the host specificity of this parasitoid, initially reared on Bactrocera zonata, and then offered for parasitization the eight local tephritid pest species. Naive or experienced parasitoid females were given tephritid eggs in no choice tests. Fopius arisanus females parasitize all fly species but parasitism varies with host species. No adult wasps emerge from Bactrocera cucurbitae and the survival of this species is only slightly affected by parasitism. Dissections show that the late instars of this fly may eliminate the parasitoid by encapsulation. When developing on Ceratitis capitata, Ceratitis rosa, Dacus ciliatus, Dacus demmerezi, and Neoceratitis cyanescens, parasitoid survival rate ranges from 10 to 25%. Bactrocera zonata and Ceratitis catoirii are the best hosts, yielding parasitoid survival rates of more than 70% with no premature mortality. The egg-larval mortality of C. capitata, C. rosa, D. ciliatus, and N. cyanescens, and the pupal mortality of D. demmerezi, are significantly increased by parasitism. The size of emerging adults is affected by host species and is correlated to pupal weight. Bactrocera zonata would be a favorable host to support routine colonization of F. arisanus for mass production of this parasitoid.     

Oviposition response and development of the egg-pupal parasitoid Fopius arisanus on Bactrocera oleae, a tephritid fruit fly pest of olive in the Mediterranean basin

To date, information is wanting with regard to the use of new exotic parasitoids against olive fruit fly, Bactrocera (=Dacus) oleae (Gmelin) (Diptera: Tephritidae), a serious pest of olives Olea europaea L., in the Mediterranean basin. We investigated the oviposition response and developmental biology on B. oleae of Fopius (=Biosteres) arisanus (Sonan) (=Opius oophilus Fullaway) (Hymenoptera: Braconidae), an egg-pupal parasitoid of tephritid fruit flies, never tested before as a potential parasitoid of this host. Our results showed that olive fruits infested with B. oleae eggs exerted a relevant attraction to gravid F. arisanus and represented a stimulus for oviposition. Nevertheless they were not as attractive to female parasitoids as the Mediterranean fruit fly, Ceratitis capitata Wiedemann (Diptera: Tephritidae), eggs infested papaya fruits (Carica papaya L.). In our experimental conditions, F. arisanus completed development in B. oleae within 33 ± 1.7 days (males) and 35 ± 1.6 (females). Increases in host egg to female parasitoid ratios of 1:1, 5:1, 10:1 and 20:1 corresponded with decreases in the percentage of B. oleae parasitisation and host killing but corresponded also with increases in absolute parasitisation. Our findings are discussed in light of possibilities of utilising F. arisanus for biological control of olive fruit fly.     

Implications of host mortality on the economics of Fopius arisanus (Hymenoptera: Braconidae) mass rearing

Fopius (= Biosteres) arisanus (Sonan) (= Opius oophilus Fullaway) is an egg-pupal parasitoid of tephritid fruit flies. Our breakthrough in the development of a laboratory-adapted strain of F. arisanus facilitated insectary rearing of parasitoids in large numbers. First colonized in captivity in 1989, F. arisanus has been reared routinely on the oriental fruit fly, Bactrocera (= Dacus) dorsalis (Hendel), its natural host. Parasitization by F. arisanus results in the latent death of developing hosts. Host mortality data are presented in a life table to estimate cost of parasitization on the economics of F. arisanus mass rearing. Percent kills of 10, 32, and 76% exerted by F. arisanus on the egg, larval, and pupal stages of the rearing hosts, respectively, resulted in a mean parasitoid recovery of 23.6%. The production cost was estimated by integrating life table data with the costs of rearing supplies and materials and personnel-hours requirements. Production of 1 million parasitoid adults requires the exposure of 4.2 million B. dorsalis eggs (= propagation hosts). We estimated the cost of producing 1 million parasitoids to be $2,363.30 and identified the most expensive aspects of F. arisanus rearing. Recommendations for streamlining the rearing process to reduce costs are provided.     

