Effect of larval host food substrate on egg load dynamics, egg size and adult female size in four species of braconid fruit fly (Diptera: Tephritidae) parasitoids

Life history theory predicts that individuals will allocate resources to different traits so as to maximize overall fitness. Because conditions experienced during early development can have strong downstream effects on adult phenotype and fitness, we investigated how four species of synovigenic, larval-pupal parasitoids that vary sharply in their degree of specialization (niche breadth) and life history (Diachasmimorpha longicaudata, Doryctobracon crawfordi, Opius hirtus and Utetes anastrephae), allocate resources acquired during the larval stage towards adult reproduction. Parasitoid larvae developed in a single host species reared on four different substrates that differed in quality. We measured parasitoid egg load at the moment of emergence and at 24 h, egg numbers over time, egg size, and also adult size. We predicted that across species the most specialized would have a lower capacity to respond to changes in host substrate quality than wasps with a broad host range, and that within species, females that emerged from hosts that developed in better quality substrates would have the most resources to invest in reproduction. Consistent with our predictions, the more specialized parasitoids were less plastic in some responses to host diet than the more generalist. However, patterns of egg load and size were variable across species. In general, there was a remarkable degree of reproductive effort-allocation constancy within parasitoid species. This may reflect more “time-limited” rather than “egg-limited” foraging strategies where the most expensive component of reproductive success is to locate and handle patchily-distributed and fruit-sequestered hosts. If so, egg costs, independent of degree of specialization, are relatively trivial and sufficient resources are available in fly larvae stemming from all of the substrates tested.     

Intrinsic competition between Diachasmimorpha longicaudata and three native species of parasitoids (Hymenoptera: Braconidae: Opiinae) of Anastrepha (Diptera: Tephritidae) fruit flies under laboratory conditions

The effect of intrinsic competition between the exotic parasitoid Diachasmimorpha longicaudata (Ashmead) and the native species Doryctobracon crawfordi (Viereck), Utetes anastrephae (Viereck) and Opius hirtus (Fischer) (all Braconidae: Opiinae) was studied under laboratory conditions. Each native species and D. longicaudata acted as both a resident and an invader, and all species were introduced to the host simultaneously. Diachasmimorpha longicaudata was found to be the most competitive species because it achieved the highest parasitism percentage under all the experimental conditions, but it was also negatively affected by the presence and parasitic activity of the native parasitoids. Utetes anastrephae was the only species that maintained its parasitic rate when all species attacked the available hosts simultaneously. The emergence probability of a female D. longicaudata was positively associated with the increase in the number of scars on the cuticle of the host pupa, but this association was not observed for the native species. It was concluded that D. longicaudata is an intrinsic competitor that is superior to D. crawfordi, U. anastrephae and O. hirtus, whether acting as a resident or an invader, producing a female-biased sex ratio in all the evaluation conditions. Utetes anastrephae was the native species that was least affected by the competitive presence of D. longicaudata, which suggests that it could be used as a complementary biological control agent for Anastrepha fruit flies.     

Longevity of multiple species of tephritid (Diptera) fruit fly parasitoids (Hymenoptera: Braconidae: Opiinae) provided exotic and sympatric-fruit based diets

While adult parasitic Hymenoptera in general feed on floral and extrafloral nectars, hemipteran-honeydews and fluids from punctured hosts, Diachasmimorpha longicaudata (Ashmead), an Old World opiine braconid introduced to tropical/subtropical America for the biological control of Anastrepha spp. (Tephritidae), can survive on fruit juices as they seep from injured fruit. An ability to exploit fruit juice would allow such a parasitoid to efficiently forage for hosts and food sources simultaneously. Two New World opiines, Doryctobracon areolatus (Szepligeti) and Utetes anastrephae (Viereck), are also prominent Anastrepha parasitoids and are roughly sympatric. All three species were provided with: (1) pulp and juice diets derived from a highly domesticated Old World fruit (orange, Citrus sinensis L.) that is only recently sympatric with the Mexican flies and parasitoids and so offered little opportunity for the evolution of feeding-adaptations and (2) a less-domesticated New World fruit (guava, Psidium guajava L.), sympatric over evolutionary time with D. areolatus and U. anastrephae. Both sexes of D. longicaudata died when provided guava pulp or juice at a rate similar to a water-only control. D. areolatus and U. anastrephae, presumably adapted to the nutrient/chemical constituents of guava, also died at a similar rate. Survival of all three species on orange pulp and juice was greater than on water, and often equaled that obtained on a honey and water solution. In confirmatory experiments in Mexico, D. areolatus and U. anastrephae, as well as other tephritid parasitoids Doryctobracon crawfordi (Viereck) and Opius hirtus (Fisher), all died at a significantly higher rates when provided guava in comparison to a honey and water diet. Such a result is likely due to guavas being repellent, innutritious or toxic. D. longicaudata clearly consumed guava juice tagged with a colored dye. Dilutions of orange and guava juice resulted in shorter lifespans than dilutions of orange juice and water demonstrating that there while diluted orange juice provided nutrition the addition of guava created toxicity. Given the differences in fruit-food quality, adult opiine food sources would not be obtainable at all oviposition sites and in the case of guava, more additional sites and foraging for food than previously postulated may be required.     

