Winter ecology of the cabbage aphid Brevicoryne brassicae (L.) (Homo., Aphididae) and its parasitoid Diaeretiella rapae (McIntosh) (Hym., Braconidae: Aphidiidae)

Abstract:  Flower strips near crops may stimulate natural enemies by the provision of nectar and hibernation sites. However, these habitats may also be beneficial for potential pest species. We investigated the dynamics of the cabbage aphid Brevicoryne brassicae (L.) (Homo., Aphididae) and its primary parasitoid Diaeretiella rapae (McIntosh) (Hym., Braconidae) in brussels sprout fields and adjoining flower plots in winter. A wide variety of 14 plant species were included in the study, each established as monoculture plots. Brussels sprout fields and flower plots were established at two sites. One site was located in an open agricultural landscape, the other in a landscape dominated by mixed forest. Brevicoryne brassicae and D. rapae were found on brussels sprout plants but not in the flower plots. Brevicoryne brassicae was initially more abundant in the open landscape, but as their densities declined rapidly in time, no living aphids were recovered at both sites by February. The density of aphids parasitized by D. rapae showed a similar trend, but densities of eight mummies per brussels sprout plant were still present by the end of February. These findings suggest that (i) flower species under investigation do not function as sources of B. brassicae and (ii) brussels sprout plants that are not harvested may not only harbour D. rapae populations that may sustain biological control, but are also likely to act as sources of B. brassicae infestation.     

Reproduction of Diaeretiella rapae on Russian wheat aphid hosts at different temperatures

Diaeretiella rapae (M'Intosh), a polyphagous and cosmopolitan parasite of aphids, was imported from China to the USA for biological control of Diuraphis noxia (Mordwilko), a pest of small grains. We studied several aspects of its biology on D. noxia hosts in the laboratory at 3 constant temperatures, 10.0, 21.1, and 26.7 °C. Females lived significantly longer than males at all 3 temperatures, and longevity was greatest at 10 °C, followed by 21.1 and 26.7 °C. Fecundity (= number of mummies) did not differ significantly among the 3 temperatures studied. The ovarian egg-load was 129.1 ± 9.3, and was significantly affected by the size of adult females. A pre-oviposition period ± 0.26 days) was detected at 10 °C, but not at the other temperatures. Pre-imaginal survivorship was similar among temperatures, while R _o and T _c decreased with temperature, and r _m increased with temperature. The offspring sex ratio (proportion females) was lowest at 26.7 °C, and similar between 10.0 and 21.1 °C. In addition, the offspring sex ratio significantly declined with the age of the female parent. The suitability of D. rapae for colonization against D. noxia in North America is discussed in relation to its responses to temperature and the climate of its home range.     

Overwintering strategies and cold hardiness of two aphid parasitoid species (Hymenoptera: Braconidae: Aphidiinae)

The role of winter diapause in two aphid parasitoid species, Aphidius ervi Haliday and Aphidius rhopalosiphi DeStefani-Peres (Hymenoptera: Braconidae: Aphidiinae), in host synchronization and the induction of cold hardiness was investigated. Parasitoids were reared during three successive generations on Sitobion avenae Fabricius, at 15 degrees C under a photoperiod of 9 h light 15 h dark. Although these conditions are known to be strongly diapause inducing, neither parasitoids showed an incidence of diapause above 65% over the three generations; the rest of the population underwent quiescence. In both parasitoid species, diapausing mummies exhibited greater cold hardiness than non-diapausing mummies, resulting in significantly lower supercooling points (SCP) and in a higher survival rate during long-term exposures at 0 and -10 degrees C. The induction of increased cold hardiness in parasitoids was thus associated with the diapause state. SCPs of third instar larvae of S. avenae were similar to those of non-diapausing mummies of both parasitoid species, but significantly higher than those of diapausing mummies. The effect of winter climate on the stability of the host-parasitoid interaction is discussed.     

Morphologische untersuchungen an antennen und komplexaugen von Diaeretiella rapae (Aphidiidae,Hymenoptera)

Differences in the morphology of antennae (especially sensillae) and compound eyes (number of ommatidia) of both sexes are described.     

