Effect of insect host age and diet on the fitness of the entomopathogenic nematode-bacteria mutualism

Insect host age and diet were evaluated as potential factors that could affect the fitness of the entomopathogenic nematode-bacterium mutualistic partnership. Two nematode species were considered: Steinernema carpocapsae and Heterorhabditis sonorensis, together with their symbionts Xenorhabdus nematophila and Photorhabdus luminescens, respectively. The tobacco hornworm, Manduca sexta, was used as the insect host. Insect developmental stage was a factor that impacted nematode virulence. Non-wandering 5th instar M. sexta were found to be more susceptible to nematode infection compared to wandering 5th instars. This was more noticeable for S. carpocapsae than for H. sonorensis. The nutritional status of the host also had an effect on the fitness of the two nematode species tested. In general, insects fed with the reduced diet content were less susceptible to nematode parasitism. The least observed mortality (0.5 %) was in those M. sexta larvae exposed to the low H. sonorensis dose. Host diet also had an effect on the production of IJ progeny in the insect cadavers. For both nematode species tested, the highest yield of emerging IJs was observed from those insect hosts fed with the low nutrient diet and exposed to the highest nematode inoculum. However, for both nematode species tested, the nutritional status of the host did not significantly affect time of emergence of IJ progeny or the reassociation with their bacterial symbionts (expressed as cfu/IJ). This is the first study on the effect of insect host physiology on both EPN and their symbiotic bacteria fitness.     

Serological study on the transmission of a granulosis virus of the armyworm,Pseudaletia unipuncta (Lepidoptera: Noctuidae), to other lepidopterous species

The synergistic (Hawaiian) strain of a granulosis virus (GV) from the armyworm, Pseudaletia unipuncta, was transmitted to Spodoptera exigua, Autographa californica, and Trichoplusia ni. The viruses isolated from these hosts were tested by radial double-immunodiffusion (RDD) and immunoelectrophoresis (IE) for their relationship to the original virus. Untreated and heat-treated virus inclusion bodies (capsules) were compared for their antigenic properties but no differences were detected. The antiserum elicited against the whole capsule was more sharply specific for the antigenic determinants than the one elicited against the dissolved capsule proteins. The viruses obtained from S. exigua and T. ni elicited precipitin lines that differed from those of the P. unipuncta GV in their electrophoretic mobility with the one-trough IE method; however, with the two-trough method, the lines fused indicating that the antigens were identical. The major precipitin line indicating identity of the viruses wasthat produced by the synergistic factor (SF) purified from the capsule proteins of the synergistic GV strain. The presence of SF in the GV produced in alternate hosts indicated that its production was virus directed. The SF was not detected in the GVs of Laspeyresia pomonella and Pieris rapae and in the nonsynergistic Oregonian GV of P. unipuncta. A field-collected GV from S. exigua exhibited a different precipitin pattern from that of the synergistic GV, but one of the precipitin lines shared partial relationship to the SF.     

Changes in growth and virulence of a nuclear polyhedrosis virus from Choristoneura fumiferana after passage in Trichoplusia ni and Galleria mellonella

An isolate of nuclear polyhedrosis virus from Choristoneura fumiferana was fed to neonate larvae of Trichopulsia ni and Galleria mellonella. It caused infection and mortality in both of these species. After passage in the alternate hosts, the isolate became increasingly virulent for these hosts. The passaged virus retained its infectivity for Choristoneura but diseased larvae did not wilt and at death they were found to contain only a few polyhedra indicating the virus had been changed.     

Infectivity of a nuclear polyhedrosis virus from the alfalfa looper,Autographa californica,after passage through alternate hosts

A nuclear polyhedrosis virus isolated from the alfalfa looper, Autographa californica, was found to infect several species of caterpillars including the cabbage looper, Trichoplusia ni; the beet armyworm, Spodoptera exigua; and the saltmarsh caterpillar, Estigmene acrea. Studies were therefore conducted to determine the quantitative effects of passage through the alternate hosts, S. exigua and E. acrea, on the infectivity of this virus to newly hatched first-instar cabbage looper larvae. When 11 preparations of polyhedra obtained from a like number of primary passages through the original or alternate hosts were assayed and the mortality at 7-, 10-, and 14-day intervals were subjected to probit analysis, the LD₅₀s for the three intervals differed but those for the preparations at any given interval did not. Therefore, any of the three hosts could be used to propagate the virus, and whichever proves the easiest to rear and provides the highest yields of polyhedra can be selected.     