Effect of continuous rearing on courtship acoustics of five braconid parasitoids,candidates for augmentative biological control of <Emphasis Type="Italic">Anastrepha</Emphasis> species

The courtship acoustics of five species of parasitoid wasps (Hymenoptera: Braconidae), potential candidates for augmentative biological control of Anastrepha (Schiner) species (Diptera: Tephritidae), were compared between recently colonized individuals and those continuously reared 70–148 generations. During courtship, males of these parasitoid species fan their wings and produce a series of low amplitude pulses. The first series of 15 or more continuous courtship pulses was used to measure the pulse duration, frequency, and interpulse interval (IPI) from the beginning, middle, and end of the pulse series. Each parameter was compared between young and old colonies, and among species. Several differences in courtship acoustics were detected in colonies that had been continuously reared. The pulse duration at the end of the pulse series was longer in old colonies for Doryctobracon crawfordi (Viereck) (Hymenoptera: Braconidae), but shorter for old colonies of Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae). The IPI of the middle pulse was shorter in old colonies of Opius hirtus (Fischer) (Hymenoptera: Braconidae), and was also shorter at the last pulse for old colonies of both Utetes anastrephae (Viereck) (Hymenoptera: Braconidae) and D. longicaudata. The duration of the middle pulse distinguished the three native species, and separated the two introduced species from each other. We discuss our findings in light of their biological and applied implications, particularly those dealing with quality control of mass-reared parasitoids.     

Intrinsic competition between resident and invasive parasitoids (Hymenoptera: Braconidae) that attack the West Indian fruit fly Anastrepha obliqua under field conditions

We evaluated under semi-field conditions the intrinsic competition between Diachasmimorpha longicaudata (Ashmead), as an invasive parasitoid, and Doryctobracon areolatus (Szépligeti) and Utetes anastrephae (Viereck) (all Hymenoptera: Braconidae) as resident parasitoids, as well as that between U. anastrephae as an invader and D. areolatus as a resident. The percentage of live D. areolatus larvae decreased by 39.8% and 29.4% following attack by D. longicaudata and U. anastrephae as invasive parasitoids, respectively. Likewise, the parasitism percentage of D. areolatus decreased by 31.5% and 60.8% under competition with the invasive parasitoids D. longicaudata and U. anastrephae, respectively. Parasitism by D. longicaudata decreased by 44.6% and 41.6% in the presence of the residents D. areolatus and U. anastrephae, respectively, while parasitism of U. anastrephae was only affected when this species was a resident. We concluded that D. areolatus is an inferior intrinsic competitor and that U. anastrephae resists the competitive presence of D. longicaudata.     

