Control Of Lepidopteran Pests Research Articles

No Significant Impact of Transgenic Cry1Ab/1Ac Cotton on Rhizosphere‐Soil Enzyme Activities and Bacterial Communities

Core Ideas The selected enzymatic activities were not significantly affected by the GK 12. The bacterial population size was not significantly affected by the GK 12. The bacterial community structure was not significantly affected by the GK 12. Transgenic Bt‐cotton (Gossypium hirsutum L.) GK 12 is commonly used for control of lepidopteran pests in China, but concerns exist regarding possible unintended effects on soil microbial communities. Bacterial population sizes and community structures in the rhizosphere soil under intensive cultivation of GK 12, its near‐isogenic parent Simian 3 and a conventional cotton DP 5415 were analyzed during 2009 to 2011 by quantitative polymerase chain reaction (qPCR) and denaturing gradient gel electrophoresis (DGGE). Dehydrogenase, urease, and phosphatase activities were also measured. It was found that these microbial‐related parameters were significantly influenced by variations due to the year and plant growth stage. There were occasional differences in bacterial population size and community structures at some growth stages, but they were not manifested throughout the growing cycle and were not considered meaningful. Generally no significant differences were found in selected enzymatic activities, and bacterial population sizes and community structures in the rhizosphere soil of GK 12 and Simian 3. Three different species or bands were unique to GK 12 and Simian 3, but they were unamplifiable. The resolvable band profile or annotatable species composition was not different between GK 12 and Simian 3. Therefore, the data of this study did not show any significant and permanent impacts of Bt‐insertion in GK 12 on selected enzymatic activities, bacterial population size, and community structures in the rhizosphere soil during 3‐yr tests in northern China.

Discovery and quantitative structure-activity relationship study of lepidopteran HMG-CoA reductase inhibitors as selective insecticides.

In a previous study we have demonstrated that insect 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) can be a potential selective insecticide target. Three series of inhibitors were designed on the basis of the difference in HMGR structures from Homo sapiens and Manduca sexta, with the aim of discovering potent selective insecticide candidates. An in vitro bioassay showed that gem-difluoromethylenated statin analogues have potent effects on JH biosynthesis of M. sexta and high selectivity between H. sapiens and M. sexta. All series II compounds {1,3,5-trisubstituted [4-tert-butyl 2-(5,5-difluoro-2,2-dimethyl-6-vinyl-4-yl) acetate] pyrazoles} have some effect on JH biosynthesis, whereas most of them are inactive on human HMGR. In particular, the IC50 value of compound II-12 (37.8 nm) is lower than that of lovastatin (99.5 nm) and similar to that of rosuvastatin (24.2 nm). An in vivo bioassay showed that I-1, I-2, I-3 and II-12 are potential selective insecticides, especially for lepidopteran pest control. A predictable and statistically meaningful CoMFA model of 23 inhibitors (20 as training sets and three as test sets) was obtained with a value of q2 and r2 of 0.66 and 0.996 respectively. The final model suggested that a potent insect HMGR inhibitor should contain suitable small and non-electronegative groups in the ring part, and electronegative groups in the side chain. Four analogues were discovered as potent selective lepidopteran HMGR inhibitors, which can specifically be used for lepidopteran pest control. The CoMFA model will be useful for the design of new selective insect HMGR inhibitors that are structurally related to the training set compounds. © 2017 Society of Chemical Industry.

Evaluation of the Susceptibility Status of Spiny BollwormEarias biplaga(Walker) (Lepidoptera: Noctuidae) to Bt Cotton in South Africa

The bollworm complex of cotton in South Africa consists of the African bollworm, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae), red bollworm, Diparopsis castanea (Hamps.) (Lepidoptera: Noctuidae), and the spiny bollworms, Earias biplaga (Walker) (Lepidoptera: Noctuidae) and Earias insulana (Boisduval) (Lepidoptera: Noctuidae) (Green et al. 2003). Larvae of these species are regarded as major pests of cotton since they tunnel into the growing tips, flowering buds and cotton bolls, resulting in damage and subsequent yield losses (Bennett 2015). Genetically modified (GM) transgenic Bt cotton plants that express Cry proteins have been cultivated in SouthAfrica since 1998 to control these lepidopteran pests (Thirtleet al. 2003). Bollgard®, expressing the Cry1Ac protein, was first commercially produced in South Africa in 1998 and discontinued after the 2010 growing season (ICAC 2007). Bollgard ll®, also registered for control of lepidopteran pests on cotton, is a stacked transgenic cotton which expresses two Bt proteins, namely Cry1Ac and Cry2Ab2 (Taverniers et al. 2008; Showalter et al. 2009).

Toxicological Study and Oxidative Stress Evaluation for Safety Assessment of Bacillus thuringiensis Vip3Aa16 Toxin in Adult Mice

Vegetative insecticidal proteins were produced by some Bacillus thuringiensis strains and were successfully used in biological control against different agricultural pests such as Lepidoptera. To assess the safety of Vip3Aa16 toxins in mammalian organisms, we evaluated their toxicity using histological, hematological, and oxidative stress parameters on albino Swiss mice. The animals were orally treated with 2500, 5000, 7500 milligrams (mg) of the toxin/kilogram (kg) of body weight for 14 days. Then samples of blood, kidney and hepatic tissues were collected at the end of the treatment. Hematological parameters were monitored by RBC, WBC, hemoglobin, hematocrit, MCV, MCH, and MCHC. Liver and kidney MDA, SOD, vitamin C and H2O2 were analyzed to assess oxidative damage. Hepatotoxicity was monitored by analysis of the plasma enzymes ALT and AST and bilirubin levels. Renal toxicity was tested by urea, uric acid and creatinine evaluation. The histopathology of kidney and liver tissues was also investigated. The results of the toxicological study revealed that the Vip3AaA16 has no lethal effect since no mortality was observed at any dose. Moreover, body weight, hematological, histological, biochemical and oxidative findings showed no significant differences between treated and control groups. All these findings confirmed that this toxin is highly safe and doesn’t represent any risk on animal health and subsequently, Vip3Aa16 toxin can be safely used in biological programs to control Lepidopteran pests attacking crops around the world.