Do Parasitic Trematode Cercariae Demonstrate a Preference for Susceptible Host Species?

Many parasites are motile and exhibit behavioural preferences for certain host species. Because hosts can vary in their susceptibility to infections, parasites might benefit from preferentially detecting and infecting the most susceptible host, but this mechanistic hypothesis for host-choice has rarely been tested. We evaluated whether cercariae (larval trematode parasites) prefer the most susceptible host species by simultaneously presenting cercariae with four species of tadpole hosts. Cercariae consistently preferred hosts in the following order: Anaxyrus ( = Bufo) terrestris (southern toad), Hyla squirella (squirrel tree frog), Lithobates ( = Rana) sphenocephala (southern leopard frog), and Osteopilus septentrionalis (Cuban tree frog). These host species varied in susceptibility to cercariae in an order similar to their attractiveness with a correlation that approached significance. Host attractiveness to parasites also varied consistently and significantly among individuals within a host species. If heritable, this individual-level host variation would represent the raw material upon which selection could act, which could promote a Red Queen “arms race” between host cues and parasite detection of those cues. If, in general, motile parasites prefer to infect the most susceptible host species, this phenomenon could explain aggregated distributions of parasites among hosts and contribute to parasite transmission rates and the evolution of virulence. Parasite preferences for hosts belie the common assumption of disease models that parasites seek and infect hosts at random.     

Effects of the polydnavirus of Cotesia congregata on the immune system and development of non-habitual hosts of the parasitoid

Polydnaviruses (PDV) are obligate mutualistic symbionts found in association with some groups of parasitic Hymenoptera. In these groups, they suppress the immune response of the parasitoid’s host and are required for successful parasitoid reproduction. Several PDV effects have been described in different experimental systems, but no clear picture of PDV mode of immunosuppression has emerged. No study to date has directly tested if PDV modes of action are evolutionarily conserved or divergent among parasitoid taxa within the Ichneumonoidea. We hypothesize the divergence in PDV mode of immunosuppression can be detected by identifying points of divergence in the immune response of different host species to PDV from one parasitoid species. This study tests the effects of purified PDV from Cotesia congregata on the immune response of three larval lepidopteran species that naturally are hosts of parasitoid species that differ in taxonomic relatedness to C. congregata. Here we demonstrate that despite associations with distantly related parasitoids (Ichneumonidae and Braconidae), Manduca sexta and Heliothis virescens showed similar patterns of increased glucose dehydrogenase (GLD) activity, suppressed cellular encapsulation in vitro, and increased time to pupation. In contrast, Lymantria dispar showed no response to C. congregata PDV across any of the parameters measured, even though it has an evolutionary association with several parasitoids closely related to C. congregata and within the Microgastrinae. The PDV immunosuppression in H. virescens and M. sexta does not correlate with host molecular phylogeny either. The suborganismal effects shown in M. sexta and H. virescens translated into significantly reduced pupation success in M. sexta only. Results demonstrate that while some PDV modes of immunosuppression in hosts may be divergent, others may be conserved across broad host groups.     

Postemergence Experience Affects Sex Ratio Allocation in a Gregarious Insect Parasitoid

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

Lack of Host Specialization on Winter Annual Grasses in the Fungal Seed Bank Pathogen Pyrenophora semeniperda

Generalist plant pathogens may have wide host ranges, but many exhibit varying degrees of host specialization, with multiple pathogen races that have narrower host ranges. These races are often genetically distinct, with each race causing highest disease incidence on its host of origin. We examined host specialization in the seed pathogen Pyrenophora semeniperda by reciprocally inoculating pathogen strains from Bromus tectorum and from four other winter annual grass weeds (Bromus diandrus, Bromus rubens, Bromus arvensis and Taeniatherum caput-medusae) onto dormant seeds of B. tectorum and each alternate host. We found that host species varied in resistance and pathogen strains varied in aggressiveness, but there was no evidence for host specialization. Most variation in aggressiveness was among strains within populations and was expressed similarly on both hosts, resulting in a positive correlation between strain-level disease incidence on B. tectorum and on the alternate host. In spite of this lack of host specialization, we detected weak but significant population genetic structure as a function of host species using two neutral marker systems that yielded similar results. This genetic structure is most likely due to founder effects, as the pathogen is known to be dispersed with host seeds. All host species were highly susceptible to their own pathogen races. Tolerance to infection (i.e., the ability to germinate even when infected and thereby avoid seed mortality) increased as a function of seed germination rate, which in turn increased as dormancy was lost. Pyrenophora semeniperda apparently does not require host specialization to fully exploit these winter annual grass species, which share many life history features that make them ideal hosts for this pathogen.     