Anastrepha ludens (Loew) (Diptera: Tephritidae) larvae irradiated at higher doses improve the rearing of two species of native parasitoids

Irradiation doses 40, 80, 120 and 160 Gy were used on 6-, 7-, 8- and 9-days-old Anastrepha ludens (Loew) (Diptera: Tephritidae) larvae. The larvae from the different age groups irradiated with different doses were exposed separately to Neotropical-native Doryctobracon crawfordi (Viereck), Utetes anastrephae (Viereck) and the Asian introduced Diachasmimorpha longicaudata (Ashmead) parasitoids (Hymenoptera: Braconidae). A significant increment in parasitoid emergence directly related to radiation increment on parasitoids D. crawfordi and U. anastrephae was observed. This effect was higher on irradiated young larvae; in D. longicaudata, emergence increment was related to age of larva but not with radiation doses. Similar results were obtained for sex ratio. Host larva weight increased with age, and irradiation had no effect on gaining weight of growing larvae. The host larval mortality 72 hr after exposition had an inverse relationship regarding to its age, although it did not have a negative effect as regards radiation doses. Immature stages of parasitoid/larva (>1 = superparasitism) were higher in 8-days-old larvae parasitized by D. Longicaudata, while in D. crawfordi and U. Anastrephae, superparasitism was absent (<1 immature stage per host larva). Superparasitism was not affected by increased radiation dose. No levels of melanin were detected as indicators of immunological reactions. However, these results are considered to be closely related to the lessening of these reactions due to irradiation. The positive relationship between emergence and irradiation dose to host larvae was present in native species D. crawfordi and U. anastrephae, but absent for exotic D. longicaudata. The data presented here are of great relevance for cost effective mass rearing of these parasitoids.     

Choosy egg parasitoids: Specificity of oviposition-induced pine volatiles exploited by an egg parasitoid of pine sawflies

Generalist parasitoids are well‐known to be able to cope with the high genotypic and phenotypic plasticity of plant volatiles by learning odours during their host encounters. In contrast, specialised parasitoids often respond innately to host‐specific cues. Previous studies have shown that females of the specialised egg parasitoid Chrysonotomyia ruforum Krausse (Hymenoptera: Eulophidae) are attracted to volatiles from Pinus sylvestris L. induced by the egg deposition of its host Diprion pini L. (Hymenoptera: Diprionidae), when they have previously experienced pine twigs with host eggs. In this study we investigated by olfactometer bioassays how specifically C. ruforum responded to oviposition‐induced plant volatiles. Furthermore, we studied whether parasitoids show an innate response to oviposition‐induced pine volatiles. Naïve parasitoids were not attracted to oviposition‐induced pine volatiles. The attractiveness of volatiles from pines carrying eggs was shown to be specific for the pine and herbivore species, respectively (species specificity). We also tested whether not only oviposition, but also larval feeding, induces attractive volatiles (developmental stage specificity). The feeding of D. pini larvae did not induce the emission of P. sylvestris volatiles attractive to the egg parasitoid. Our results show that a specialist egg parasitoid does not innately show a positive response to oviposition‐induced plant volatiles, but needs to learn them. Furthermore, the results show that C. ruforum as a specialist does not learn a wide range of volatiles as some generalists do, but instead learns only a very specific oviposition‐induced plant volatile pattern, i.e., a pattern induced by the most preferred host species laying eggs on the most preferred food plant.     

Host plant affects pollen beetle (Meligethes aeneus) egg size

Abstract. In some herbivorous insect species, egg size is larger on low‐quality hosts than on high‐quality hosts and may be related to the prospect that larger offspring are more likely to survive on a poor host. Sizes of eggs laid by pollen beetles [Meligethes aeneus Fab. (Coleoptera: Nitidulidae)] were examined with insects confined on one of two different host plants that had previously shown differences in adult preference and larval performance. Individual females were also exposed sequentially to both the low‐quality host (Sinapis alba L.) and the high‐quality host (Brassica napus L.) and the size of their eggs was determined. Pollen beetles laid shorter eggs on low‐quality hosts both for different females on different host plants and for the same individuals on different host plants, in contrast to the prediction that low‐quality hosts would receive larger eggs than high‐quality hosts. Previously, egg production rate was shown to be reduced when pollen beetles are exposed to low‐quality hosts and it is suggested that oogenesis is incomplete, resulting in shorter eggs. The possibility that this is related to antibiosis on S. alba is discussed.     

