Choice versus no-choice test interpretation and the role of biology and behavior in parasitoid host specificity tests

The need to improve methods and interpretation of host specificity tests for arthropod natural enemies has been clearly identified, yet there remains a paucity of empirical evidence upon which to base recommendations. Factors influencing test outcomes and the mechanisms underlying them must be understood so they can be controlled, and test results can be interpreted correctly. In this study, an established exotic host/parasitoid system was used to assess the outcomes and predictive accuracy of no-choice compared to paired choice tests within small laboratory arenas. Host acceptance by two egg parasitoids, Enoggera nassaui and Neopolycystus insectifurax (Pteromalidae), was interpreted in light of percent parasitism, offspring sex ratios and observed parasitoid behavior. No-choice tests showed that the four host species, Paropsis charybdis, Dicranosterna semipunctata, Trachymela catenata and Trachymela sloanei (Coleoptera: Chrysomelidae) were within the physiological host ranges of both parasitoids. The results of paired choice tests with the first three species supported this interpretation, with two exceptions. Trachymela catenata eggs were not accepted by E. nassaui and were accepted significantly less often by N. insectifurax when compared to no-choice tests. Both test designs predicted that D. semipunctata is within the ecological host range of the two parasitoid species, whereas field evidence suggests this is a false positive result. Percent parasitism of all hosts was higher in no-choice compared to choice tests and was predictive of rank order of host preference in choice tests. Presence of the most preferred host did not increase attack on lower ranked hosts. Offspring sex ratios of E. nassaui were independent of host preference. In contrast, N. insectifurax allocated more females to P. charybdis and mostly males to D. semipunctata and T. catenata. The results support our assertion that both no-choice and choice tests along with detailed behavioral studies should be conducted for correct interpretation of pre-release host specificity tests. This will enable more accurate predictions of parasitoid host ranges and risks parasitoids may pose to non-target organisms in the field.     

Survey of the parasitoids of the tuliptree aphid,Illinoia liriodendri (Hom: Aphididae), in northern California

A survey of the parasitoids ofIllinoia liriodendri (Monell) in northern California conducted from 1988–1990 revealed the presence of 12 primary and 14 hyper-parasitoid species. The most common primary parasitoid wasAphidius polygonaphis (Fitch), which was imported from the eastern United States in the 1970's and is now established throughout the area. New host records were noted forA. ervi Haliday,A. avenaphis (Fitch), Praon occidentale Baker,P. unicum Smith,Diaeretiella rapae M'Intosh,Lysiphlebus testaceipes (Cresson), andMonoctonus nervosus (Haliday) (all Hymenoptera: Braconidae: Aphidiinae), andAphelinus sp. nr.asychis Walker (Hymenoptera: Aphelinidae). The most common hyperparasitoid species werePachyneuron aphidis (Bouché) andAsaphes californicus Girault (both Hymenoptera: Pteromalidae). New hyperparasitoid host records were noted forPachyneuron californicum Girault on Aphidiine and Aphelinidae spp. andCoruna clavata Walker (Hymenoptera: Pteromalidae) onAphelinus sp.     

Non-target parasitism of the endemic New Zealand red admiral butterfly (Bassaris gonerilla) by the introduced biological control agent Pteromalus puparum

The New Zealand red admiral butterfly, Bassaris gonerilla (F.) (Lepidoptera: Nymphalidae), has been known as a non-target host for the introduced biological control agent Pteromalus puparum (L.) (Hymenoptera: Pteromalidae) for at least 35 years, but the level of parasitism has never been quantified. Pre-imaginal mortality in B. gonerilla was assessed over the southern summer of 2000/01 at six field sites in the Christchurch area of the South Island, New Zealand. Individual eggs and larvae were identified by tagging the stem of the Urtica ferox Forst.f. plant on which they were found and the fate of these individuals was checked weekly. These data were used to construct a partial life table for B. gonerilla. Egg mortality was very high (95%), with parasitism by an unidentified Telenomus sp. Haliday (Hymenoptera: Scelionidae) causing 57% mortality. Mortality in the larval and pupal stages increased at a constant rate with age and the major mortality factor was disappearance, which was assumed to be a result of predation and dispersal of larvae. The introduced biological control agent P. puparum parasitized 14% of B. gonerilla pupae sampled. However, parasitism by another exotic parasitoid, the self-introduced Echthromorpha intricatoria (F.) (Hymenoptera: Ichneumonidae), was even higher at 26%. A survey of pupal parasitism in three regions of New Zealand (Wellington, Christchurch, and Dunedin) revealed overall parasitism levels of 67% by E. intricatoria and 8% by P. puparum, but due to the difference in emergence times of B. gonerilla and its parasitoids, these are likely to be overestimates of percent parasitism. It is concluded that P. puparum has permanently enhanced mortality in B. gonerilla, but the level of mortality is low relative to egg parasitism by Telenomus sp., larval disappearance mortality, and pupal mortality due to E. intricatoria parasitism. To determine if this level of pupal parasitism has had population effects will require more data and the development of a population model for B. gonerilla.     