Foraging Behavior and Patch Time Allocation by Fopius arisanus (Hymenoptera: Braconidae), an Egg-Larval Parasitoid of Tephritid Fruit Flies

This study quantitatively describes the host-searching behavior of Fopius arisanus (Sonan) (Hymenoptera: Braconidae), an important egg-larval parasitoid of tephritid fruit fly pests, on coffee berries infested with host eggs of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). We also investigate the parasitoid's response to local variation in host patch quality. The temporal pattern of behavioral organisation was examined by constructing an ethogram. The parasitoid spent over 90% of its foraging time in detecting and locating hosts after arriving on a host-infested fruit, and displayed a relatively fixed behavioral pattern leading to oviposition. Patch residence time increased in the presence of host-associated cues, following successful ovipositions, and with increasing size of host clutches per fruit, but decreased with each successive visit to the same host patch and with increasing availability of alternative host patches. The parasitoid females discriminated against previously parasitized hosts and spent significantly less time and searching effort on patches previously exploited by herself or by conspecific females. The effective host-searching behavior, perfect host discrimination ability, and success-motivated searching strategy shown by F. arisanus ensured a thorough exploitation of host resources by this parasitoid.     

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

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

Old and new host-parasitoid associations: parasitism of the invasive fruit fly Bactrocera invadens (Diptera: Tephritidae) and five African fruit fly species by Fopius arisanus,an Asian opiine parasitoid

Fopius arisanus (Sonan), a solitary koinobiont endoparasitoid of fruit flies, was introduced for testing and final release against the recently discovered species Bactrocera invadens Drew, Tsuruta and White in Africa. Laboratory experiments were conducted to assess host preference, host acceptability for oviposition, and physiological suitability of B. invadens and five other indigenous tephritid fruit fly species, namely, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), C. cosyra (Walker), C. rosa Karsch, C. fasciventris (Bezzi), and C. anonae Graham. Females of F. arisanus visited all host egg patches, but showed a stronger preference to eggs of B. invadens, which was also most accepted for oviposition. Successful development of parasitoid progenies varied greatly across hosts, with B. invadens yielding the highest parasitoid progeny and C. fasciventris yielding no F. arisanus progeny. Most of the parasitoid eggs laid in C. rosa and C. fasciventris were encapsulated. Sex ratio was not influenced by host species and it was female biased in all hosts that produced parasitoid progeny. Fopius arisanus was able to establish a new association with C. capitata, C. cosyra and to a lesser extent C. anonae. The results are discussed in the light of the potential use of F. arisanus as a biological control agent of B. invadens.     

<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.     

Host species and vegetable fruit suitability and preference by the parasitoid wasp Fopius arisanus

Parasitoids that oviposit in a concealed host inside a plant part need to be able to find both the plant and the host. Egg parasitoids of fruit‐infesting Tephritidae need to assess the oviposition site based both on the host egg and the infested fruit. Infestation by Tephritidae fruit flies threatens fruit and vegetable production. Management methods have been implemented including biological control, using Fopius arisanus Sonan (Hymenoptera: Braconidae). The parasitism by F. arisanus in three Tephritidae flies in vegetable fruits was investigated. Laboratory assays were conducted to assess the parasitoid's preference and survival. Zucchini, sweet pepper, and tomato were artificially infested with eggs of Bactrocera dorsalis Hendel, Ceratitis capitata Wiedemann, and Ceratitis cosyra Walker (all Diptera: Tephritidae), then exposed to mated naïve F. arisanus females in a 20:1 egg:parasitoid ratio. Parasitoid behavioral activities (resting, antennating, probing, ovipositing) were observed on the infested fruits. Parasitism rate was determined by dissection of fruit fly eggs under a stereomicroscope. Behavioral activities of F. arisanus differed between all the fruits when infested with B. dorsalis or C. cosyra eggs but differed only between some of the fruits when infested with C. capitata. Fopius arisanus preferred B. dorsalis over C. capitata and C. cosyra, with a parasitism rate 2× higher on B. dorsalis compared to the Ceratitis species. Preference for fruits was dependent on the infesting fruit fly. The emergence of F. arisanus was higher with B. dorsalis than with Ceratitis spp. Although B. dorsalis completed its development earlier than Ceratitis spp., host fly species did not affect the developmental time of F. arisanus. We discuss the significance of F. arisanus preference in relation to naturally occurring Tephritidae infestations. We also discuss whether some fruits might constitute a refuge for Tephritidae flies and whether this will affect the current biological control efforts against B. dorsalis.     