The Distributions of Parasitoids (Hymenoptera) of Anastrepha Fruit Flies (Diptera: Tephritidae) along an Altitudinal Gradient in Veracruz, Mexico

In the state of Veracruz, Mexico, fruits from 38 sites at various altitudes were collected monthly over a period of 2 years, and the tephritid fruit flies of the genus Anastrepha and associated parasitoids that emerged from these fruits were identified and counted. Of the 26 species of fruits that contained Anastrepha larvae, 18 species also contained a total of 10 species of Anastrepha parasitoids. These consisted of 4 native and 1 exotic species of opiine braconid larval–pupal parasitoids, 2 native species of eucoilid larval–pupal parasitoids, 1 exotic species of eulophid larval–pupal parasitoid, 1 exotic species of pteromalid pupal parasitoid, and 1 native species of diapriid pupal parasitoid. Overall parasitism (including flies from fruit species that bore no parasitoids) was 6% and was greatest, 16%, at 600–800 m in altitude. The relative contributions of individual parasitoid species to overall parasitism were frequently influenced by both the altitude (and correlated changes in temperature and precipitation) and the species of plant in which the Anastrepha larvae were found. This was particularly the case among the more abundant and widespread Braconidae. To distinguish the role of altitude from that of the distributions of the host plants, these braconids were examined in 4 individual species of fruit that grew over a broad range of altitudes. In guava (Psidium guajava L.) and “jobo” (Spondias mombin L.) the parasitoid Doryctobracon areolatus (Szepligeti) was relatively more common at low altitudes. Its congener, Doryctobracon crawfordi (Viereck), was relatively more abundant at high altitudes in sour orange (Citrus aurantium L.). Utetes anastrephae (Viereck) became relatively more common at higher altitudes in S. mombin, whereas Diachasmimorpha longicaudata (Ashmead) tended to become relatively rare at the highest altitudes in C. aurantium, but increased at high altitudes in P. guajava compared to other braconids. Different altitudinal patterns of abundance in different fruits suggests the importance of both biotic and abiotic factors in parasitoid distributions. We discuss the effect of an expanding agricultural frontier on parasitoid abundance and relate our findings to the design of a fruit fly biological control program that tailors mass releases to parasitoid climate preferences.     

Does host determine short‐range flight capacity of trichogrammatids?

Biological traits, such as body size, fecundity and fertility, of egg parasitoids are strongly influenced by host species, and the use of a single‐host species for consecutive generations has been showed to be detrimental for egg parasitoid biology. Besides biological traits, behaviour of egg parasitoids is also an important parameter for implying their performance in the field, but information about the effect of host on the behaviour of egg parasitoids is still scarce. Thus, this work aimed at determining the influence of host species on the short‐range flight capacity of three egg parasitoids Trichogrammatoidea annulata De Santis, Trichogramma atopovirilia Oatman and Platner and Trichogramma bruni Nagajara reared on Anagasta kuehniella (Zeller), Corcyra cephalonica (Stainton) and Sitotroga cerealella (Olivier), for first, 10 and 28 consecutive generations. Trichogrammatids emerged inside a tubular dark flight chamber, under controlled conditions, and short‐range flying response was based on the proportions of adults trapped to the sticky top of the chamber and the ones found on the bottom, which were checked for defective wings. Our data clearly demonstrate that trichogrammatid short‐range flight depends on the fasctidious host species. All three egg parasitoids had their flight capacity significantly reduced when emerged from S. cerealella. The highest flying capacity of T. annulata was registered when reared on C. cephalonica, while for T. atopovirilia was on A. kuehniella and T. bruni on both C. cephalonica and A. kuehniella. Parasitoid flight capacity is affected when reared on the same host over generations; however, it was not possible to define a pattern for any of the trichogrammatids. Our findings are of great relevance for quality control of mass‐reared egg parasitoids because measuring only behavioural traits with use of flight chambers can be more practical and less time‐consuming than assessing biological parameters.     

