Comparison of categories of resistance in wheat and barley genotypes against biotype 2 of the Russian wheat aphid, Diuraphis noxia (Kurdjumov)

The Russian wheat aphid Diuraphis noxia (Kurdjumov) (Homoptera: Aphididae) is a global pest of wheat and barley. This arthropod is difficult to manage with pesticides or biological control agents due to the aphid’s ability to seek shelter in rolled leaves and also to develop virulent biotypes. During the past 20 years, the use of aphid-resistant cereal cultivars has proven to be an economically and ecologically beneficial method of protecting crops from D. noxia damage. Our research reports the results of experiments to determine the categories of D. noxia biotype 2 resistance present in Cereal Introduction Triticeae (CItr) 2401, and a barley genotype (IBRWAGP4-7), compared to control resistant and susceptible wheat and barley genotypes. CItr2401 and IBRWAGP4-7 exhibit no antixenosis, but both genotypes demonstrated antibiosis to D. noxia in the form of reduced aphid populations. Reduced leaf dry weight change, a measure of plant tolerance of D. noxia feeding, was significantly less in CItr2401 and IBRWAGP4-7 plants than in plants of susceptible control varieties. However, tolerance was negated when a tolerance index was calculated to correct for differences in aphid populations. Barley IBRWAGP4-7 is a new source of D. noxia biotype 2 resistance. D. noxia foliar leaf damage and population growth were significantly less on IBRWAGP4-7 plants than on plants of the susceptible barley variety Morex. IBRWAGP4-7 plants were equal in resistance to plants of the resistant barley STARS 9301 and wheat genotype CItr2401. Handling editor: Heikki Hokkanen     

Interactions of Russian wheat aphid, a hymenopterous parasitoid and resistant and susceptible slender wheatgrasses

Interactions among three trophic levels of resistant and susceptible slenderwheat grasses, Elymus trachycaulum (Link) Goule ex Shinners ex. H.F. Lewis, Russian wheat aphid, Diuraphis noxia (Mordvilko), and a hymenopterous parasitoid were studied in the laboratory and greenhouse. These relationships were compared with a commercial susceptible wheat Triticum aestivum L. variety. Aphids reared on the resistant entries showed significantly lower weights and numbers. Significant reduction of parasitoid mummy weight and adult size was positively correlated with the effects on the aphids. Resistant entries also induced a longer prereproductive period for both the aphids and parasitoids. Numbers of aphids and aphid damage were significantly modified by the addition of parasitoids. Parasitism was higher on plants that did not have leaf rolling. These findings may indicate that antibiosis resistance studied here is not the most desirable because it decreases natural enemy vitality.     

Species diversity, abundance, and phenology of aphid natural enemies on spring wheats resistant and susceptible to Russian wheat aphid

The species composition, relativeabundance, and seasonal dynamics of selectednatural enemies of cereal aphids were monitoredin spring wheat fields in Moscow, Idaho in 1997and 1998. Trials also examined the potentialimpact of resistance to Russian wheat aphid(RWA), Diuraphis noxia (Mordvilko)(Homoptera: Aphididae) in wheat, on aphidbiological control agents. Natural enemypopulations were monitored on two springwheats: D. noxia susceptible variety`Centennial' and resistant genotype `IDO488'. Field plots were artificially infested withadult D. noxia, and sampled for cerealaphids and parasitoids weekly. Coccinellidpredators were monitored once in 1997 and twicein 1998. The coccinellids Hippodamiaconvergens Guerin, Coccinellaseptempunctata L., C. transversoguttataBrown and C. trifasciata Mulsant weredetected. No significant differences in adultor immature coccinellid densities were observedbetween the D. noxia resistant andsusceptible genotypes. During both years, themost abundant primary hymenopteran parasitoidswere Diaeretiella rapae (M'Intosh), Aphidius ervi Haliday, A. avenaphis(Fitch), and Lysiphlebus testaceipes(Cresson), Aphelinus varipes (Foerster),Aphidius colemani Viereck, Aphidiuspicipes (Nees), Aphidius sp., Monoctonus washingtonensis Pike & Stary, Praon gallicum Stary, Praon occidentaleBaker, and Praon sp. were also detected. Numbers of both D. noxia and D.rapae were significantly greater on Centennialthan on IDO488 in both years. When all speciesof cereal aphids and parasitoids areconsidered, the total percentage parasitism wasnot significantly different between thegenotypes. There was no interaction betweenD. noxia resistance and the populationdensity of the predators or parasitoidsmonitored. These results suggest that the D. noxia resistant line had no adverse impacton natural enemies under the conditions ofthese field experiments.     