Assessing the non-target impacts of classical biological control agents: is host-testing always necessary?

Release of a biocontrol agent in New Zealand is typically preceded by non-target testing of native or valued species. Nevertheless, if both the target pest and the natural enemy are very different from any native fauna, then there may be no scientific justification for host testing. Gonatocerus ashmeadi (Girault) (Hymenoptera: Mymaridae) is being considered as a biocontrol agent for glassy winged sharpshooter, Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), should the pest arrive. An assessment of the potential impact of G. ashmeadi on New Zealand’s Cicadellidae and Membracidae, from published literature data, indicates that none of these insects is at risk, as their eggs will not be recognised by the parasitoid because either their size or location places them outside the parasitoid’s search pattern. Consequently, there is no scientific case for any non-target host-testing to be carried out in containment.     

Laboratory rearing of the predatory coccinellidCleobora mellyi [Col.: Coccinellidae] for biological control ofParopsis charybdis [Col.: Chrysomelidae] in New Zealand

Cleobora mellyi Mulstant has been introduced into New Zealand in an attempt to controlParopsis charybdis Stål. Artificial diets and a practical method for rearing the predatory Australian ladybird,C. mellyi, are described.     

Redescription of Closterocerus cruy (Girault) (Hymenoptera: Eulophidae: Entedoninae), with new geographical and host records

Abstract  Closterocerus cruy (Girault) is newly recorded, both from New Zealand and as a parasitoid of lepidopteran leafminers. The species is redescribed from the Girault type and from New Zealand material. Diagnostic character states are provided for the separation of C. cruy from the closely related Australian agromyzid parasitoid C. mirabilis Edwards and LaSalle.     

A prospective model for the phenology of Microctonus hyperodae (Hymenoptera: Braconidae), a potential biological control agent of argentine stem weevil in New Zealand

A predictive phenological model is described for the parasitoid Microctonus hyperodae, introduced to New Zealand as a potential biological control agent against Argentine stem weevil Listronotus bonariensis. The model is based on development/temperature relationships obtained from experiments on the parasitoid in quarantine prior to its release, allowing early predictions of its phenology in different parts of the target pest's New Zealand range. In particular the model was used to predict the number of parasitoid generations each year, the degree of temporal synchrony between parasitoid adults and the susceptible adult pest stage, the order of parasitism and reproduction in the pest's life cycle as a possible basis for a simplified, discrete host/parasitoid population model, and the likely significance of ecotypic differences in development and diapause characteristics of the parasitoid. These applications demonstrate the potential for simple models to help in climate matching of classical biological control agents and estimation of their interaction with pest dynamics, using data obtainable prior to their introduction and release. In addition the model proved useful as a decision aid during the release programme, by indicating the likely effects of unusual weather and the need or otherwise for further parasitoid releases.     

Two new species of Chrysomelobia Regenfuss, 1968 (Acariformes: Podapolipidae) from Paropsis charybdis Stål (Coleoptera: Chrysomelidae)

Two new species of Chrysomelobia Regenfuss, 1968, C. alleni n. sp. and C. intrusus n. sp., are described from Tasmanian specimens of the eucalyptus leaf beetle Paropsis charybdis Stål. This beetle is now known to host three species of Chrysomelobia, the other being Chrysomelobia pagurus Seeman, 2008, which is recorded from Tasmania for the first time. Thus, the three species of Paropsis Olivier known to have podapolipid mites each have three mite species from three separate lineages of Chrysomelobia. Collections of P. charybdis in New Zealand (n = 150), where it is an invasive pest species, failed to locate any infested beetles, suggesting that these populations were established by uninfested beetles. The prospect of using these mites as biocontrol agents is discussed.     