Effects of a fruit and a host-derived compound on orientation and oviposition in Utetes anastrephae,a little studied opiine braconid (Hymenoptera) parasitoid of Anastrepha spp. fruit flies (Diptera: Tephritidae)

Augmentative biological control of tephritid fruit flies would benefit from: (1) synthetic attractants to monitor the survival and dispersal of released parasitoids and (2) synthetic oviposition stimulants to reduce production costs of parasitoid species that are now prohibitively costly to mass-rear. Utetes anastrephae (Viereck) is a widespread and sometimes common opiine braconid parasitoid of several pest Anastrepha spp. Despite its host range, distribution and abundance, it has attracted relatively little research and little is known of its chemical ecology. Its orientation was determined towards two chemical cues hypothesised to be useful at two spatial scales: (1) limonene derived from fruit is presumably abundant and widely dispersed and might identify from a distance patches of potentially host-containing fruit; and (2) para-ethylacetophenone (PEA), a volatile emitted by a number of tephritid larvae, presumably in relatively small amounts, and which could serve as short-range cue or oviposition stimulant. Various concentrations of limonene proved attractive to both females and males, perhaps to the later as a means of locating females accumulated in the vicinity of limonene-emitting host plants. PEA at the concentrations tested did not influence oviposition in U. anastrephae, although it did so for Diachasmimorpha longicaudata (Ashmead), another opiine tephritid parasitoid, previously known to respond to PEA and included in the experiment as a positive control. Limonene at the concentrations tested had no effect on oviposition in either species. These results advance efforts to synthesise attractants and oviposition stimulants for alternative candidates for augmentation such as U. anastrephae.     

Native parasitoids associated with the genusAnastrepha (Dipt.: Tephritidae) in Los Tuxtlas,Veracruz, Mexico

In this paper we record the native parasitoids associated withAnastrepha fruit flies collected in a native tropical community from Los Tuxtlas, Veracruz, Mexico. A total of 1600 puparia ofAnastrepha were recovered from infested fruits of ten different host plants. From these puparia we obtained 218 Hymenopteran parasitoids representing the following species:Doryctobracon areolatus (Szépligeti),Utetes (Bracanastrepha) aff.anastrephae (Viereck),Doryctobracon crawfordi (Viereck),Opius hirtus (Fischer),Microcrasis n. sp.,Nealiolus n. sp. (all Braconidae);Odontosema n. sp. andLopheucoila sp. (Cynipidae). The most abundant and frequently encountered parasitoid species observed during this study wasD. areolatus, representing 59.2% of all recovered parasitoids. The analysis of different infestation rates in fruits regarding to degree of parasitization in theseAnastrepha species suggest they are not correlated, meanwhile some host plant characteristics such as fruit size, could play an important role in influencing rates of parasitization.     

Egg load dynamics and the risk of egg and time limitation experienced by an aphid parasitoid in the field

Insect parasitoids and herbivores must balance the risk of egg limitation and time limitation in order to maximize reproductive success. Egg and time limitation are mediated by oviposition and egg maturation rates as well as by starvation risk and other determinants of adult lifespan. Here, we assessed egg load and nutritional state in the soybean aphid parasitoid Binodoxys communis under field conditions to estimate its risk of becoming either egg‐ or time‐limited. The majority of female B. communis showed no signs of egg limitation. Experimental field manipulations of B. communis females suggested that an average of 4–8 eggs were matured per hour over the course of a day. Regardless, egg loads remained constant over the course of the day at approximately 80 eggs, suggesting that egg maturation compensates for oviposition. This is the first case of such “egg load buffering” documented for a parasitoid in the field. Despite this buffering, egg loads dropped slightly with increasing host (aphid) density. This suggests that egg limitation could occur at very high host densities as experienced in outbreak years in some locations in the Midwestern USA. Biochemical analyses of sugar profiles showed that parasitoids fed upon sugar in the field at a remarkably high rate. Time limitation through starvation thus seems to be very low and aphid honeydew is most likely a source of dietary sugar for these parasitoids. This latter supposition is supported by the fact that body sugar levels increase with host (aphid) density. Together, these results suggest that fecundity of B. communis benefits from both dynamic egg maturation strategies and sugar‐feeding.     

Influence of egg load and host size on host-feeding behaviour of the parasitoid Aphytis lingnanensis

Abstract.