Release and recovery in South Africa of the exotic aphid parasitoid <Emphasis Type="Italic">Aphelinus hordei</Emphasis> verified by the polymerase chain reaction

The exotic aphid parasitoid Aphelinushordei Kurdjumov (Hymenoptera: Aphelinidae) was released at five Russian wheat aphid [Diuraphis noxia (Mordvilko)] infested wheat fields in the eastern parts of the Free State Province of South Africa during the 1998 and 1999 growing seasons. Except for differences in the setae on the ventralside of the forewings, this species is verysimilar in colour and structure to A.varipes (Foerster) and A. albipodusHayat & Fatima, which also parasitise D.noxia. It is therefore difficult todistinguish between them, and to determinetheir establishment. Therefore a polymerasechain reaction, using specific primers for bothITS2 and mitochondrial 16s DNA sequencesof the three parasitoids, followed by HinfIrestriction endonuclease digestion and agarosegel electrophoresis, was tested to distinguishbetween them. Parasitoid recoveries were madeat the release sites within weeks after theywere released. Putative individuals of A.hordei were also collected during 1999 and2000 on D. noxia in Lesotho, whichis situated on the eastern border of the FreeState Province. The procedure separated the three Aphelinus spp.reliably. Between 94 and 100% of theindividuals recovered during the two fieldseasons were identified as being A.hordei, thus verifying recovery of this exoticaphid parasitoid in South Africa.     

Hymenopteran parasitoids and dipteran predators of the invasive aphid Diuraphis noxia after enemy introductions: Temporal variation and implication for future aphid invasions

Shifts in prevalence and abundance of hymenopteran parasitoids and dipteran predators, Diuraphis noxia, and other aphids were measured in the west-central Great Plains of North America, April–September, in 2001 and 2002, corresponding to over a decade after first detection of D. noxia and first release of D. noxia enemies. Significant temporal shifts in enemy species prevalence and diversity were detected in this study and more broadly during an 11 year time span. At any given time, some species were relatively common. One parasitoid had been predominant throughout (Aphelinus albipodus), two had shifted in dominance (Lysiphlebus testaceipes and Diaeretiella rapae), three parasitoids had been detected infrequently (Aphidius avenaphis, Aphidius matricariae, and Aphelinus asychis), one parasitoid was detected in the 1990s but not during 2001 and 2002 (Aphelinus varipes), two predatory flies occurred at occasional significant levels (Leucopis gaimarii and Eupeodes volucris), and two parasitoids may have been minor members of the fauna (Aphidius ervi and Praon yakimanum). Aphid populations detected were usually very low or not detected, precluding estimation of percent parasitism. The best evidence of suppression was observations of parasitoids in the rare case of D. noxia exceeding economic thresholds, which complemented past studies using high aphid densities. The D. noxia enemies detected were primarily endemic or long-time residents derived from previous introductions. This enemy community may provide flexibility in responding to a future aphid invasion, allowing more strategic use of biological control and other pest management approaches.     

A multi‐genome analysis approach enables tracking of the invasion of a single Russian wheat aphid (Diuraphis noxia) clone throughout the New World

This study investigated the population genetics, demographic history and pathway of invasion of the Russian wheat aphid (RWA) from its native range in Central Asia, the Middle East and Europe to South Africa and the Americas. We screened microsatellite markers, mitochondrial DNA and endosymbiont genes in 504 RWA clones from nineteen populations worldwide. Following pathway analyses of microsatellite and endosymbiont data, we postulate that Turkey and Syria were the most likely sources of invasion to Kenya and South Africa, respectively. Furthermore, we found that one clone transferred between South Africa and the Americas was most likely responsible for the New World invasion. Finally, endosymbiont DNA was found to be a high‐resolution population genetic marker, extremely useful for studies of invasion over a relatively short evolutionary history time frame. This study has provided valuable insights into the factors that may have facilitated the recent global invasion by this damaging pest.     

