Effectiveness in the field of Bt rice lines against target pests under various cultural regimes

China has a long history of rice cultivation, incorporating several cultural practices known to influence damage by insect pests. Transgenic Bt rice expresses lepidopteran‐specific insecticidal proteins that primarily target lepidopteran insect pests. However, the effectiveness of Bt rice against target insect pests under different cultural regimes has not been evaluated. In this study, the effectiveness of Bt rice lines against rice leaffolder, Cnaphalocrocis medinalis (Guenée) (Lepidoptera: Pyralidae), and striped stem borer, Chilo suppressalis Walker (Lepidoptera: Crambidae), was evaluated under various transplanting densities, crop establishment methods, and planting times. The results showed that Bt rice lines (T2A‐1 and T1C‐19, containing Cry2A and Cry1C, respectively) could prevent damage by these target pests under a range of cultural practices. Injury by C. medinalis or C. suppressalis on rice did not differ with the rice lines under various transplanting densities. Direct‐seeded non‐Bt rice MH63 suffered heavier injury by C. medinalis and C. suppressalis than it did with transplanting, whereas injury to the two Bt rice lines did not differ with planting methods. Planting time significantly affected injury by C. medinalis or C. suppressalis on non‐Bt rice, whereas injury to Bt rice lines did not differ with planting time. These results suggest that transplanting density, planting method, and planting time did not significantly affect the resistance of two Bt rice lines, due to their high insecticidal activity against target insects.     

A single semi‐synthetic diet with improved antimicrobial activity for mass rearing of lepidopteran insect pests of cotton and maize

Helicoverpa armigera (Hübner), Earias vittella (Fabricius), Spodoptera litura (Fabricius), Spodoptera exigua (Hübner) (all Lepidoptera: Noctuidae), Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), and Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) are the major pests of cotton and maize. Mass‐rearing of these insects under controlled conditions is necessary to obtain the numbers needed to conduct bioassays to screen insecticides, proteins, and other compounds, as tools for insect pest management. We present a diet suitable for rearing the six lepidopteran pests (five cotton and one maize pest). We further show that this diet is on par with or superior to the published diet recipes for each of the insect species, which were studied for three generations. We also discuss the advantages of antimicrobials other than formalin for keeping microbial growth under check. A combination of antimicrobial solution and benomyl provided effective control and suppressed the growth of microbes for a longer period than a formalin‐containing diet. A common diet for six pests provide opportunities for automation of diet preparation in addition to improved throughput and consistency in the process, while eliminating diet‐batch related errors.     

Target and non‐target effects of a spider venom toxin produced in transgenic cotton and tobacco plants

The peptide ω‐Hexatoxin‐Hv1a (Hvt) is one of the most studied spider toxins. Its insecticidal potential has been reported against species belonging to the arthropod orders Lepidoptera, Diptera and Orthoptera. The gene encoding Hvt has been transformed into cotton and tobacco to protect the plants from damage by lepidopteran pests. This study evaluated the expression of the ω‐HXTX‐Hv1a gene in transgenic plants, and the toxicity of plant‐expressed and purified Hvt on target lepidopteran insects and on several non‐target species. Transgenic Bollgard II cotton plants, which produce Cry1Ac and Cry2Ab2 and purified Cry2Ab2 protein were included in the study as comparators. LC₉₅ values of purified Hvt against Spodoptera littoralis and Heliothis virescens were 28.31 and 27.57 μg/ml of artificial diet, respectively. Larval mortality was 100% on Hvt‐transgenic tobacco plants but not on Hvt‐transgenic cotton, probably because of the significantly lower toxin expression level in the transgenic cotton line. Non‐target studies were conducted with larvae of the predators Chrysoperla carnea and Coccinella septempunctata, adults of the aphid parasitoid Aphidius colemani, and adult workers of the honey bee, Apis mellifera. Even at 40 μg/ml, Hvt did not adversely affect the four non‐target species. Purified Cry2Ab2 at 10 μg/ml also did not adversely affect any of the non‐target species. Our results show that Hvt might be useful for developing insecticidal plant varieties to control pest Lepidoptera.     