• 1 Direct behavioural assays were used to investigate the influences of host size and parasitoid egg load on the decision to host feed versus oviposit made by the parasitoid Aphytis lingnanensis Compere. Egg load was manipulated without concurrent influences on the history of host contact by exploiting size-related variation in fecundity and by holding parasitoids at different temperatures to vary the rate of oocyte maturation.
• 2 Host feeding comprised a series of feeding bouts, separated by renewed probing of the scale insect body. Successive feeding bouts were progressively shorter, suggesting that hosts represent ‘patches’ yielding resources at a decelerating rate.
• 3 Parasitoids were significantly more likely to host feed on smaller hosts and oviposit on larger hosts.
• 4 Neither egg load nor the treatment variables (parasitoid size and holding temperature) exerted significant influences on the decision to host feed versus oviposit on second instar (low quality) hosts.
• 5 The failure to observe an effect of egg load on host-feeding decisions was not simply a reflection of the parasitoids being entirely insensitive to egg load; significant effects of egg load on parasitoid search intensity and clutch size decisions were observed.
• 6 Parasitoids developing on second instar (low quality) hosts experienced high levels of mortality late during development and yielded very small adults.
• 7 The discord between these experimental results and predictions regarding the importance of egg load underscores the need for additional work on the proximate basis for host-feeding decisions and the nutritional ecology of insect parasitoids.

     

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.     

Effects of the mixed biocide Bacillus thuringiensis–abamectin on the development of the parasitoid Microplitis mediator and its host Helicoverpa armigera

The effects of the mixed biocide Bacillus thuringiensis Berliner with abamectin (BtA) on the development of the parasitoid Microplitis mediator (Haliday) (Hymenoptera: Braconidae) and its cotton bollworm host, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), were evaluated in the laboratory. Weight gain in larvae of H. armigera was initially delayed, but larval developmental period increased and pupal weight increased when they were fed on a diet containing BtA. Due to increased longevity of the host larvae, the susceptible period to parasitization of H. armigera by M. mediator increased when the host larvae were reared on diets containing BtA at concentrations of 0.5, 1, 2, and 4 μg g^?1. The longevity of female and male parasitoids significantly decreased when newly emerged wasps were fed a honey solution containing 200 μg ml^?1 BtA in comparison with those fed only a honey solution. Mean longevity was significantly prolonged when parasitoids were fed a honey solution and BtA–honey solution in comparison with those fed BtA–distilled water, distilled water, or nothing. There were no significant differences compared with the control in any biological characteristics for the offspring of female parasitoids fed the honey solutions containing BtA at concentrations of 50, 100, and 200 μg ml^?1; characteristics measured include the egg‐larval period, pupal weight, male and female pupal periods, adult fresh weight, and adult longevity. When female parasitoids parasitized host larvae that had been fed the diet containing BtA, their male and female pupal periods were significantly prolonged compared with the control (without BtA).     

Response of two parasitoid species (Hymenoptera: Braconidae,Figitidae) to tephritid host and host food substrate cues

The Neotropical‐native figitid Aganaspis pelleranoi (Brèthes) and the Asian braconid Diachasmimorpha longicaudata (Ashmead) are two parasitoids of Tephritidae fruit flies with long and recent, respectively, evolutionary histories in the Neotropics. Both species experienced a recent range of overlap. In Argentina, A. pelleranoi is a potential species in biological control programs against the pestiferous tephritid species, Anastrepha fraterculus (Wiedemann) and Ceratitis capitata (Wiedemann), whereas D. longicaudata is already used in open‐field releases against Medfly in central‐western Argentina. To characterize the host‐foraging strategies of A. pelleranoi and D. longicaudata, olfactometer experiments were conducted comparing responses to C. capitata and A. fraterculus larvae, in two kinds of food substrate: fruit and artificial larval medium. To control the possible influence of host larvae used for parasitoid rearing on olfactory response, two strains of both parasitoid species, reared on both tephrtid species, were studied. Volatiles directly emanating either from A. fraterculus or C. capitata larvae may be detected by both A. pelleranoi and D. longicaudata, although chemical stimuli originating from the combination of host larvae and the habitat of the host were preferred. However, olfactory cues associated with host larvae probably play a relevant role in host searching behaviour of A. pelleranoi, whereas for D. longicaudata, the host‐habitat olfactory stimuli would be highly essential in short‐range host location. The strain of the parasitoids did not affect host search ability on the two tephritid species evaluated. These evidences are relevant for mass production of both parasitoids and their impact following open‐field augmentative releases.     