A field test of the dilution effect hypothesis in four avian multi-host pathogens

The Dilution Effect Hypothesis (DEH) argues that greater biodiversity lowers the risk of disease and reduces the rates of pathogen transmission since more diverse communities harbour fewer competent hosts for any given pathogen, thereby reducing host exposure to the pathogen. DEH is expected to operate most intensely in vector-borne pathogens and when species-rich communities are not associated with increased host density. Overall, dilution will occur if greater species diversity leads to a lower contact rate between infected vectors and susceptible hosts, and between infected hosts and susceptible vectors. Field-based tests simultaneously analysing the prevalence of several multi-host pathogens in relation to host and vector diversity are required to validate DEH. We tested the relationship between the prevalence in house sparrows (Passer domesticus) of four vector-borne pathogens–three avian haemosporidians (including the avian malaria parasite Plasmodium and the malaria-like parasites Haemoproteus and Leucocytozoon) and West Nile virus (WNV)–and vertebrate diversity. Birds were sampled at 45 localities in SW Spain for which extensive data on vector (mosquitoes) and vertebrate communities exist. Vertebrate censuses were conducted to quantify avian and mammal density, species richness and evenness. Contrary to the predictions of DEH, WNV seroprevalence and haemosporidian prevalence were not negatively associated with either vertebrate species richness or evenness. Indeed, the opposite pattern was found, with positive relationships between avian species richness and WNV seroprevalence, and Leucocytozoon prevalence being detected. When vector (mosquito) richness and evenness were incorporated into the models, all the previous associations between WNV prevalence and the vertebrate community variables remained unchanged. No significant association was found for Plasmodium prevalence and vertebrate community variables in any of the models tested. Despite the studied system having several characteristics that should favour the dilution effect (i.e., vector-borne pathogens, an area where vector and host densities are unrelated, and where host richness is not associated with an increase in host density), none of the relationships between host species diversity and species richness, and pathogen prevalence supported DEH and, in fact, amplification was found for three of the four pathogens tested. Consequently, the range of pathogens and communities studied needs to be broadened if we are to understand the ecological factors that favour dilution and how often these conditions occur in nature.     

Electroantennogram (EAG) responses of Microplitis croceipes and Cotesia marginiventris and their lepidopteran hosts to a wide array of odor stimuli: Correlation between EAG response and degree of host specificity?

In order to test whether the electroantennogram (EAG) response spectrum of an insect correlates to its degree of host specificity, we recorded EAG responses of two parasitoid species with different degrees of host specificity, Microplitis croceipes (specialist) and Cotesia marginiventris (generalist), to a wide array of odor stimuli including compounds representing green leaf volatiles (GLVs), herbivore-induced plant volatiles (HIPV), ecologically irrelevant (not used by the parasitoid species and their hosts for host location) plant volatiles, and host-specific odor stimuli (host sex pheromones, and extracts of host caterpillar body and frass). We also tested the EAG responses of female moths of the caterpillar hosts of the parasitoids, Heliothis virescens and Spodoptera exigua, to some of the odor stimuli. We hypothesized that the specialist parasitoid will have a narrower EAG response spectrum than the generalist, and that the two lepidopteran species, which are similar in their host plant use, will show similar EAG response spectra to plant volatiles. As predicted, the specialist parasitoid showed greater EAG responses than the generalist to host-specific odor and one HIPV (cis-3-hexenyl butyrate), whereas the generalist showed relatively greater EAG responses to the GLVs and unrelated plant volatiles. We detected no differences in the EAG responses of H. virescens and S. exigua to any of the tested odor.     