Interference competition between Aphidius matricariae and Praon volucre (Hymenoptera: Braconidae) attacking two common aphid species

Interference competition is a common phenomenon that occurs among adult females of different species to gain the highest food resources at the same time. In this research, extrinsic competition between Aphidius matricariae and Praon volucre on different densities and stages of two important pests of greenhouse crops in the world, Aphis gossypii and Myzus persicae, were investigated. The results of this study showed that total percentage parasitism of second, third and fourth nymphal instars of A. gossypii and M. persicae by A. matricariae, and P. volucre were affected by extrinsic competition. A combination of A. matricariae and P. volucre on A. gossypii had a negative effect on performance of these parasitoids. Although extrinsic competition reduced the efficiency of A. matricariae and P. volucre on M. persicae, total parasitism of M. persicae by A. matricariae and P. volucre (combination of two parasitoids) increased compared to A. matricariae or P. volucre acting alone. Also the results indicated that the extrinsic competition between A. matricariae and P. volucre on both A. gossypii and M. persicae was apparently more intense when presented with 25 hosts compared to 50 and 100 hosts. The results of this research show important information to determine an appropriate combination of these two parasitoid wasps for biological control of A. gossypii and M. persicae in greenhouses.     

Sub-lethal Effects of the Insecticides Pirimicarb and Dimethoate on the Aphid Parasitoid Diaeretiella rapae (Hymenoptera: Braconidae) When Attacking and Developing in Insecticide-Resistant Hosts

The effectiveness of parasitoids as biological control agents can be constrained by insecticide use, not only through direct mortality but also as a result of sublethal effects. Several pest aphids have become resistant to a range of insecticides and a resistant strain of Myzus persicae was used in laboratory experiments to investigate sublethal effects of the insecticides pirimicarb and dimethoate on the parasitoid Diaeretiella rapae . Both insecticides produced sublethal effects on D. rapae when the parasitoid attacked and developed in aphids that had been dipped in insecticide solutions. Dimethoate affected oviposition behaviour; females were apparently repelled by residues on the surface of dipped aphids, thus reducing their attack rate and hence the number of mummies produced. Also, the reproductive performance of parasitoids that had developed in pirimicarb-dipped aphids appeared to be adversely affected, in comparison with parasitoids that emerged from uncontaminated hosts, and this was reflected both in lower mummy production and lower attack rates. Pirimicarb, but not dimethoate, affected the sex ratio of the offspring of D. rapae that had developed in dipped aphids, causing a significant increase in the proportion of males. This only occurred when the male parent had developed in a pirimicarb-dipped aphid, suggesting that the effect involves male sterility or mating behaviour, although they appeared to mate normally. These sublethal effects are potential constraints on the efficiency and effectiveness of D. rapae as a biological control agent of aphid pests, but to assess fully their potential impact further studies need to be done using more realistic extended laboratory and semi-field techniques.     

Host instar suitability of Aphis gossypii (Hemiptera: Aphididae) for Lysiphlebus testaceipes (Hymenoptera: Braconidae) and parasitism effect on aphid life table

Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae, Aphidiinae) has constituted a well-studied parasitoid insect model, but very little is known about the host-instar suitability of aphid for the wasp so far. One of the hosts of L. testaceipes is Aphis gossypii Glover (Hemiptera: Aphididae). The latter is a serious aphid pest to vegetable production in Benin. Therefore, the objectives of our study were to: (1) examine the oviposition behavior of L. testaceipes on A. gossypii; (2) investigate the host-instar suitability of A. gossypii for L. testaceipes; and (3) compare the life table parameters of A. gossypii with aphids parasitized by L. testaceipes and unparasitized aphids (control). The study was conducted in a laboratory at 26 ± 1 °C in petri dishes and revealed that the parasitoid utilized up to seven stabbing stings to handle and oviposit, particularly in older A. gossypii. In aphids parasitized at the third instar, the net reproductive rate R _o as well as the intrinsic rate of natural increase r _m was significantly lower (2.119 ± 0.272 and 0.110 ± 0.018) compared to the control (15.529 ± 1.287 and 0.272 ± 0.008), respectively (p < 0.01).     