Field collection of egg parasitoids of Pentatomidae and Scutelleridae in Northwest Italy and their efficacy in parasitizing Halyomorpha halys under laboratory conditions

The invasion of Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) has caused severe economic damage in crops in North America and Europe, motivating research to identify its natural enemies, both in native and invaded areas. In its Asian native range, the main natural enemies are egg parasitoids, among which the most effective are Trissolcus japonicus (Ashmead) and Trissolcus mitsukurii (Ashmead) (Hymenoptera: Scelionidae) in China and Japan, respectively. In Europe, biology, host range, and impact of most native scelionid species are not well‐known. The present study aimed to investigate (1) presence and abundance of scelionid species that parasitize native Pentatomidae and Scutelleridae eggs in Northwest Italy, and (2) their ability to develop on H. halys eggs. During 4‐year field surveys, egg masses were collected and reared until bug nymph or adult parasitoid emergence. Then, the obtained scelionid females were tested for their ability to parasitize H. halys eggs in laboratory no‐choice experiments. Egg masses of all collected bug species were parasitized, and Telenomus spp. (Hymenoptera: Scelionidae), Trissolcus belenus (Walker), and Anastatus bifasciatus (Geoffroy) (Hymenoptera: Eupelmidae) were the most common parasitoids. In the laboratory, Trissolcus kozlovi Rjachovskij was the only species to significantly produce offspring from fresh H. halys eggs, whereas all tested Trissolcus species significantly induced host egg abortion (non‐reproductive effects). This study provides knowledge of the parasitoid species associated with native bugs, and represents a starting point to investigate the intricate interactions between native and exotic parasitoids recently found in northern Italy. These egg parasitoids could potentially be effective biocontrol agents of H. halys.     

Food sources for adult Diachasmimorpha longicaudata, a parasitoid of tephritid fruit flies: effects on longevity and fecundity

We report the results of a study on potential food sources of the widely distributed Indo‐Australian braconid fruit fly parasitoid Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae). Adults sustained life on diets of fruit juice or fruit pulp, a homopteran and its associated honeydew, or extrafloral nectary secretions. Longevities on all these foods and fecundity on fruit juice were comparable to those achieved on the honey that is typically provided in mass‐rearing programs. Certain of the flower species Bidens alba (L.), Spermacoce verticillata L., Lobularia maritima (L.) Desv., Brassica nigra (L.), Lantana camara L., their nectar or pollen, provided a diet that resulted in longer maximum life spans than water alone. Unlike some tephritid flies, the braconid did not feed on fresh bird feces or leaf‐surface exudates. Feeding by D. longicaudata on wounded host fruits of tephritid flies suggests that adult parasitoids would not need separate forays for adult food and oviposition sites, as these occur in the same locations. We conclude that an inventory of adult foods may help target inundative releases of D. longicaudata and lead to improvements in diets used for mass rearing.     

Egg resorption behaviour by the solitary egg parasitoid Anaphes nitens under natural conditions

We investigated under outdoor conditions and inside a climate chamber: (i) whether Anaphes nitens Girault (Hymenoptera: Mymaridae), an egg parasitoid of the Eucalyptus snout beetle, Gonipterus scutellatus Gyllenhal (Coleoptera: Curculionidae), experienced egg resorption, and (ii) how various treatments (location, food, and/or host supply) and body size influenced egg load, egg resorption, fecundity, and longevity. One‐day‐old females were mated and randomly assigned to five groups: (A) honey + hosts, (B) water + hosts, (C) only honey, (D) only water, and (E) control females killed at emergence. We compared the egg load of the newly emerged females, which represent the control group (egg load = ovarian eggs present at emergence), with the lifetime egg load (i.e., ovarian eggs + emerged offspring + not emerged offspring) of the females with various host and diet treatments, by dissection of the ovaries to find evidence of egg resorption. All groups reared outdoors had fewer eggs than the control, while indoors there was no significant difference. Outdoors, starved but host‐provided wasps (B) experienced the highest reduction of the lifetime egg load (51%). Groups without access to food (B + D) resorbed more eggs than groups provided with honey (A + C). Females with honey and hosts (A) had the highest lifetime fecundity, but those with water and hosts (B) showed a higher daily realized fecundity. Host‐deprived females with access to food (C) attained the longest lifespan. Our results suggest that under stress conditions, such as low temperature and food shortage, A. nitens females practice egg resorption, probably to save energy.