Hyperparasitoids of the gum leaf skeletoniser, Uraba lugens Walker (Lepidoptera: Nolidae), with implications for the selection of a biological control agent for Uraba lugens in New Zealand

Abstract  The hyperparasitoids reared from three species of primary parasitoids of the gum leaf skeletoniser, Uraba lugens Walker (Lepidoptera: Nolidae) collected in South Australia and Tasmania are recorded and discussed. Seven hyperparasitoids were reared. Diatora sp. and ? Paraphylax sp. (Ichneumonidae: Cryptinae); Tetrastichus sp. (Chalcidoidea: Eulophidae); Megadicylus dubius (Girault) (Chalcidoidea: Pteromalidae) and Elasmus sp. (Chalcidoidea: Eulophidae) were reared from Cotesia urabae Austin and Allen (Braconidae: Microgastrinae). Megadicylus dubius , Elasmus sp. and Anastatus sp. (Chalcidoidea: Eupelmidae) were reared from Dolichogenidea eucalypti Austin and Allen (Braconidae: Microgastrinae). Pediobius bruchicida (Rondani) (Chalcidoidea: Eulophidae) was reared from Euplectrus sp. (Chalcidoidea: Eulophidae). This appears to be the first record of the cryptine ichneumonid genus Diatora Förster from Australia. Of the seven hyperparasitoid species reared, only one ( P. bruchicida ) is known to be present in New Zealand. Implications for the selection of a biological control agent for U. lugens in New Zealand are discussed. Some prior misidentifications of associated hyperparasitoids are noted.     

Effects of floral resources on the efficacy of a primary parasitoid and a facultative hyperparasitoid

Resources added to agroecosystems to enhance biological control are potentially available to multiple members of the resident insect community—not only the biological control agents for which the resources are intended. Many studies have examined the effects of sugar feeding on the efficacy of biological control agents. However, such information is lacking for other, interacting species such as facultative hyperparasitoids, which may contribute to pest suppression but can also interfere with introduced biological control agents. Under greenhouse conditions, we tested the direct effects of sugar and nectar provisioning on the longevity, host‐killing impact and offspring production of two pupal parasitoids associated with leek moth, Acrolepiopsis assectella: the introduced biological control agent, Diadromus pulchellus, and the native facultative hyperparasitoid, Conura albifrons. Adding sucrose, buckwheat or a combination of buckwheat and common vetch to a sugar‐deprived system (potted leek plants in cages) increased parasitoid longevity and resulted in higher leek moth parasitism and mortality compared to water or common vetch treatments. However, the two parasitoid species exhibited a distinct temporal response to the treatments, likely influenced by differences in their life histories. This study provides insight into how integrating conservation biological control techniques could affect the success of a classical biological control programme.     

Can natural enemies of current insect pests provide biotic resistance to future pests?

1. Economic pests jeopardize agricultural production worldwide. Classical biological control, comprising the import of exotic natural enemies to control target pest populations, has a successful history in many countries. However, little is known about how these natural enemies contribute to the suppression of pests that are yet to arrive. Biotic resistance theory, though, posits that communities resist species invasions as a result of natural enemies.
2. We assessed the potential of the resident exotic parasitoid wasp fauna in New Zealand (intentionally‐introduced biological control agents and unintentionally‐introduced species) to provide biotic resistance against possible future pests. A dataset was generated containing resident exotic parasitoid species (Ichneumonoidea: Braconidae; Ichneumonidae) in New Zealand, as well as their known global host ranges and the pest status of host species, to infer the potential for biotic resistance.
3. The known exotic ichneumonoid fauna in New Zealand comprises 65 species. These species associate with 107 host species in New Zealand, of which 54 species are pests. However, the current exotic species could potentially suppress 442 pest species not yet occurring in New Zealand.
4. This approach could be used to inform pest management programmes worldwide. Future research should consider how biotic resistance from the established parasitoid fauna can be used to inform specific decisions with respect to classical biological control.