The infectivity of a nuclear polyhedrosis virus of the velvetbean caterpillar for eight noctuid hosts

Eight species of noctuid larvae were tested for susceptibility to a nuclear polyhedrosis virus of the velvetbean caterpillar, Anticarsia gemmatalis. Velvetbean caterpillar larvae were highly susceptible to crude preparations of polyhedral inclusion bodies (PIBs; LD₅₀ = 4.7 PIBs/larva), but preparations of purified polyhedra were much less effective against these larvae (LD₅₀ = 319.7 PIBs/larva). Of seven other noctuid species tested, only Heliothis virescens was as susceptible to the virus as A. gemmatalis. High dosages were required to kill Heliothis zea, Trichoplusia ni, Pseudoplusia includens, and Spodoptera ornithogalli. Plathypena scabra and Spodoptera frugiperda were not susceptible.     

Interspecific discrimination and larval competition amongMicroplitis croceipes,Microplitis demolitor,Cotesia kazak (Hym.: Braconidae), andHyposoter didymator (Hym.: Ichneumonidae), parasitoids ofHeliothis virescens (Lep.: Noctuidae)

Interspecific host discrimination by adults, and larval competition among the endoparasitoidsMicroplitis croceipes (Cresson),Microplitis demolitor Wilkinson,Cotesia kazak (Telenga) andHyposoter didymator (Thunberg) were investigated usingHeliothis virescens (F.) as the host. In ovipositional choice tests, the mean number of encounters and ovipositions for unparasitized hosts was not significantly different from the mean number of encounters and ovipositions for parasitized hosts for each treatment combination (P>0.05). Thus, none of the parasitoid species discriminated between host larvae recently parasitized once by a female of another species und unparasitized hosts. However, in all but two cases, females did discriminate between unparasitized hosts and hosts in which an early first instar of the first-attacking species was developing.Cotesia kazak andH. didymator did not discriminate between unparasitized hosts and hosts parasitized by an early first instar ofM. demolitor. Larval competition among these parasitoid species was studied for three time intervals between the first and second species parasitization: 1) second species attack immediately (5–15 sec) after the first; 2) second species attack 24 h after the first; and 3) second species attack 48 h after the first. Time until egg eclosion was shortest forM. demolitor, thenC. kazak, thenM. croceipes, and longest forH. didymator. When the second parasitoid species attacked a host immediately after the first species, the species in which egg eclosion occurred first was the victor more frequently, except whenM. demolitor competed withC. kazak andH. didymator. With a 24 h delay between the first and second species to attack, the older first instar from the first parasitization usually outcompeted the younger first instar from the second attack. A first instar from the second species to attack generally outcompeted the second instar of the first species when the second parasitization had been delayed 48 h. Competiors were eliminated mainly by physical attack, butC. kazak andM. croceipes apparently also killedH. didymator eggs by physiological processes.     

A comparison of methodologies for the assessment of host preference of the gregarious egg parasitoid Trichogramma platneri

The innate preference of Trichogramma platneri for the eggs of six host species (Chrysoperla carnea (Stephens), Cydia pomonella (L.), Ephestia kuehniella (Zeller), Helicoverpa zea (Boddie), Manduca sexta (L.), and Sitotroga cerealella (Olivier)) was evaluated as the first host accepted by an individual female parasitoid when eggs were presented simultaneously. Selective exploitation of the same hosts by T. platneri was evaluated in no-choice, paired-choice, and multiple-choice tests, using number of parasitoids emerged, proportion of female offspring, and proportion of time spent on host eggs as different measures of preference. T. platneri showed a strong innate preference for C. pomonella and M. sexta. H. zea and M. sexta were the most preferred hosts and S. cerealella the least preferred, in the no-choice and choice tests. The number of progeny emerged and proportion of female offspring were equally suitable measures of host preference for T. platneri. Although no-choice and choice tests provided very similar preference ranking for T. platneri, a polyphagous species, the no-choice tests appeared poorer at separating hosts that were close in rank and multiple-choice tests were considered likely to be more realistic for more specialized control agents.     