Abundance and natural control of the woolly aphid <Emphasis Type="Italic">Eriosoma lanigerum</Emphasis> in an Australian apple orchard IPM program

Woolly aphid (Eriosoma lanigerum Hausmann) (Hemiptera: Aphididae), was monitored over three growing seasons (1995--1998) to assess its abundance and management under apple IPM programs at Bathurst on the Central Tablelands of NSW, Australia. Woolly aphid infestations were found to be extremely low in IPM programs utilising mating disruption and fenoxycarb for codling moth Cydia pomonella L. (Lepidoptera: Tortricidae) control. This was the direct result of increased numbers of natural enemies. No insecticides were applied for woolly aphid control. Under the IPM strategies tested the principal control agent was identified as European earwig (Forficula auricularia L.) (Dermaptera: Forficulidae). Earwigs in combination with Aphelinus mali (Haldeman) (Hymenoptera: Aphelinidae) reduced woolly aphid infestations below the action threshold set by commercial growers. However, A. mali together with other flying natural enemies, e.g., ladybirds, lacewings and hoverflies, did not provide commercially acceptable control of woolly aphid in the absence of earwigs. Under the conventional spray program, using the broad-spectrum insecticide azinphos-methyl for codling moth control, the level of woolly aphid infestation increased with each successive season and biological control was not established. When azinphos-methyl was withdrawn, natural enemies migrated in and provided control of woolly aphid within one season. This is the first study to show that the biological control of woolly aphid can be achieved in a commercially viable IPM program.     

Instar-specific defense of the pea aphid,Acyrthosiphon pisum: Influence on oviposition success of the parasiteAphelinus asychis (Hymenoptera: Aphelmidae)

The parasite Aphelinus asychisWalker (Hymenoptera: Aphelinidae) oviposits in all four instars of the pea aphid, Acyrthosiphon pisum(Harris) (Homoptera: Aphididae). Searching females display a highly stereotyped sequence of behaviors when encountering a host. Once recognized, an aphid is examined and probed by the wasp with the everted ovipositor prior to oviposition. Oviposition success is influenced by aphid behavior that is related to aphid size and expressed through instarspecific escape and defense reactions. Being smaller and less able to defend themselves, first and early-second instars of pea aphid are more susceptible to successful parasitism than third and fourth instars, in that order. Observed patterns of preference by Aphelinus females for particular aphid species and instars reflect the outcome of behavioral interactions between the hosts and the parasites, rather than preference in the strict sense.     

Effects of host age on the performance of >Diadromus collaris, a pupal parasitoid of >Plutella xylostella

The ichneumonid >Diadromus collaris(Gravenhorst) (Hymenoptera: Ichneumonidae) is amajor solitary, pupal endoparasitoid of thediamondback moth, >Plutella xylostella(Linnaeus) (Lepidoptera: Plutellidae).Experiments to examine parasitism of the hostpupae of different ages by the parasitoid wereconducted in the laboratory. >Diadromuscollaris preferred host pupae that were in thefirst half of their pupal development. Survivalfrom larva to adult, and size and parasitizingcapacity of the resultant female adultsdecreased dramatically as host pupal ageincreased. When ovipositions were made intohost pupae that were in the last quarter oftheir development, all parasitoids died beforeadult emergence. The performance of >D.collaris, as affected by host pupal age,agrees with the simple diet theory thatpredicts female wasps should select hosts ofhigher nutritional quality for oviposition.     

Molecular diversity and relationships of North American Elymus trachycaulus and the Eurasian E. caninus species

The morphological similarity of Elymus trachycaulus to the Eurasian E. caninus has often been noted. This has lead to controversial and contradicting taxonomic treatments. Nevertheless, there has been no systematic investigation on molecular genetic similarity between E. trachycaulus and E. caninus. In this study, random amplified polymorphic DNA (RAPD) analysis was used to study the similarity between the two species. RAPD analysis of 38 samples representing E. caninus and E. trachycaulus complex yielded 111 interpretable RAPD bands. The Jaccard’s similarity values for E. caninus ranged from 0.38 between accessions H10345 and H10353 to 0.97 between accessions H8745 and H10096, with an average of 0.67. The Jaccard’s similarity values for E. trachycaulus complex ranged from 0.09 between E. trachycaulus ssp. subsecundus (PI 537321) and E. trachycaulus ssp. violaceus (PI 272612) to 0.78 between accessions PI 315368 and PI 372644, with an average of 0.43. The results from different analyses (NJ and PCA) were similar but not identical. The molecular genetic separation between E. caninus and E. trachycaulus was consistent. The PCA analysis clearly separated all E. caninus accessions from E. trachycaulus and its subspecies. The NJ analysis also showed separation between most accessions of E. caninus and E. trachycaulus. Further analysis excluding E. trachycaulus ssp. subsecundus and ssp. violaceus revealed that E. caninus species and E. trachycaulus species were clearly separated into two distinct groups. The RAPD data thus support the treatment of E. caninus and E. trachycaulus as distinct species. The analyses further indicate that E. violaceus is nested within E. trachycaulus, and more related to E. trachycaulus complex rather than to E. caninus.     