     

Field cage evaluation of interspecific interaction of two aphelinid parasitoids and biocontrol effect on Bemisia tabaci (Hemiptera: Aleyrodidae) Middle East‐Asia Minor 1

To explore sustainably effective biological control measures to suppress the super pest Bemisia tabaci (Gennadius) Middle East‐Asia Minor 1 and better understand the biological control effects of single and multiple releases of parasitoids, we evaluated the performance and interaction of two aphelinid parasitoids of B. tabaci, Eretmocerus hayati Zolnerowich & Rose (an exotic primary parasitoid) and Encarsia sophia (Girault & Dodd) (an autoparasitoid, which is controversial in a biological control program). Single species or two species were jointly (1:1 density ratio) released in field cages on cotton in Hebei province, China, in 2010. Results of the field cage experiment showed that all parasitoid release treatments were successful in reducing the densities of the host B. tabaci relative to the control in which no parasitoid was released. The combined release of two parasitoid species showed the highest control effect among the treatments. Different population growth trajectories indicated asymmetric competitive effects of En. sophia on Er. hayati. The densities of Er. hayati were significantly higher in the Er. hayati alone treatment than in the combined release treatment, while densities of En. sophia were lower in the En. sophia alone treatment than in the combined release treatment. Our results demonstrated interspecific competition between autoparasitoid En. sophia and exotic primary parasitoid Er. hayati. However, no evidence indicated that autoparasitoid En. sophia disrupted the host suppression achieved by primary parasitoid Er. hayati. The release of the autoparasitoid together with the primary parasitoid may not influence host suppression in biological control.     

Invasion and Displacement of Experimental Populations of a Conventional Parasitoid by a Heteronomous Hyperparasitoid

Aphelinid parasitoids have an outstanding record of success in programmes of classical biocontrol against whiteflies and scale insects. Heteronomous hyperparasitoids are aphelinids in which the sexes develop on or in different hosts. The female always develops as a primary endoparasitoid of Homoptera. The male develops as a secondary parasitoid hyperparasitoid of his own or another species of homopteran endoparasitoid. Caged experiments were performed with the cabbage whitefly, Aleyrodes proletella, to examine the invasion of a population of a conventional parasitoid, Encarsia inaron both sexes primary endoparasitoids by a heteronomous hyperparasitoid, E. tricolor. In all cages the heteronomous hyperparasitoid successfully invaded an established population of the conventional parasitoid and the conventional species population declined to very low levels within 8 weeks of the introduction of the heteronomous hyperparasitoid. The patterns of invasion were different in each cage. In two cages, high levels of male production by E. tricolor were observed, indicating that hyperparasitism of the conventional species was probably an important factor in causing the decline in the E. inaron population. In a reciprocal experiment in which E. inaron was introduced to an established population of E. tricolor the conventional species failed to invade or persist. A survey of published references to complexes of parasitoids containing a heteronomous hyperparasitoid and one or more conventional species indicated that, in the majority of cases, the heteronomous hyperparasitoid was the most important species in the complex. There are clear implications for the use of these parasitoids in programmes of classical biocontrol. This is because high competitive ability against other parasitoids is not necessarily a good indicator of the ability of a species to maintain high levels of pest control, especially when hyperparasitic behaviour is involved.     

Parasitoids of obscure mealybug,Pseudococcus viburni (Hem.: Pseudococcidae) in California: establishment of Pseudaphycus flavidulus (Hym.: Encyrtidae) and discussion of related parasitoid species

To improve natural suppression of the obscure mealybug, Pseudococcus viburni (Signoret), the parasitoids Pseudaphycus flavidulus (Brèthes) and Leptomastix epona (Walker) (Hymenoptera: Encyrtidae) of Chilean origin were released in California's Central Coast vineyards from 1997 to 1999. A survey for parasitoids of P. viburni was conducted in the Edna Valley appellation wine grape region from 2005 to 2007, 6–8 years after classical biological control releases were discontinued. Two survey methods were used. First, field collections of obscure mealybugs from commercial vineyard blocks (2005–2007) and, second, placement of “sentinel mealybugs” on potted (1 L) grape vines (2006 only). From both survey methods, P. flavidulus was recovered, albeit levels of parasitism were low (less than 0.6%). We also placed longtailed mealybug, Pseudococcus longispinus (Targioni Tozzetti), on potted plants concurrent with placement of sentinel obscure mealybugs in the vineyard in order to measure parasitoid activity on this closely-related mealybug species. No P. flavidulus were recovered from P. longispinus. Other encyrtid parasitoids reared from either P. viburni or P. longispinus were Anagyrus pseudococci (Girault), Leptomastix dactylopii Howard, Leptomastidea abnormis (Girault), Coccidoxenoides perminutus Girault, and Tetracnemoidea peregrina (Compere). A hyperparasitoid, Chaetocerus sp., was also reared. The data are discussed with respect to biological control of vineyard mealybugs and newly developed controls for the Argentine ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae). Because Pseudaphycus species reared from mealybugs are superficially very similar a taxonomic key and discussion of host relationships for selected Pseudaphycus species are provided.     