Corn pith weevil,Geraeus penicillus (Coleoptera: Curculionidae), in transgenic,insect‐resistant and conventional field corn hybrids

The corn pith weevil Geraeus penicillus (Herbst) is occasionally found boring in corn stalks throughout the eastern and Midwestern United States. Injury caused by G. penicillus is not typically economical, but may be confused with that of the European corn borer Ostrinia nubilalis (Hubner), an important economic pest throughout the United States. During efforts to assess European corn borer infestations, we discovered G. penicillus in field corn in south‐eastern Pennsylvania, including hybrids genetically modified (i.e. Bt hybrids) to control European corn borer among other herbivore species. Our analysis across sites indicated that tunnels of G. penicillus were significantly more abundant in transgenic Bt hybrids than non‐Bt hybrids, but comparisons of Bt hybrids and their near isolines revealed mostly similar numbers of G. penicillus tunnels, suggesting other hybrid features might be affecting the distribution of G. penicillus. Tunnels of G. penicillus were equally distributed among the three transgenic trait packages represented in our study. In plants where we found G. penicillus, tunnels were more abundant in stalks free of European corn borer damage. Our report appears to be the first to note G. penicillus feeding in Bt corn hybrids. These findings are notable because they document insect damage in Bt hybrids that may be mistaken for European corn borer damage and may provide evidence of an insect herbivore proliferating following a mild winter or possibly even moving into competitor‐free space.     

New insights into an RNAi approach for plant defence against piercing‐sucking and stem‐borer insect pests

Insect double‐stranded (ds)RNA expression in transgenic crops can increase plant resistance to biotic stress; however, creating transgenic crops to defend against every insect pest is impractical. Arabidopsis Mob1A is required for organ growth and reproduction. When Arabidopsis roots were soaked in dsMob1A, the root lengths and numbers were significantly suppressed and plants could not bolt or flower. Twenty‐four hours after rice roots were immersed in fluorescent‐labelled dsEYFP (enhanced yellow fluorescent protein), fluorescence was observed in the rice sheath and stem and in planthoppers feeding on the rice. The expression levels of Ago and Dicer in rice and planthoppers were induced by dsEYFP. When rice roots were soaked in dsActin, their growth was also significantly suppressed. When planthoppers or Asian corn borers fed on rice or maize that had been irrigated with a solution containing the dsRNA of an insect target gene, the insect's mortality rate increased significantly. Our results demonstrate that dsRNAs can be absorbed by crop roots, trigger plant and insect RNAi and enhance piercing‐sucking and stem‐borer insect mortality rates. We also confirmed that dsRNA was stable under outdoor conditions. These results indicate that the root dsRNA soaking can be used as a bioinsecticide strategy during crop irrigation.     

Preference of Bt‐resistant and susceptible Busseola fusca moths and larvae for Bt and non‐Bt maize

The sustainability of genetically engineered insecticidal Bacillus thuringiensis Berliner (Bt) maize, Zea mays L. (Poaceae), is threatened by the evolution of resistance by target pest species. Several Lepidoptera species have evolved resistance to Cry proteins expressed by Bt maize over the last decade, including the African maize stem borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae). The insect resistance management (IRM) strategy (i.e., the high‐dose/refuge strategy) deployed to delay resistance evolution is grounded on certain assumptions about the biology and ecology of a pest species, for example, the interactions between the insect pest and crop plants. Should these assumptions be violated, the evolution of resistance within pest populations will be rapid. This study evaluated the assumption that B. fusca adults and larvae select and colonize maize plants at random, and do not show any preference for either Bt or non‐Bt maize. Gravid female B. fusca moths of a resistant and susceptible population were subjected to two‐choice oviposition preference tests using stems of Bt and non‐Bt maize plants. Both the number of egg batches as well as the total number of eggs laid on each stem were recorded. The feeding preference of Bt‐resistant and susceptible neonate B. fusca larvae were evaluated in choice test bioassays with whorl leaf samples of specific maize cultivars. Although no differential oviposition preference was observed for either resistant or susceptible female moths, leaf damage ratings indicated that neonate larvae were able to detect Bt toxins and that they displayed feeding avoidance behaviour on Bt maize leaf samples.     