‘Males second’ strategy in the allocation of sexes by the parasitic wasp,Gryon japonicum

Summary Patterns of the sex ratio allocation of Gryon japonicum (Ashmead) (Hymenoptera: Scelionidae), a solitary egg parasitoid of Riptortus clavatus (Thunberg) (Heteroptera: Alydidae), were investigated in the laboratory, and the result was checked against the field data on the sex composition of the parasitoid. When five host eggs were presented simultaneously to each of the females of G. japonicum in a laboratory experiment, they had a strong tendency to lay a male egg in second host egg and female eggs in the others. However, when four host eggs were presented to each female more than 3 h after the completion of oviposition on a host egg, most of the females laid male eggs in the third oviposition, i.e. the second host eggs after the experimental interruption of oviposition. These results indicated that there was a mechanism for G. japonicum to produce a male egg in the second host egg in consecutive ovipositions, and that the mechanism was reset by more than 3 h intervals of oviposition. By this mechanism, G. japonicum is thought to produce the precise sex ratio in response to the size of a host egg batch. Field data on the size of a host egg batch and the sex composition of the parasitoid in a host egg batch supported this view.     

Reciprocal influences and costs of parasitism on the development of Corcyra cephalonica and its endoparasitoid Venturia canescens

Many endoparasitoids develop successfully within a range of host instars. Parasitoid survival is highest when parasitism is initiated in earlier host instars, due to age-related changes in internal (physiological) host defences. Most studies examining fitness-related costs associated with differences in host instar have concentrated on the parasitoid, ignoring the effects of parasitism on the development of surviving hosts that have encapsulated parasitoid eggs. A laboratory experiment was undertaken examining fitness-related costs associated with encapsulation of Venturia canescens (Hymenoptera: Ichneumonidae) eggs by fifth (L5) instar larvae of Corcyra cephalonica (Lepidoptera: Pyralidae). Growth and development of both host and parasitoid were monitored in C. cephalonica larvae containing 0, 1, 2, or 4 parasitoid eggs. Adult size and fecundity of C. cephalonica did not vary with the number of eggs per host. However, there was a distinct increase in host mortality with egg number, although most parasitoids emerged from hosts containing a single egg. The most dramatic effect on the host was a highly significant increase in development time from parasitism to adult eclosion, with hosts containing 4 parasitoid eggs taking over 2.5 days longer to complete development than unparasitized larvae. The egg-to-adult development time and size of adult V. canescens did not vary with egg number per host, as demonstrated in a previous experiment using a different host (Plodia interpunctella). The results described here show that there are fitness-related costs to the host associated with resistance to parasitism.     

Egg Size, Intrinsic Competition, and Lethal Interference in the Parasitoids Encarsia pergandiella and Encarsia formosa

Recent population dynamic theory predicts that disruption of biological control may occur when one parasitoid species' superiority in intrinsic competition is associated with a lower ability to find and exploit hosts (i.e., ability in extrinsic competition). One might expect such a trade-off, for instance, if parasitoids with larger (and fewer) eggs are more likely to prevail in intrinsic competition than species with smaller (and more numerous) eggs. We tested the idea that relative egg size could be used to predict the outcome of intrinsic competition in two closely related endoparasitoids, Encarsia pergandiella Howard and Encarsia formosa Gahan. Contrary to expectation, the parasitoid species with smaller eggs, E. pergandiella, prevailed in intrinsic competition, regardless of the order that hosts were exposed to the two species. In a literature survey, we found four studies of competing pairs of endoparasitoid species for which: (a) egg size estimates were available and (b) one species was consistently superior in intrinsic competition. In three of the four studies, the small-egged species prevailed in intrinsic competition, as we also found. Although E. formosa lost in intrinsic competition, this species negatively affected E. pergandiella's progeny production by host feeding on and killing hosts containing E. pergandiella eggs. E. formosa females also host fed on conspecific-parasitized hosts. As a mechanism of both intra- and interspecific interference competition, host feeding on parasitized hosts contradicts assumptions about the nature of interference competition in existing population dynamics models.     

Does superparasitism improve host suitability for parasitoid development? A case study in the Microplitis rufiventris-Spodoptera littoralis system