Functional responses of aphid parasitoids,Aphidius colemani (Hymenoptera: Braconidae) and Aphelinus asychis (Hymenoptera: Aphelinidae)

We evaluated the functional responses of two aphid parasitoids: Aphidius colemani on the green peach aphid Myzus persicae (Hemiptera: Aphididae), and Aphelinus asychis on M. persicae and the potato aphid, Macrosiphum euphorbiae (Hemiptera: Aphididae). Parasitoid oviposition occurred at host densities of 5, 10, 20, 30, 50, 80 or 100 aphids for A. colemani and 5, 10, 20, 30 or 50 aphids for A. asychis. More M. persicae were parasitized by A. colemani than by A. asychis at an aphid density of 50. Among the three types of functional response, type III best described the parasitoid response to the host densities both in A. colemani and A. asychis. The estimated handling time was shorter for A. colemani than for A. asychis (0.017 and 0.043 d, respectively). The proportion of aphids that were parasitized exhibited the same characteristic curve among the three host-parasitoid combinations: a wave form that appeared to be a composite of a decelerating (as in type II) response at low host density and an accelerating-and-decelerating (as in type III) response at medium to high host density. We hypothesize that the novel host species (and its host plant), density-dependent superparasitism, and/or density-dependent host-killing may have induced the modified type III response.     

Comparison of artificial diets for rearing Bracon hebetor Say (Hymenoptera: Braconidae)

The ectoparasitoid Bracon hebetor Say is an insect frequently found in storage facilities, where it attacks stored grain pests. The biology of this parasitoid was studied when reared on seven different artificial diets (in vitro rearing), under controlled temperature (25 ± 2 °C), relative humidity (60 ± 10%), and photoperiod (14-h photophase), and compared to its biology on its natural host Anagasta kuehniella (Zeller) (in vivo rearing). The artificial diet contained 60% holotissue of Diatraea saccharalis (Fabricius) pupae, 12% fetal bovine serum, 12% lactoalbumin hydrolysate, and 16% egg yolk, enabled development similar to that obtained on the natural host. The life cycle duration (egg–adult) was not significantly different, and the adults reared on this diet promptly paralyzed and parasitized the natural host, though at a lower proportion than those reared in vivo. There was no difference in the longevity of females obtained with these two different rearing systems (in vivo and in vitro). However, about 60% of the larvae developed on the diet failed to produce a protective cocoon during the pupal phase, indicating a sub-optimal quality associated with this artificial medium.     

Host foraging for differentially adapted brassica-feeding aphids by the braconid parasitoid Diaeretiella rapae