Trichogramma parasitoids for control of Lepidopteran borers in Taiwan: species,life‐history traits and Wolbachia infections

Trichogramma, polyphagous endoparasitoids of lepidopteran eggs, are used against a variety of crop pests throughout the world including those of sugar cane and corn in south‐eastern Asia. Their ability to be easily and economically reared on factitious hosts and their wide host range have contributed to their widespread use in pest control. The overall aim of this study was to select strains for eventual release in crop areas for control of lepidopteran borer pests of sugar cane and corn. To this end, we identified common Trichogramma species emerging from corn borer egg masses throughout south‐western Taiwan, compared their life‐history characteristics, assessed their thermal limits and identified the Wolbachia infection status of collected Trichogramma parasitoids. Trichogramma ostriniae was the most commonly collected species on corn, with occasional detection of T. chilonis and an unidentified species designated as T. sp. y. Although the sex ratio varied widely between sites, Wolbachia infection was detected only at a single site in one species (T. ostriniae). Wolbachia‐infected T. ostriniae were tolerant to high temperature stress. Trichogramma chilonis had lowest fecundity of the three species tested, and a Wolbachia‐infected T. ostriniae strain had lower fecundity than an uninfected strain. Given the limited availability of distribution and historical data for Trichogramma species in Taiwan, the current study provides a baseline for future work and also highlights the importance of accurately identifying species when establishing colonies of natural enemies for biocontrol.     

Experimental warming increases herbivory by leaf‐chewing insects in an alpine plant community

Climate warming is predicted to affect species and trophic interactions worldwide, and alpine ecosystems are expected to be especially sensitive to changes. In this study, we used two ongoing climate warming (open‐top chambers) experiments at Finse, southern Norway, to examine whether warming had an effect on herbivory by leaf‐chewing insects in an alpine Dryas heath community. We recorded feeding marks on the most common vascular plant species in warmed and control plots at two experimental sites at different elevations and carried out a brief inventory of insect herbivores. Experimental warming increased herbivory on Dryas octopetala and Bistorta vivipara. Dryas octopetala also experienced increased herbivory at the lower and warmer site, indicating an overall positive effect of warming, whereas B. vivipara experienced an increased herbivory at the colder and higher site indicating a mixed effect of warming. The Lepidoptera Zygaena exulans and Sympistis nigrita were the two most common leaf‐chewing insects in the Dryas heath. Based on the observed patterns of herbivory, the insects life cycles and feeding preferences, we argue that Z. exulans is the most important herbivore on B. vivipara, and S. nigrita the most important herbivore on D. octopetala. We conclude that if the degree of insect herbivory increases in a warmer world, as suggested by this study and others, complex interactions between plants, insects, and site‐specific conditions make it hard to predict overall effects on plant communities.     

A selective insecticidal protein from Pseudomonas mosselii for corn rootworm control

The coleopteran insect western corn rootworm (WCR, Diabrotica virgifera virgifera) is an economically important pest in North America and Europe. Transgenic corn plants producing Bacillus thuringiensis (Bt) insecticidal proteins have been useful against this devastating pest, but evolution of resistance has reduced their efficacy. Here, we report the discovery of a novel insecticidal protein, PIP‐47Aa, from an isolate of Pseudomonas mosselii. PIP‐47Aa sequence shows no shared motifs, domains or signatures with other known proteins. Recombinant PIP‐47Aa kills WCR, two other corn rootworm pests (Diabrotica barberi and Diabrotica undecimpunctata howardi) and two other beetle species (Diabrotica speciosa and Phyllotreta cruciferae), but it was not toxic to the spotted lady beetle (Coleomegilla maculata) or seven species of Lepidoptera and Hemiptera. Transgenic corn plants expressing PIP‐47Aa show significant protection from root damage by WCR. PIP‐47Aa kills a WCR strain resistant to mCry3A and does not share rootworm midgut binding sites with mCry3A or AfIP‐1A/1B from Alcaligenes that acts like Cry34Ab1/Cry35Ab1. Our results indicate that PIP‐47Aa is a novel insecticidal protein for controlling the corn rootworm pests.     