Population growth rate and relative virulence of the two South African biotypes of Russian wheat aphid,Diuraphis noxia,and bird cherry‐oat aphid,Rhopalosiphum padi,on resistant and non‐resistant barley

In South Africa a new biotype of the Russian wheat aphid (RWA), Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae), RWASA2, has appeared which exhibits an improved performance compared to the original biotype (RWASA1) on wheat containing the Dn1 resistance gene. We examined population growth rates as well as damage caused by RWASA1 and RWASA2, in addition to a different aphid species, the bird cherry‐oat aphid (BCA), Rhopalosiphum padi L. (Hemiptera: Aphididae), on three RWA‐resistant barley [Hordeum vulgare L. (Poaceae)] lines (STARS‐9577B, STARS‐0502B, and STARS‐9301B) and one susceptible control (PUMA). RWASA2 had a higher reproductive rate than RWASA1 on all barley lines tested, which is consistent with previous results on wheat. Two of the RWA‐resistant lines (STARS‐0502B and STARS‐9301B) also exhibited a similar resistance phenotype against BCA. In our experiments, severe chlorosis and leaf roll appeared earlier on the control PUMA barley variety as a result of RWASA2 feeding than was the case with RWASA1, probably due to the differences in reproductive rate. Although chlorosis appeared earlier on resistant plants after RWASA2 feeding, this symptom developed much faster during RWASA1 feeding on all three resistant lines tested. As chlorosis did not correlate well with aphid population numbers, we surmise that the differential chlorosis effects may be related to differences in the amount of saliva introduced by the two aphid clones during feeding. Our results indicate that the difference between RWASA2 and RWASA1 are broader than a ‘gene for gene’ interaction with the Dn1 resistance (R) gene in wheat, and that these biotypes also differ in important aspects of their biology.     

Reproductive compatibility and genetic variation between two strains of Aphelinus albipodus (Hymenoptera: Aphelinidae), a parasitoid of the soybean aphid, Aphis glycines (Homoptera: Aphididae)

Aphelinus albipodus Hayat and Fatima is a potential biological control agent of the soybean aphid, Aphis glycines Matsumura, which is a newly introduced soybean pest in the United States. We compared the reproductive compatibility and molecular genetic variation between two geographic strains of A. albipodus. One strain was collected from soybean aphids in Japan and the other recovered from Russian wheat aphid, Diuraphis noxia (Mordvilko), in the western U.S., populations of which were established with parasitoids imported from Eurasia. We present results of crossing experiments between the two strains, genetic differences based on RAPD-PCR markers, rDNA ITS1 and ITS2 gene sequences, and presence of Wolbachia in the two strains using PCR amplification of the wsp gene. We found no reduction in the production of females in reciprocal crosses between strains, but a significant reduction in fecundity when F₁ females stemming from one of the reciprocal crosses were backcrossed to males from either source. The two strains differed by 3.4% in the rDNA ITS1 sequence and by presence/absence of one RAPD-PCR marker from a total of 20 RAPD primers screened, but their rDNA ITS2 sequences were identical. We used restriction enzyme analysis to separate the strains by differential digestion of the ITS1 PCR product. Wolbachia was present in 100% of males and females of both strains of A. albipodus.     