Interactions occurring in a tritrophic system comprising plants, aphids and parasitoids are of great complexity. The generalist endoparasitoid Diaeretiella rapae (McIntosh) (Hymenoptera: Aphidiidae) displays specialist characteristics on brassica feeding aphids. Previously, we studied differential signalling to D. rapae by specialist and generalist Brassicaceae feeding aphids on turnip. We reported no differences in the attractiveness of volatile compounds from the two turnip/aphid complexes. However, we reported a significantly greater D. rapae attack rate on the specialist Lipaphis erysimi (Kaltenbach) than the generalist Myzus persicae (Sulzer). As a consequence we predicted that D. rapae would forage more efficiently and produce more offspring on L. erysimi. We present here some additional data collected in a more complex spatial/temporal environment in large experimental chambers and discuss this, drawing attention to the need for careful interpretation of mechanistic information in predicting the overall foraging process.Key words: tritrophic interactions, honeydew, Lipaphis erysimi, Myzus persicae, specialist, generalist, glucosinolatePlants are a principal component of parasitoid-host interactions.¹ Plant derived chemical cues may be exploited by parasitoids to locate successfully host habitats, hosts and to assess host quality either positively or negatively.² However, there are a multitude of other direct and indirect interactions that structure aphid-parasitoid communities.³ Plants of the family Brassicaceae have a diverse and interesting secondary chemistry, which forms an important component of their defence against herbivores. This secondary chemistry includes glucosinolates located within plant cells, which upon damage are hydrolysed by enzymes known as myrosinases.^4,5 Products of these reactions include nitriles and volatile isothiocyanates. Lipaphis erysimi (Kaltenbach), the turnip aphid, is a specialist on plants of the order Capparales, particularly the Brassicaceae, and like its fellow specialist, Brevicoryne brassicae,⁶ sequesters glucosinolates using them as defence against natural enemies,⁷ whereas Myzus persicae (Sulzer), the peach-potato aphid, does not sequester glucosinolates⁷ but excretes large quantities in its honeydew.⁸ We hypothesised that Diaeretiella rapae (McIntosh) would display different foraging behaviours toward plant-derived chemical signals from these differentially adapted aphids feeding on turnip.We have studied some of the behavioural responses of D. rapae to these two aphid species on a single cultivar of turnip (Brassica rapa var rapifera cv Tokyo Cross). Volatile compounds from turnip infested by L. erysimi or M. persicae are both attractive to D. rapae, but not differentially so. The volatile composition of both turnip/aphid complexes (TAC) includes two isothiocyanates, of which one, 3-butenyl isothiocyanate, was shown to be attractive in Y-tube bioassays.⁷ In no choice tests, attack rates, defined as the number of full contacts between the ovipositor of a parasitoid and its potential aphid hosts in a minute (counting multiple stabbings repetitively on the same aphid as one attack), were significantly greater on L. erysimi than on M. persicae, irrespective of which of these aphids was the original host.⁹ This is possibly due to glucosinolate derived kairomones that may be detected either by antennation or ovipositor probing on the potential host.¹⁰ This behaviour is primed by cues received by the parasitoid during emergence from its mummy case.⁹ Taking these mechanistic results together, we hypothesised that given an equal supply of potential hosts, D. rapae would parasitize more L. erysimi aphids than M. persicae, irrespective of the host in which they developed.We tested this hypothesis in four Perspex chambers (L 1.7 m, W 1.2 m, H 1 m) with each containing four potted turnip plants infested with 250 L. erysimi aphids and four with 250 M. persicae aphids. Plants infested with the different aphid species were placed alternately within the chamber in two equally spaced parallel rows. A total of 15 naive D. rapae parasitoids were released from three points in each chamber. A total of four one-chamber replicates were made using D. rapae reared on L. erysimi and four with D. rapae reared on M. persicae. Eleven days after the release of parasitoids the number of mummified aphids on each plant was recorded.We found that D. rapae reared on L. erysimi produced significantly more mummies on L. erysimi than M. persicae, as we hypothesised. However, D. rapae reared on M. persicae produced significantly more mummies on M. persicae than L. erysimi (Fig. 1). This was contrary to our hypothesis. In addition, there were significantly more mummies produced by parasitoids reared on L. erysimi than those reared on M. persicae.Open in a separate windowFigure 1Average number of mummified aphids recovered per species (LE = Lipaphis erysimi; MP = Myzus persicae) per cage. * indicates a significant difference by t-test in the number of mummies produced on LE and MP, (t = 2.39, p = 0.048) and (t = 2.40, p = 0.048) for D. rapae reared on M. persicae and L. erysimi respectively.In an attempt to identify possible reasons for these observations we recorded different aphid patch parameters for M. persicae and L. erysimi including patch area, aphids per patch and patch density. M. persicae formed larger less dense patches than L. erysimi (Fig. 2). As well as forming different patch structures the aphids are different in colour, M. persicae being generally yellow, while L. erysimi are a dark grey/green. Green and yellow pigments reflect distinctly different spectra of light, which can be detected by the trichromatic vision common to most hymenoptera.¹⁰ Thus colonies of the different species present different visual cues, which may provide essential foraging cues to parasitoids.^11,12 However, it seems unlikely that the parasitoids used in this experiment, naive but for the conditioning received upon emergence from their mummy case, would display different responses to visual cues. We propose that the chemistry of the system is likely to hold the key to the behaviour of D. rapae, and put forward the following explanation.Open in a separate windowFigure 2Aphid patch parameters, including patch area (cm²), number of aphids per patch, and density of aphids within the patches (Aphids/cm²) for Lipaphis erysimi (LE) and Myzus persicae (MP).D. rapae does not have a preference for the volatile compounds associated with either TAC. So, though not necessarily random, it is probable that there is an equal chance of encountering each aphid species first. It is evident that one of the main differences between the two TAC is the chemical constituents and quantity of honeydew, which has been shown to alter on-plant foraging for B. brassicae by D. rapae.^13–15 The honeydew composition of aphids is species and plant specific¹⁵ and has been shown to provide parasitoids with information on host species identity through species-specific kairomones.¹⁷ M. persicae feeding on the Brassicaceae produce a honeydew rich in glucosinolates.⁸ A likely consequence is that the cuticle of the M. persicae mummy case will retain some of this chemistry which will then be received by the parasitoid upon emergence. This stage of a parasitoid''s life has been shown to influence adult responses to volatiles^18–20 and attack rate.⁴ Subsequent location of this same substance whilst foraging could prompt parasitoids to spend an increased time residing in these patches. It has been shown in the hymenopterous whitefly parasitoid Encarsia formosa (Gahan) that honeydew of a range of species including non-hosts will have an arrestant effect, but that host honeydew results in longer searching times.¹⁵ This same effect could account for our findings, and the lower total number of mummies produced could be explained by the innately lower attack rate on M. persicae compared to L. erysimi.In conclusion we draw attention to the following points.