Superparasitism refers to the oviposition behavior of parasitoid females who lay their eggs in an already parasitized host. Recent studies have shown that allocation of additional eggs to an already parasitized host may be beneficial under certain conditions. In the present work, mortality of Microplitis rufiventris wasps was significantly influenced by both host instar of Spodoptera littoralis larvae at parasitism and level of parasitism. In single parasitization, all host instars (first through sixth) were not equally suitable. Percentage of emergence success of wasp larvae was very high in parasitized first through third (highly suitable hosts), fell to 60% in the fourth instar (moderate suitable) and sharply decreased in the penultimate (5th) instars (marginally suitable). Singly parasitized sixth (last) instar hosts produced no wasp larvae (entirely unsuitable), pupated and eclosed to apparently normal adult moths. The scenario was different under superparasitism, whereas supernumerary individuals in the highly suitable hosts were almost always killed as first instars, superparasitization in unsuitable hosts (4th through 6th) had significant increase in number of emergence success of wasp larvae. Also, significantly greater number of parasitoid larvae successfully developed in unsuitable hosts containing three wasp eggs than counterparts containing two wasp eggs. Moreover, the development of surplus wasp larvae was siblicidal in earlier instars and nonsiblicidal gregarious one in the penultimate and last “sixth” instars. It is suggested that the optimal way for M. rufiventris to deal with high quality hosts (early instars) is to lay a single egg, while the optimal way to deal with low quality hosts (late instars) might be to superparasitize these hosts.     

Encapsulation and hemocyte numbers in three lepidopteran stemborers parasitized by Cotesia flavipes-complex endoparasitoids

Determination of the potential and actual host range of a natural enemy is crucial before its importation and release for biological control. We studied some of the factors that are important in determining the physiological host range of insect parasitoids attacking lepidopteran hosts. Our experimental system consisted of novel host-parasitoid associations, with two New World pyralid stalk borers, Diatraea saccharalis and D. grandiosella; one Old World crambid borer, Ostrinia nubilalis as hosts; and three Old World microgastrine braconids, Cotesia chilonis, C. sesamiae, and C. flavipes as parasitoids. Experiments on the chronology of encapsulation of the parasitoid progeny by host hemocytes indicated that lepidopteran stemborers that are taxonomically, behaviorally and ecologically very similar differ in their ability to encapsulate a parasitoid species. D. saccharalis encapsulated C. flavipes sometimes, whereas D. grandiosella consistently encapsulated C. sesamiae and C. flavipes. C. chilonis was not encapsulated by either Diatraea host. If encapsulation occurred it did not start until four days after parasitization and continued during the following days. O. nubilalis was an unsuitable host for all three parasitoid species; parasitoid eggs were killed within 24 hours of parasitization. O. nubilalis had nearly twice as many hemocytes present in the hemolymph compared to the Diatraea species. In many of the host-parasitoid combinations, there was an initial increase of hemocyte number soon after parasitization, which was not due to mechanical damage at oviposition. There was no correlation between total numbers of hemocytes present in the host hemolymph and the observed encapsulation levels. By understanding the encapsulation response we may be able to make better predictions about the host range of a parasitoid species before its release as a biological control agent.     

Effect of <Emphasis Type="Italic">Fopius arisanus</Emphasis> oviposition experience on parasitization of <Emphasis Type="Italic">Bactrocera dorsalis</Emphasis>

Fopius arisanus (Sonan) (Hymenoptera: Braconidae) is an important fruit fly parasitoid, successfully introduced in programs of classical biological control around the world. One aspect of its reproductive biology that has received increasing attention is the role of learning on parasitization by individual females. In this study, we examined the effect of previous oviposition opportunities on the reproductive success and progeny sex ratio of F. arisanus on eggs of Bactrocera dorsalis Hendel (Diptera: Tephritidae). Our results indicate that the proportion of eggs parasitized and parasitoid yield both increase with increasing experience, as acquired by individual females via previous oviposition opportunities. These effects are shown to be unrelated to parasitoid age out to three weeks, which we found not to have an effect on parasitization, yield, or sex ratio. We discuss the implications of our results on mass rearing and also in terms of the efficiency of this biological control agent in the field.     

Influence of initial egg density and host size on the development of the gregarious parasitoid <Emphasis Type="Italic">Bracon hebetor</Emphasis> on three different host species

Bracon hebetor (Say) (Hymenoptera : Braconidae) is a gregarious parasitoid that attacks a variety of important lepidopterous pests of stored product and in the field. In this study the effect of host species, size and larval competition on parasitoid size, survival and development were investigated. In laboratory studies, wasp eggs at a range of densities, were placed on larvae of different weight of three Lepidoptera host species namely Adoxophyes orana (Fischer von Röslerstamm, Tortricidae), Plodia interpunctella (Hubner, Pyralidae) and, Lobesia botrana(Dennis & Schiffermueller, Tortricidae). On A. orana survival of immature parasitoids was very low at all densities and different host weights. On L. botrana survival progressively reduced as egg density increased at both host weights examined for this host. Survival on P. interpunctella was significantly affected by egg density but not by host weight. Initial egg density had a significant effect on the size of emerging adults from each rearing host. Smaller adult parasitoids emerged as egg density per larva increased. Larval host weight of P. interpunctella and A. orana had a significant effect on the size of emerging adult parasitoids mainly at the higher egg densities used in these experiments. The above results of host quality on fitness of parasitoid are discussed.     