Prevalence of full-size <Emphasis Type="Italic">P</Emphasis> and <Emphasis Type="Italic">KP</Emphasis> elements in North American populations of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

The P transposable element invaded the Drosophila melanogaster genome in the middle of the twentieth century, probably from D. willistoni in the Caribbean or southeastern North America. P elements then spread rapidly and became ubiquitous worldwide in wild populations of D. melanogaster by 1980. To study the dynamics and long-term fate of transposable genetic elements, we examined the molecular profile of genomic P elements and the phenotype in the P-M system of the current North American natural populations collected in 2001-2003. We found that full-size P and KP elements were the two major size classes of P elements present in the genomes of all populations ("FP + KP predominance") and that the P-related phenotypes had largely not changed since the 1980s. Both FP + KP predominance and phenotypic stability were also seen in other populations from other continents. As North American populations did not show many KP elements in earlier samples, we hypothesize that KP elements have spread and multiplied in the last 20 years in North America. We suggest that this may be due to a transpositional advantage of KP elements, rather than to a role in P-element regulation.     

Nutritional suitability and ecological relevance of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> and <Emphasis Type="Italic">Brassica oleracea</Emphasis> as foodplants for the cabbage butterfly, <Emphasis Type="Italic">Pieris rapae</Emphasis>

The thale cress, Arabidopsis thaliana, is considered to be an important model species in studying a suite of evolutionary processes. However, the species has been criticized on the basis of its comparatively small size at maturity (and consequent limitations in the amount of available biomass for herbivores) and on the duration and timing of its life cycle in nature. In the laboratory, we studied interactions between A. thaliana and the cabbage butterfly, Pieris rapae, in order to determine if plants are able to support the complete development of the herbivore. Plants were grown in pots from seedlings in densities of one, two, or four per pot. In each treatment, one, two, or five newly hatched larvae of P. rapae were placed on fully developed rosettes of A. thaliana. In a separate experiment, the same densities of P. rapae larvae were reared from hatching on single mature cabbage (Brassica oleracea) plants. Pupal fresh mass and survival of P. rapae declined with larval density when reared on A. thaliana but not on B. oleracea. However, irrespective of larval density and plant number, some P. rapae were always able to complete development on A. thaliana plants. A comparison of the dry mass of plants in different treatments with controls (= no larvae) revealed that A. thaliana partially compensated for plant damage when larval densities of P. rapae were low. By contrast, single cress plants with 5 larvae generally suffered extensive damage, whereas damage to B. oleracea plants was negligible. Rosettes of plants that were monitored in spring, when A. thaliana naturally grows, were not attacked by any insect herbivores, but there was often extensive damage from pulmonates (slugs and snails). Heavily damaged plants flowered less successfully than lightly damaged plants. Small numbers of generalist plant-parasitic nematodes were also recovered in roots and root soil. By contrast, plants monitored in a sewn summer plot were heavily attacked by insect herbivores, primarily flea beetles (Phyllotreta spp.). These results reveal that, in natural populations of A. thaliana, there is a strong phenological mismatch between the plant and most of its potential specialist insect herbivores (and their natural enemies). However, as the plant is clearly susceptible to attack from non-insect generalist invertebrate herbivores early in the season, these may be much more suitable for studies on direct defense strategies in A. thaliana.     

Recognition of heterospecific parasitism: Competition between Aphidiid (Aphidius ervi) and Aphelinid (Aphelinus asychis) parasitoids of Aphids (Hymenoptera: Aphidiidae; Aphelinidae)

The solitary parasitoids Aphidius erviHaliday (Hymenoptera: Aphidiidae) and Aphelinus asychisWalker (Hymenoptera: Aphelinidae) attacked but generally did not oviposit in pea aphids parasitized by the other species. Wasps selectively oviposited in unparasitized hosts when given a choice. Host discrimination depended on the recognition of internal cues. Females of A. asychiseither could not recognize or ignored A. ervi'sexternal host marking pheromone. Under most conditions, A. ervisurvived in superparasitized hosts, killing competing A. asychislarvae by physical attack and possibly physiological suppression. The outcome of larval competition was not affected by oviposition sequence or age difference between larvae; A. asychissurvived only when it had substantially completed larval development before the host was superparasitized by A. ervi.It is suggested that competition for host resources incurs a cost, for the winner in terms of reduced size or increased development time and for the loser in terms of lost progeny and searching time. Consequently, heterospecific host discrimination can be functional. Internal, and probably general, cues enable wasps to recognize and avoid oviposition in hosts already parasitized by an unrelated species.     