‘Becoming a species by becoming a pest’ or how two maize pests of the genus Ostrinia possibly evolved through parallel ecological speciation events

New agricultural pest species attacking introduced crops may evolve from pre‐existing local herbivores by ecological speciation, thereby becoming a species by becoming a pest. We compare the evolutionary pathways by which two maize pests (the Asian and the European corn borers, ACB and ECB) in the genus Ostrinia (Lepidoptera, Crambidae) probably diverged from an ancestral species close to the current Adzuki bean borer (ABB). We typed larval Ostrinia populations collected on maize and dicotyledons across China and eastern Siberia, at microsatellite and mitochondrial loci. We found only two clusters: one on maize (as expected) and a single one on dicotyledons despite differences in male mid‐tibia morphology, suggesting that all individuals from dicotyledons belonged to the ABB. We found evidence for migrants and hybrids on both host plant types. Hybrids suggest that field reproductive isolation is incomplete between ACB and ABB. Interestingly, a few individuals with an ‘ABB‐like’ microsatellite profile collected on dicotyledons had ‘ACB’ mtDNA rather than ‘ABB‐like’ mtDNA, whereas the reverse was never found on maize. This suggests asymmetrical gene flow directed from the ACB towards the ABB. Hybrids and backcrosses in all directions were obtained in no‐choice tests. In laboratory conditions, they survived as well as parental strain individuals. In Xinjiang, we found ACB and ECB in sympatry, but no hybrids. Altogether, our results suggest that reproductive isolation between ACB and ABB is incomplete and mostly prezygotic. This points to ecological speciation as a possible evolutionary scenario, as previously found for ECB and ABB in Europe.     

Impacts of nitrogen fertilizer on major insect pests and their predators in transgenic Bt rice lines T2A‐1 and T1C‐19

Nitrogen is a critical factor for plant development and nitrogen input is one of the important tactics to enhance the development and yield of crops. Nevertheless, nitrogen input could influence the occurrence of insects positively or negatively. Nitrogen is also one of the main elements composing the insecticidal crystal (Cry) protein. Cry protein production could affect nitrogen partitioning in Bt plants and as such nitrogen input may influence insect pest management in transgenic Bt rice, Oryza sativa L. (Poaceae). To test this possibility, we evaluated the impacts of nitrogen regimes on the main insect pests and their predators on two Bt rice lines, T2A‐1 and T1C‐19, expressing Cry2A and Cry1C, respectively, and their non‐transgenic parental counterpart MH63. The results showed that Cry proteins with different nitrogen regimes have enough insecticidal activity on rice leaffolder, Cnaphalocrocis medinalis Guenée (Lepidoptera: Crambidae), in both laboratory and field experiments. Laboratory studies indicated that relevant parameters of ecological fitness in brown planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), a non‐target insect pest, were significantly affected by nitrogen input both on Bt and MH63 rice lines. Nymphal survival, female adult longevity, and egg hatchability in N. lugens differed significantly among rice varieties. The experiments conducted in rice fields also demonstrated that nitrogen was positively correlated with the abundance of N. lugens on Bt rice, similar to that on MH63 rice. The abundances of two predators – the wolf spider Pirata subpiraticus (Boesenberg & Strand) (Araneae: Lycosidae) and the bug Cyrthorhinus lividipennis Reuter (Hemiptera: Miridae) – were significantly affected by rice growth stages but not by nitrogen input and rice varieties. In conclusion, the above results indicate that high nitrogen regimes for Bt rice (T2A‐1 and T1C‐19) and non‐Bt rice (MH63) cannot facilitate the management of insect pests.     