Phenology and parasitism of the red admiral butterfly

Population densities of the endemic red admiral butterfly, Bassaris gonerilla, were monitored over two summers on Banks Peninsula, New Zealand. Egg-laying usually begins in September and ends in late May. Peaks in egg, larval and adult densities suggest that B. gonerilla completes two full generations per season and in favourable years, a third generation is started but not completed. Population density was lower in a low-rainfall season probably because of the lower survival and nutritional quality of the host plant, Urtica ferox. “Non-target” parasitism levels by Pteromalus puparum (introduced to manage populations of the small white butterfly Pieris rapae) were low at 3.5–16.9% of pupae collected from the field. However, parasitism by the self-introduced pupal parasitoid Echthromorpha intricatoria was very high at 67.5–82.3%. Echthromorpha intricatoria can overwinter in B. gonerilla pupae and is thus capable of attacking all generations of B. gonerilla. More long-term data are needed to determine the status of, and regulatory mechanisms affecting B. gonerilla populations.     

Observations of parasitoid behaviour in both no‐choice and choice tests are consistent with proposed ecological host range

The solitary larval endoparasitoid Eadya daenerys Ridenbaugh (Hymenoptera: Braconidae) is a proposed biocontrol agent of Paropsis charybdis Stål (Coleoptera: Chrysomelidae, Chrysomelinae), a pest of eucalypts in New Zealand. Eadya daenerys oviposition behaviour was examined in two assay types during host range testing, with the aim of improving ecological host range prediction. No‐choice sequential and two‐choice behavioural observations were undertaken against nine closely related species of New Zealand non‐target beetle larvae, including a native beetle, introduced weed biocontrol agents, and invasive paropsine beetles. No behavioural measure was significantly different between no‐choice and two‐choice tests. In sequential no‐choice assays the order of first presentation (target–non‐target) had no significant effect on the median number of attacks or the attack rate while on the plant. Beetle species was the most important factor. Parasitoids expressed significantly lower on‐plant attack rates against non‐targets compared to target P. charybdis larvae. The median number of attacks was always higher towards target larvae than towards non‐target larvae, except for the phylogenetically closest related non‐target Trachymela sloanei (Blackburn) (Coleoptera: Chrysomelidae, Chrysomelinae). Most non‐target larvae were disregarded upon contact, which suggests that the infrequent attack behaviour observed by two individual E. daenerys against Allocharis nr. tarsalis larvae in two‐choice tests and the frass of Chrysolina abchasica (Weise) was probably abnormal host selection behaviour. Results indicate that E. daenerys is unlikely to attack non‐target species apart from Eucalyptus‐feeding invasive paropsines (Chrysomelinae). Non‐lethal negative impacts upon less preferred non‐target larvae are possible if E. daenerys does attack them in the field; however, this is likely to be rare.     

Development of a solitary koinobiont hyperparasitoid in different instars of its primary and secondary hosts

Parasitoid wasps are excellent organisms for studying the allocation of host resources to different fitness functions such as adult body mass and development time. Koinobiont parasitoids attack hosts that continue feeding and growing during parasitism, whereas idiobiont parasitoids attack non-growing host stages or paralyzed hosts. Many adult female koinobionts attack a broad range of host stages and are therefore faced with a different set of dynamic challenges compared with idiobionts, where host resources are largely static. Thus far studies on solitary koinobionts have been almost exclusively based on primary parasitoids, yet it is known that many of these are in turn attacked by both koinobiont and idiobiont hyperparasitoids. Here we compare parasitism and development of a primary koinobiont hyperparasitoid, Mesochorus gemellus (Hymenoptera: Ichneumonidae) in larvae of the gregarious primary koinobiont parasitoid, Cotesia glomerata (Hymenoptera: Braconidae) developing in the secondary herbivore host, Pieris brassicae (Lepidoptera: Pieridae). As far as we know this is the first study to examine development of a solitary primary hyperparasitoid in different stages of its secondary herbivore host. Pieris brassicae caterpillars were parasitized as L1 by C. glomerata and then these parasitized caterpillars were presented in separate cohorts to M. gemellus as L3, L4 or L5 instar P. brassicae. Different instars of the secondary hosts were used as proxies for different developmental stages of the primary host, C. glomerata. Larvae of C. glomerata in L5 P. brassicae were significantly longer than those in L3 and L4 caterpillars. Irrespective of secondary host instar, every parasitoid cluster was hyperparasitized by M. gemellus but all only produced male progeny. Male development time decreased with host stage attacked, whereas adult male body mass did not, which shows that M. gemellus is able to optimally exploit older host larvae in terms of adult size despite their decreasing mass during the pupal stage. Across a range of cocoon masses, hyperparasitoid adult male body mass was approximately 84% as large as primary parasitoids, revealing that M. gemellus is almost as efficient at exploiting host resources as secondary (pupal) hyperparasitoids.     