Risk Assessment Studies: Detailed Host Range Testing of Wild-Type Cabbage Moth, Mamestra brassicae (Lepidoptera: Noctuidae), Nuclear Polyhedrosis Virus

The host range of a multiply enveloped nuclear polyhedrosis virus (NPV) (Baculoviridae) isolated from the cabbage moth, Mamestra brassicae (Lepidoptera: Noctuidae), was determined by challenging a wide range of insect species with high (10⁶ polyhedral inclusion bodies) and low (10³ polyhedral inclusion bodies) doses of the virus. The identity of the progeny virus was confirmed by dot blotting. Analysis of 50% lethal dose was carried out on selected species, and the progeny virus was identified by using restriction enzyme analysis and Southern blotting. Other than the Lepidoptera, none of the species tested was susceptible to M. brassicae NPV. Within the Lepidoptera, M. brassicae NPV was infective to members of four families (Noctuidae, Geometridae, Yponomeutidae, and Nymphalidae). Of 66 lepidopterous species tested, M. brassicae NPV was cross-infective to 32 of them; however, 91% of the susceptible species were in the Noctuidae. The relevance of host range data in risk assessment studies is discussed.     

Evaluation of 31 Potential Biofumigant Brassicaceous Plants as Hosts for Three Meloiodogyne Species

Brassicaceous cover crops can be used for biofumigation after soil incorporation of the mowed crop. This strategy can be used to manage root-knot nematodes (Meloidogyne spp.), but the fact that many of these crops are host to root-knot nematodes can result in an undesired nematode population increase during the cultivation of the cover crop. To avoid this, cover crop cultivars that are poor or nonhosts should be selected. In this study, the host status of 31 plants in the family Brassicaceae for the three root-knot nematode species M. incognita, M. javanica, and M. hapla were evaluated, and compared with a susceptible tomato host in repeated greenhouse pot trials. The results showed that M. incognita and M. javanica responded in a similar fashion to the different cover cultivars. Indian mustard (Brassica juncea) and turnip (B. rapa) were generally good hosts, whereas most oil radish cultivars (Raphanus. sativus ssp. oleiferus) were poor hosts. However, some oil radish cultivars were among the best hosts for M. hapla. The arugula (Eruca sativa) cultivar Nemat was a poor host for all three nematode species tested. This study provides important information for chosing a cover crop with the purpose of managing root-knot nematodes.     

Pathology of a nuclear polyhedrosis virus of the alfalfa looper in alternate hosts

The symptomatology and histopathology of a nuclear polyhedrosis virus isolated from a larva of the alfalfa looper, Autographa californica, was studied by examining 13 tissues in the original and following alternate hosts: cabbage looper, Trichoplusia ni; beet armyworm, Spodoptera exigua; saltmarsh caterpillar, Estigmene acrea; corn carworm, Heliothis zea; cotton leafperforator, Bucculatrix thurberiella; and diamondback moth, Plutella xylostella. In all hosts, the hypodermal, tracheal matrix, and fat body cells were infected. Other tissues infected in some hosts included the Malpighian tubules, muscle, hemocytes, ganglia, midgut, hindgut, juvenile tissue (imaginal buds), and testes. No major changes in tissue tropisms were observed. The external symptoms were typical of nuclear polyhedrosis in all species except the corn earworm; in this host, development of the disease and death were delayed.     

Dynamics of Vector-Host Interactions in Avian Communities in Four Eastern Equine Encephalitis Virus Foci in the Northeastern U.S.

Background

Eastern equine encephalitis (EEE) virus (Togaviridae, Alphavirus) is a highly pathogenic mosquito-borne zoonosis that is responsible for occasional outbreaks of severe disease in humans and equines, resulting in high mortality and neurological impairment in most survivors. In the past, human disease outbreaks in the northeastern U.S. have occurred intermittently with no apparent pattern; however, during the last decade we have witnessed recurring annual emergence where EEE virus activity had been historically rare, and expansion into northern New England where the virus had been previously unknown. In the northeastern U.S., EEE virus is maintained in an enzootic cycle involving the ornithophagic mosquito, Culiseta melanura, and wild passerine (perching) birds in freshwater hardwood swamps. However, the identity of key avian species that serve as principal virus reservoir and amplification hosts has not been established. The efficiency with which pathogen transmission occurs within an avian community is largely determined by the relative reservoir competence of each species and by ecological factors that influence contact rates between these avian hosts and mosquito vectors.