Testing for host‐associated differentiation in two egg parasitoids of a forest herbivore

Several studies underline the importance of ecological barriers and differential selection in driving sympatric speciation. Host‐associated differentiation (HAD) has been proposed as one of the mechanisms leading to sympatric speciation. However, it is still unclear how common HAD is or which are the factors that could promote it. In particular, not much is known about HAD in predators and parasitoids of herbivorous insects. One of the characteristics postulated to pre‐dispose insects to HAD is parthenogenesis as it may favour adaptive responses to particular environments, amplifying selected gene complexes. In this study, we used amplified fragment length polymorphism (AFLP) markers to determine whether HAD is present in two parthenogenetic egg parasitoids attacking the same herbivore species – the pine processionary moth, Thaumetopoea pityocampa (Denis & Schiffermüller) (Lepidoptera: Notodontidae) – on two host Pinus species. A total of 100 loci for 59 individuals sampled in four populations of Baryscapus servadeii (Domenichini) (Hymenoptera: Eulophidae), a specialist parasitoid, and 106 loci for 117 individuals sampled in six populations of Ooencyrtus pityocampae Mercet (Hymenoptera: Encyrtidae), a generalist parasitoid, were analysed. Levels of genetic differentiation were also assessed with an outlier analysis, checking for alleles associated to host plants. No evidence of HAD was detected in any of the two parasitoid species. We hypothesize that both the lack of strict parthenogenetic reproduction and the ectophagous nature of the insect host could explain the absence of HAD. The genetic variation observed in the generalist parasitoid responded to a pattern of local adaptation, whereas no relationship with either host or geography was found in the specialist parasitoid.     

New and resurgent insect pests on low trellis hops

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Histories of host shifts and cospeciation among free‐living parasitoids of Rhagoletis flies

Host shifts by specialist insects can lead to reproductive isolation between insect populations that use different hosts, promoting diversification. When both a phytophagous insect and its ancestrally associated parasitoid shift to the same novel host plant, they may cospeciate. However, because adult parasitoids are free living, they can also colonize novel host insects and diversify independent of their ancestral host insect. Although shifts of parasitoids to new insect hosts have been documented in ecological time, the long‐term importance of such shifts to parasitoid diversity has not been evaluated. We used a genus of flies with a history of speciation via host shifting (Rhagoletis [Diptera: Tephritidae]) and three associated hymenopteran parasitoid genera (Diachasma, Coptera and Utetes) to examine cophylogenetic relationships between parasitoids and their host insects. We inferred phylogenies of Rhagoletis, Diachasma, Coptera and Utetes and used distance‐based cophylogenetic methods (ParaFit and PACo) to assess congruence between fly and parasitoid trees. We used an event‐based method with a free‐living parasitoid cost model to reconstruct cophylogenetic histories of each parasitoid genus and Rhagoletis. We found that the current species diversity and host–parasitoid associations between the Rhagoletis flies and parasitoids are the primary result of ancient cospeciation events. Parasitoid shifts to ancestrally unrelated hosts primarily occur near the branch tips, suggesting that host shifts contribute to recent parasitoid species diversity but that these lineages may not persist over longer time periods. Our analyses also stress the importance of biologically informed cost models when investigating the coevolutionary histories of hosts and free‐living parasitoids.     