If and when successful classical biological control fails

Classical biological control of insects has a long history of success, with high benefit–cost ratios. However, most attempts to introduce a biological control agent have been unsuccessful, largely because the agent does not establish in the new environment. This perspectives paper discusses the possibility that even successful biological control may eventually fail, although records show that this is far from a common event. A documented example of eventual biological control failure is discussed and the prospect for future failures analyzed. Part of this analysis is based on an introduced weevil pest in New Zealand and its successful parasitoid biological control agent. The potential fragility of this host–parasitoid relationship is considered, as well as why it may indeed be starting to show signs of instability; this is particularly from the point of view of New Zealand’s often species-poor agricultural ecosystems.     

Host-feeding of three parasitoid species on Bemisia tabaci biotype B and implications for whitefly biological control

Parasitoids in the genera Encarsia and Eretmocerus (Hymenoptera: Aphelinidae) are important biological control agents of whiteflies through their reproductive as well as host‐feeding activities. The feeding capacities of female parasitoids of three species with different reproductive strategies [Encarsia sophia (Girault & Dodd), Encarsia formosa Gahan, and Eretmocerus melanoscutus Zolnerowich & Rose] on their host, sweetpotato whitefly, Bemisia tabaci (Gennadius) biotype B (Homoptera: Aleyrodidae), were evaluated on cabbage in a single‐instar no‐choice experiment in the laboratory and a mixed‐instar choice experiment in the greenhouse. In both single‐ and mixed‐instar experiments, significant differences in host‐feeding capacities were found among the three parasitoid species. Encarsia sophia exhibited superior capacity of host‐feeding compared to E. formosa and E. melanoscutus. In the single‐instar experiment, parasitoids fed more on younger (smaller) hosts than older (larger) hosts. In the mixed‐instar experiments, all three parasitoid species exhibited a clear preference for feeding on older hosts compared to younger hosts. Total number of whitefly nymphs fed on by E. sophia was approximately three times that of the other two parasitoid species. Whitefly mortality accounted for by host‐feeding by E. sophia was up to 59.7%, and, thus, equivalent to parasitization. The significance of host‐feeding of E. sophia for biological control of B. tabaci is discussed.     

Comparison between two species of Eretmocerus (Hymenoptera: Aphelinidae): Reproductive performance is one explanation for more effective control in the field

After the invasion of Australia by the Bemisia tabaci species Middle East-Asia Minor 1 (MEAM1, commonly known as the B biotype), the native parasitoid Eretmocerus mundus (Australian parthenogenetic form) was found to be an ineffective control agent. Eretmocerus hayati was therefore introduced and has substantially improved the level of control. A laboratory study was under taken to determine whether superior life history traits were one explanation for the better performance of E. hayati. We compared adult longevity, daily fecundity and proportion of female progeny of both mated and unmated females. We also compared the traits across females that were either treated with or without the antibiotic rifampicin, an antibiotic that had already been shown to deplete Wolbachia and enable E. mundus to produce males. We found that E. hayati adults survived longer and produced more progeny than E. mundus. Unmated E. hayati females produced only males. Rifampcin had no effect on any of the traits for E. hayati. In contrast, without rifampicin E. mundus females produced mostly female progeny whereas treated females produced mostly males. Recent studies suggest that E. hayati co-evolved with MEAM1, whereas the E. mundus in Australia co-evolved with the entirely distinct Asia members of the complex. This suggests that the underlying evolutionary relationships within the B. tabaci complex may be an important consideration when selecting agents for biological control.