Methodology and principle findings

Contacts between vector mosquitoes and potential avian hosts may be directly quantified by analyzing the blood meal contents of field-collected specimens. We used PCR-based molecular methods and direct sequencing of the mitochondrial cytochrome b gene for profiling of blood meals in Cs. melanura, in an effort to quantify its feeding behavior on specific vertebrate hosts, and to infer epidemiologic implications in four historic EEE virus foci in the northeastern U.S. Avian point count surveys were conducted to determine spatiotemporal host community composition. Of 1,127 blood meals successfully identified to species level, >99% of blood meals were from 65 avian hosts in 27 families and 11 orders, and only seven were from mammalian hosts representing three species. We developed an empirically informed mathematical model for EEE virus transmission using Cs. melanura abundance and preferred and non-preferred avian hosts. To our knowledge this is the first mathematical model for EEE virus, a pathogen with many potential hosts, in the northeastern U.S. We measured strong feeding preferences for a number of avian species based on the proportion of mosquito blood meals identified from these bird species in relation to their observed frequencies. These included: American Robin, Tufted Titmouse, Common Grackle, Wood Thrush, Chipping Sparrow, Black-capped Chickadee, Northern Cardinal, and Warbling Vireo. We found that these bird species, most notably Wood Thrush, play a dominant role in supporting EEE virus amplification. It is also noteworthy that the competence of some of the aforementioned avian species for EEE virus has not been established. Our findings indicate that heterogeneity induced by mosquito host preference, is a key mediator of the epizootic transmission of vector-borne pathogens.

Conclusion and significance

Detailed knowledge of the vector-host interactions of mosquito populations in nature is essential for evaluating their vectorial capacity and for assessing the role of individual vertebrates as reservoir hosts involved in the maintenance and amplification of zoonotic agents of human diseases. Our study clarifies the host associations of Cs. melanura in four EEE virus foci in the northeastern U.S., identifies vector host preferences as the most important transmission parameter, and quantifies the contribution of preference-induced contact heterogeneity to enzootic transmission. Our study identifies Wood Thrush, American Robin and a few avian species that may serve as superspreaders of EEE virus. Our study elucidates spatiotemporal host species utilization by Cs. melanura in relation to avian host community. This research provides a basis to better understand the involvement of Cs. melanura and avian hosts in the transmission and ecology of EEE virus and the risk of human infection in virus foci.     

Pathogenicity Tests on Nine Mosquito Species and Several Non-target Organisms with Strelkovimermis spiculatus (Nemata Mermithidae)

Nine species of mosquitoes and several species of non-target aquatic organisms were tested for susceptibility to the mernaithid nematode, Strelkovimermis spiculatus. All species of Anopheles, Aedes, Culex, and Toxorhynchites exposed to S. spiculatus were susceptible. Of the nine mosquito species tested, C. pipiens quinquefasciatus had the greatest tolerance to initial invasion and the highest percent infection of those that survived. High levels of infection were also achieved with Aedes taeniorhynchus and A. albopictus, but these mosquitoes were significantly less tolerant to parasitism than C. pipiens quinquefasciatus. Strelkovimermis spiculatus did not infect or develop in any of the non-target hosts tested.     

Linkages between nectaring and oviposition preferences of Manduca sexta on two co‐blooming Datura species in the Sonoran Desert

1. The oviposition choices of phytophagous insects determine the environment that their offspring will experience, affecting both larval performance and host plant fitness. These choices, however, may be influenced by other activities, such as nectar foraging. 2. In the Sonoran Desert, Manduca sexta (Lepidoptera: Sphingidae) oviposits primarily on the perennial herb Datura wrightii. It has been reported to oviposit on the smaller‐flowered, co‐blooming, sympatric annual Datura discolor as well. Datura is also M. sexta's most important source of nectar in this region. Nectaring and oviposition decisions thus determine M. sexta's reproductive success, as well as the relative benefits (pollination) and costs (herbivory) that each Datura species derives from this interaction. 3. The nectaring and oviposition choices of adult M. sexta on these congeners were studied to investigate how nectar foraging influences oviposition. Larval performance on the two hosts was then assessed. 4. Nectaring and oviposition were behaviourally linked, with M. sexta preferring the perennial D. wrightii as both a nectar source and larval host when given a choice between the two species. This preference disappeared, however, when only D. discolor bore flowers. 5. In the laboratory, larvae developed at equal rates when fed D. wrightii or D. discolor leaves, but survival was higher on D. wrightii when larvae fed on intact plants. 6. These findings suggest that while female preferences match larval performance in most cases, the link between nectaring and oviposition may at times bias moths to lay eggs on inferior larval hosts.