1. It is evident that for some parasitoid species emergence from their mummy case provides information that can manifest itself in long lived host foraging decisions. We hypothesise that aphid honeydew provides an important contact cue that may influence the residence time of D. rapae, and could for other specialist parasitoids.
2. Elucidation of parasitoid host foraging mechanisms provides important information, but increasing experimental complexity may not reveal intuitive results. This is likely to become even more important under heterogeneous field conditions, highlighting the need for corroborating the significance of laboratory studies through well designed field or field-simulation studies.

     

Glucosinolate genetics and the attraction of the aphid parasitoid Diaeretiella rapae to Brassica

The control of insect pests using parasitoids and carnivores has been successfully applied in protected cropping systems, orchards and forestry. Their success in annual field crops has been more limited due largely to the difficulties of attracting and maintaining a sufficient density of parasitoids in the crop before the levls of the insect herbivores become economically damaging. Parasitoids are known to be attracted to host-plant volatiles; thus, manipulating the host-plant chemistry may provide a means of enhancing the attraction of parasitoids to their prey. In this study we describe the differential attraction of the braconid wasp Diaeretiella rapae to two near-isogenic lines of Brassica oleracea which differ in a gene which alters the chemical structure of the isothiocyanates which are emitted following tissue damage. We demonstrate that, by enhancing the production of but-3-enyl isothiocyanate in B. oleracea and Brassica napus (oilseed rape), we can increase the attraction of D. rapae to these plants under standard field conditions.     

Parasitism rate of Myzus persicae (Sulzer) by Diaeretiella rapae (McIntosh) in the presence of an alternative,resistant host

The aphids Lipaphis pseudobrassicae (Davis) and Myzus persicae (Sulzer) (Hemiptera: Aphididae) are important Brassicaceae pests, occurring worldwide and causing significant damage to crops. Interspecific variations in the resistance to natural enemies can potentially impact the interaction among aphid populations. Here we evaluated the hypothesis of associational resistance by determining if the presence of resistant aphids (L. pseudobrassicae) reduces the rate of parasitism by Diaeretiella rapae (McIntosh) on non-resistant aphids (M. persicae). The experiment was conducted using collard green plants infested with M. persicae and L. pseudobrassicae either resistant or susceptible to D. rapae. The percentage of parasitism by D. rapae was greater on L. pseudobrassicae in the susceptible than in the resistant treatment, but parasitism rates on M. persicae did not differ between the treatments. There was no difference in average growth rate between M. persicae and susceptible L. pseudobrassicae populations, but resistant L. pseudobrassicae had greater growth rate than M. persicae. These results suggest that over a short period of time the presence of resistant L. pseudobrassicae does not affect the rate of parasitism by D. rapae on M. persicae.     

Quality of different aphids species as hosts for the parasitoid Aphidius ervi Haliday (Hymenoptera: Braconidae: Aphidiinae)

The suitability of Macrosiphum euphorbiae (Thomas), Aulacorthum solani (Kaltenbach) and Acyrthosiphon kondoi Shinji (Hemiptera: Aphididae) as hosts for the aphid parasitoid Aphidius ervi Haliday was evaluated by assessing host size, host preference, and host quality. Tests were carried out in an environmental chamber at 22±1oC, 70±10% RH and 12h photophase. Replicates (11) consisted of one 24h-old mated female of A. ervi without a previous oviposition experience. Female was released into a Petri dish (5 cm) with 20 2nd and 3rd instars of one of each aphid species tested on a leaf disc of the host plant onto a 1% water-agar layer. Parasitoid emergency was lower in A. kondoi (78.7%) compared to M. euphorbiae (92.2%) and A. solani (91.7%). Acyrthosiphon kondoi (0.36 mm) was the smallest host. The parasitoid showed preference (74.0% parasitism) for M. euphorbiae, the largest host (hind tibia length=0.73 mm), which in turn yielded larger A. ervi females (0.75 mm).     