Comparison of Foraging Behavior, Interspecific Host Discrimination, and Competition of Encarsia formosa and Amitus fuscipennis

The foraging behavior of Amitus fuscipennis MacGown & Nebeker and Encarsia formosa Gahan was studied on tomato leaflets with 20 Trialeurodes vaporariorum (Westwood) larvae in the first or third stage. Ten of the whitefly larvae were previously parasitized and contained a conspecific or a heterospecific parasitoid egg or larva. The host type (host stage and/or previous parasitization) did not influence the foraging behavior of either parasitoid species. The residence time on these tomato leaflets was about 0.9 h for A. fuscipennis and 1.9 h for E. formosa. Amitus fuscipennis hardly stood still and fed little, while E. formosa showed extensive standing still and feeding. As a result, the time walking while drumming was similar for both parasitoid species. The numbers of host encounters and ovipositions per leaflet were similar for both parasitoid species. However, the residence time of A. fuscipennis was half as long as that of E. formosa so the rate of encounters and ovipositions was higher for A. fuscipennis. Amitus fuscipennis is more efficient in finding and parasitizing hosts under these conditions. The walking activity and host acceptance of the synovigenic E. formosa diminished with the number of ovipositions, but not those of the proovigenic A. fuscipennis. Encarsia formosa is egg limited, while A. fuscipennis is time limited because of its short life span and high egg load. Both parasitoid species discriminated well between unparasitized larvae and self-parasitized larvae, but discriminated poorly those larvae parasitized by a conspecific and did not discriminate larvae parasitized by a heterospecific. Self-superparasitism, conspecific superparasitism, and multiparasitism were observed for both parasitoid species. Superparasitism always resulted in the emergence of one parasitoid and multiparasitism resulted in a higher emergence of one parasitoid of the species that had parasitized first. The data suggest that A. fuscipennis is a good candidate for use in biological control of high-density spots of T. vaporariorum when we consider its high encounter and oviposition rate.     

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

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

Response ofChelonus blackburni [Hym.: Braconidae] to different ages and densities of potato tuber moth eggs

The response of an efficient egg-larval parasitoidChelonus blackburni Cameron to different ages and densities of potato tuber mothPhthorimaea operculella (Zeller) eggs was studied in a laboratory system. The parasitoid accepted 0–1, 1–2 and 2–3 day old eggs for parasitization. However, the eggs belonging to the first two age groups were significantly more acceptable when compared to the last age group. At low host density levels of 2 and 5 eggs per parasitoid, parasitoid emergence was zero. On increasing the host density, percent progeny production increased till a plateau was reached at a parasitoid-host ratio of 1∶50. This ratio thus proves to be ideal for obtaining maximum percent progeny production in the case of 0–1 and 1–2 day old eggs. Further increase in host density did not result in any significant increase in percent progeny production.      

Influence of the egg parasitoidPlatytelenomus busseolae [Hym.: Scelionidae] on the population ofSesamia nonagrioides [Lep.: Noctuidae] in central greece

The egg parasitoid,Platytelenomus busseolae (Gahan) (Hymenoptera: Scelionidae) was recorded from egg masses of the corn stalk borer,Sesamia nonagrioides (Lefebvre) (Lepidoptera: Noctuidae) on maize in the area of Istiaea, Central Greece. Natural parasitism was studied during the years 1986, 1987. A total of 3,382 egg masses, containing 205,227 eggs, was collected from corn fields. Parasitized eggs were found from end July to mid-October. In 1986. 76.2% of the egg masses and 42.8% of all eggs were parasitized, while in 1987, respective values were 27.6% and 12.9%. The inferior performance of the parasitoid in 1987 may be due to the unfavorable winter and summer conditions. Parasitism decreased when the host population was at its peak, but it increased again within 1 to 3 weeks. A small percentage of egg masses was completely parasitized (9.5% and 4.7% for the 2 years respectively). In 1987, the sex ratio, ♀♀/♂♂ was 1.5: 1 and 26.2% of the egg masses produced only ♂♂. Mated ♀♀ produced 3 times more ♀♀ than ♂♂. It seems that the parasitoid, under favorable weather conditions, can play a significant role in the control of the corn stalk borer.