A chromosome‐scale genome assembly of Antheraea pernyi (Saturniidae,Lepidoptera)

Antheraea pernyi is a semi‐domesticated lepidopteran insect species valuable to the silk industry, human health, and ecological tourism. Owing to its economic influence and developmental properties, it serves as an ideal model for investigating divergence of the Bombycoidea super family. However, studies on the karyotype evolution and functional genomics of A. pernyi are limited by scarce genomic resource. Here, we applied PacBio sequencing and chromosome structure capture technique to assemble the first high‐quality A. pernyi genome from a single male individual. The genome is 720.67 Mb long with 49 chromosomes and a 13.77‐Mb scaffold N50. Approximately 441.75 Mb, accounting for 60.74% of the genome, was identified as repeats. The genome comprises 21,431 protein‐coding genes, 85.22% of which were functionally annotated. Comparative genomics analysis suggested that A. pernyi diverged from its common ancestor with A. yamamai ~30.3 million years ago, and that chromosome fission contributed to the increased chromosome number. The genome assembled in this work will not only facilitate future research on A. pernyi and related species but also help to progress comparative genomics analyses in Lepidoptera.     

Food web associations and effect of trophic resources and environmental factors on parasitoids expanding their host range into non‐native hosts

Trophic interactions and environmental conditions determine the structure of food webs and the host expansion of parasitoids into novel insect hosts. In this study, we investigate plant–insect–parasitoid food web interactions, specifically the effect of trophic resources and environmental factors on the presence of the parasitoids expanding their host range after the invasion of Chrysodeixis chalcites (Esper) (Lepidoptera: Noctuidae). We also consider potential candidates for biological control of this non‐native pest. A survey of larval stages of Plusiinae (Lepidoptera: Noctuidae) and their larval parasitoids was conducted in field and vegetable greenhouse crops in 2009 and 2010 in various locations of Essex and Chatham‐Kent counties in Ontario, Canada. Twenty‐one plant–host insect–host parasitoid associations were observed among Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), C. chalcites, and larval parasitoids in three trophic levels of interaction. Chrysodeixis chalcites, an old‐world species that had just arrived in the region, was the most common in our samples. The larval parasitoids Campoletis sonorensis (Cameron) (Hymenoptera: Ichneumonidae), Cotesia vanessae (Reinhard), Cotesia sp., Microplitis alaskensis (Ashmead), and Meteorus rubens (Nees) (all Hymenoptera: Braconidae) expanded their host range into C. chalcites changing the structure of the food web. Copidosoma floridanum (Ashmead) (Hymenoptera: Encyrtidae) was the most common parasitoid of T. ni that was not found in the invasive species. Plant species, host abundance, and agro‐ecosystem were the most common predictors for the presence of the parasitoids expanding their host range into C. chalcites. Our results indicate that C. sonorensis, C. vanessae, and C. floridanum should be evaluated for their potential use in biological control of C. chalcites and T. ni.     

Inducible expression of a fusion gene encoding two proteinase inhibitors leads to insect and pathogen resistance in transgenic rice

Plant proteinase inhibitors (PIs) are considered as candidates for increased insect resistance in transgenic plants. Insect adaptation to PI ingestion might, however, compromise the benefits received by transgenic expression of PIs. In this study, the maize proteinase inhibitor (MPI), an inhibitor of insect serine proteinases, and the potato carboxypeptidase inhibitor (PCI) were fused into a single open reading frame and introduced into rice plants. The two PIs were linked using either the processing site of the Bacillus thuringiensis Cry1B precursor protein or the 2A sequence from the foot‐and‐mouth disease virus (FMDV). Expression of each fusion gene was driven by the wound‐ and pathogen‐inducible mpi promoter. The mpi‐pci fusion gene was stably inherited for at least three generations with no penalty on plant phenotype. An important reduction in larval weight of Chilo suppressalis fed on mpi‐pci rice, compared with larvae fed on wild‐type plants, was observed. Expression of the mpi‐pci fusion gene confers resistance to C. suppressalis (striped stem borer), one of the most important insect pest of rice. The mpi‐pci expression systems described may represent a suitable strategy for insect pest control, better than strategies based on the use of single PI genes, by preventing insect adaptive responses. The rice plants expressing the mpi‐pci fusion gene also showed enhanced resistance to infection by the fungus Magnaporthe oryzae, the causal agent of the rice blast disease. Our results illustrate the usefulness of the inducible expression of the mpi‐pci fusion gene for dual resistance against insects and pathogens in rice plants.