Photoperiodic and Thermal Regulation of Development and Cold Hardiness in Larvae of the Clover Leaf Weevil, Hypera punctata

Effects of photoperiod and temperature on the development and cold hardiness were investigated in larvae of Hypera punctata. At a relatively low temperature (15°C), the larvae fed less and developed more slowly under a 12L:12D (SD) photoperiod than under a 16L:8D photoperiod (LD). SD larvae had lower gut weight against the whole body weight and lower supercooling point (SCP) than the LD counterparts for the same instar and same body weight. This was because the larval SCP is markedly affected by the quantity of the gut content. Laboratory experiments indicated that the low temperature mortality of this larvae occurred mainly due to freezing irrespective of the photoperiod and temperature, suggesting that the lower lethal temperature (LLT) depends on the supercooling ability of larvae. The SD larvae tended to have a lower SCP and hence a lower LLT than the LD counterparts at 15 or 10°C, unlike at 20°C. Thus, the slower larval development under SD conditions at relatively low temperatures may prevent larvae from reaching the later instar, which have a higher SCP and thus less cold tolerance, during the coldest season. The suppressed feeding activity under SD conditions would lower the SCP, thereby reducing the possibility of lethal tissue freezing. Such a photoperiodic and thermal regulation of the larval development and the supercooling ability appear to represent adaptive mechanisms for winter survival in this beetle.     

Phylogeographic studies on natural populations of the South American fruit fly, <Emphasis Type="Italic">Anastrepha fraterculus</Emphasis> (Diptera: Tephritidae)

Anastrepha fraterculus is an important pest of commercial fruits in South America. The variability observed for morphological and behavioural traits as well as genetic markers suggests that A. fraterculus represents a complex of synmorphic species rather than a single biological species. We studied the correlation between geographical distribution and genetic variation in natural populations from Argentina and south Brazil. Fragments of the mitochondrial gene COII were sequenced in 28 individuals. The matrix of aligned sequences was phylogenetically analysed by parsimony, yielding a cladogram of haplotypes. Based on Templeton’s nested method, no clade showed any geographic pattern for the gene COII, indicating lack of significant association between haplotypic variability and geographic distribution. The analysis of nucleotide substitution distances by Neighbour-Joining algorithm showed that geographically distant populations exhibit low genetic distances. The corresponding trees clustered the populations without showing any geographic pattern. This result suggests that the populations studied are not reproductively isolated.     

Impact of single-gene and dual-gene Bt broccoli on the herbivore <Emphasis Type="Italic">Pieris rapae</Emphasis> (Lepidoptera: Pieridae) and its pupal endoparasitoid <Emphasis Type="Italic">Pteromalus puparum</Emphasis> (Hymenoptera: Pteromalidae)

Transgenic brassica crops producing insecticidal proteins from Bacillus thuringiensis (Bt) are being investigated as candidates for field release to control lepidopteran pests. Information on the potential impact of Bt brassica crops on pests and non-target natural enemies is needed as part of an environmental risk assessment prior to the commercial release. This first tier study provides insight into the tritrophic interactions among Bt broccoli plants, the herbivore Pieris rapae and its parasitoid Pteromalus puparum. We first evaluated the efficacy of three types of Bt broccoli plants, cry1Ac, cry1C and cry1Ac + cry1C, on different instars of P. rapae. Bt broccoli effectively controlled P. rapae larvae, although later instars were more tolerant. The efficacy of different Bt broccoli plants on P. rapae larvae was consistently cry1Ac > cry1Ac + cry1C > cry1C. When the parasitoid P. puparum developed in a P. rapae pupa (host) that had developed from Bt plant-fed older larvae, developmental time, total number and longevity of the P. puparum generated from the Bt plant-fed host were significantly affected compared with those generated from the non-Bt control plant-fed host. Simultaneously, negative effects on P. rapae pupae were found, i.e. pupal length, width and weight were significantly reduced after older P. rapae larvae fed on different Bt plants for 1 or 2 days. Cry1C toxin was detected using ELISA in P. rapae pupae after older larvae fed on cry1C broccoli. However, no Cry1C toxin was detected in newly emerged P. puparum adults developing in Bt-fed hosts. Only a trace amount of toxin was detected from entire P. puparum pupae dissected from the Bt plant-fed host. Moreover, no negative effect was found on the progeny of P. puparum developing from the Bt plant-fed host when subsequently supplied with a healthy host, P. rapae pupae. The reduced quality of the host appears to be the only reason for the observed deleterious effects on P. puparum. Our data suggest that the effects on P. puparum developing in Bt plant-fed P. rapae are mediated by host quality rather than by direct toxicity.