Brood-size and sex-ratio variation in field populations of three species of solitary aphid parasitoids (Hymenoptera: Braconidae, Aphidiinae)

Solitary parasitoids of colony-forming hosts may produce quasi-gregarious broods, which favours sibmating on the natal patch and local mate competition (LMC). We examined seasonal variations in brood size and sex ratio in three species of solitary parasitoids of aphids associated with trophobiotic ants. Adialytus arvicola, a parasitoid of Sipha agropyrella on grasses, had the smallest broods (mean=4.2, maximum 19), while Lysiphlebus hirticornis, a parasitoid of Metopeurum fuscoviride on tansy, had the largest broods (mean=32.0, maximum 265). In Pauesia pini, a parasitoid of Cinara piceicola on Norway spruce, broods comprised an average of 5.8 (maximum 41) individuals; brood size increased during early summer when hosts became more available but remained the same later in the season. In all three species the sex ratio at eclosion was female-biased, with broods containing approximately two daughters for each son in both A. arvicola and L. hirticornis; the degree of female-bias was least in P. pini. The sex ratio did not vary with brood size. In A. arvicola, the variance of the number of sons declined with an increase in brood size, consistent with "precise" sex allocation. In contrast, in L. hirticornis, the overall sex-ratio variance was greater than its binomial expectation, while it did not differ from binomial in P. pini. A large proportion of broods contained only sons or only daughters, especially in A. arvicola. An excess of male-only broods is expected if constrained females (which can produce only sons) contribute offspring prior to mating. The number of male-only broods, however, did not differ from the number expected if all females are mated and allocate offspring sexes binomially, except in P. pini. In the latter species, broods with two daughters (as opposed to two sons) exceeded binomial expectations. We propose that P. pini is largely outbreeding, while the strongly female-biased sex ratio in A. arvicola and L. hirticornis is consistent with partial sibmating and LMC. Ant-parasitoid interactions could account for a different population mating structure in the three parasitoid species. Both A. arvicola and L. hirticornis mimic the epicuticular hydrocarbon pattern of their aphid hosts. Eclosing wasps are ignored by honeydew-collecting ants and hence can mate and forage on the natal patch. In contrast, P. pini generally depart the mummy area to avoid attacks by trophobiotic ants and mate off patch.     

断脉茧蜂属一新种(膜翅目:茧蜂科)

本报道了采自云南的断脉茧蜂属Heterospilus Haliday一新种：短颊断脉茧蜂Heterospilus breviatus Shi,Yang et Chen,sp nov.,模式标本保存于福建农林大学益虫研究室。     

齿背茧蜂属一新种(膜翅目:茧蜂科)(英文)

本文报道了采自云南的齿背茧蜂属 Acanthormius Ashmead一新种 :双色齿背茧蜂 A.bicolor sp.nov.。模式标本保存于福建农业大学益虫研究室     

中国绒茧蜂属Apanteles Foerster一新种(膜翅目:茧蜂科)

本文报道采自中国福建的茧蜂科Braconidae小腹茧蜂亚科Microgastrinae绒茧蜂属Apanteles Foerster一新种,即透翅绒茧蜂Apanteles pellucipterus Song et Chen,sp.nov.。模式标本存放于福建农林大学植保学院益虫室。     

The role of experience in plant foraging by the aphid parasitoidDiaeretiella rapae (Hymenoptera: Aphidiidae)

Experiments were conducted to test the hypothesis that plant learning by a relative plant-specialist parasitoid wasp should influence the probability of orienting to plant odors (plant finding) and the duration of searching on a plant after landing (plant examining). The insect tested was Diaeretiella rapaeM'Intosh (Hymenoptera: Aphidiidae), a parasitoid wasp that usually attacks aphids on cruciferous plants, but occasionally on other plants. Laboratory experiments using collard as the cruciferous plant and potato as the novel plant demonstrated that postemergence (adult) plant experience affected plant examining only on the less preferred plant, potato, and was reversible and relatively long-term (that is, lasted >2 days). Postemergence experience with potato did not increase orientation to potato odor in a wind tunnel, but postemergence experience with collard resulted in a trend of increased likelihood of flying to collard odor. Preemergence treatments affected plant finding but not plant examining.     

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.