Transcriptomic response of wolf spider, Pardosa pseudoannulata, to transgenic rice expressing Bacillus thuringiensis Cry1Ab protein

BackgroundBacillum thuringiensis (Bt) toxin produced in Cry1-expressing genetically modified rice (Bt rice) is highly effective to control lepidopteran pests, which reduces the needs for synthetic insecticides. Non-target organisms can be exposed to Bt toxins through direct feeding or trophic interactions in the field. The wolf spider Pardosa pseudoannulata, one of the dominant predators in South China, plays a crucial role in the rice agroecosystem. In this study, we investigated transcriptome responses of the 5th instar spiders fed on preys maintained on Bt- and non-Bt rice.ResultsComparative transcriptome analysis resulted in 136 differentially expressed genes (DEGs) between spiderlings preying upon N. lugens fed on Bt- and non-Bt rice (Bt- and non-Bt spiderlings). Functional analysis indicated a potential impact of Bt toxin on the formation of new cuticles during molting. GO and KEGG enrichment analyses suggested that GO terms associated with chitin or cuticle, including “chitin binding”, “chitin metabolic process”, “chitin synthase activity”, “cuticle chitin biosynthetic process”, “cuticle hydrocarbon biosynthetic process”, and “structural constituent of cuticle”, and an array of amino acid metabolic pathways, including “alanine, asparatate and glutamate metabolism”, “glycine, serine and theronine metabolism”, “cysteine and methionine metabolism”, “tyrosine metabolism”, “phenylalanine metabolism and phenylalanine”, and “tyrosine and tryptophan biosynthesis” were significantly influenced in response to Cry1Ab.ConclusionsThe Cry1Ab may have a negative impact on the formation of new cuticles during molting, which is contributed to the delayed development of spiderlings. To validate these transcriptomic responses, further examination at the translational level will be warranted.

Effects of Carriers, Emulsifiers, and Biopesticides for Direct Silk Treatments on Caterpillar Feeding Damage and Ear Development in Sweet Corn.

In the northeastern United States, control of Lepidopteran pests of sweet corn, particularly corn earworm [Helicoverpa zea (Boddie)], is difficult using organic methods. The direct application of corn oil and Bacillus thuringiensis (Bt) to corn silk has been shown to reduce ear damage from corn earworm in past studies; these studies sought to optimize this method by evaluating additional carrier and biopesticide mixtures that comply with the United States Federal Insecticide, Fungicide, and Rodenticide Act and National Organic Standards. Carriers, which are liquids used to dissolve the biopesticide and deliver it into the tip of the ear, may have phytotoxic or insecticidal properties. Experiments conducted from 2001 to 2005 evaluated caterpillar damage and ear development effects from carriers (vegetable and paraffinic oils and carrageenan), biopesticides (Bt, spinsosad, and neem), and three emulsifiers in various combinations when applied directly to the tips of the ears 5-7 d after silk initiation. There were no effects of emulsifiers on ear quality, except for slight reduction in caterpillar damage in one of the two years. There were no differences among corn, soy, canola, and safflower oils in corn earworm control or tip development. The carrageenan carrier had the least effect upon ear development as measured by the length of nonpollinated kernels at the tip, compared to corn oil or paraffinic oil (JMS Stylet Oil), which caused the greatest tip damage as well as an oily discoloration. The carrier-pesticide combinations with the best ear quality overall were spinosad in carrageenan or corn oil, and Bt in carrageenan.

Controlled-release of Bacillus thurigiensis formulations encapsulated in light-resistant colloidosomal microcapsules for the management of lepidopteran pests of Brassica crops.

Bacillus thuringiensis (B. t.) based formulations have been widely used to control lepidopteran pests in agriculture and forestry. One of their weaknesses is their short residual activity when sprayed in the field. Using Pickering emulsions, mixtures of spores and crystals from three B. t. serovars were successfully encapsulated in colloïdosomal microparticles (50 μm) using innocuous chemicals (acrylic particles, sunflower oil, iron oxide nanoparticles, ethanol and water). A pH trigger mechanism was incorporated within the particles so that B. t. release occurred only at pH > 8.5 which corresponds to the midgut pH of the target pests. Laboratory assays performed on Trichoplusia ni (T. ni) larvae demonstrated that the microencapsulation process did not impair B. t. bioactivity. The best formulations were field-tested on three key lepidopteran pests that attack Brassica crops, i.e., the imported cabbageworm, the cabbage looper and the diamondback moth. After 12 days, the mean number of larvae was significantly lower in microencapsulated formulations than in a commercial B. t. formulation, and the effect of microencapsulated formulations was comparable to a chemical pesticide (lambda-cyhalothrin). Therefore, colloïdosomal microcapsule formulations successfully extend the bioactivity of B. t. for the management of lepidopteran pests of Brassica crops.

Monitoring changes in the actinobacterial field communities present in the rhizosphere soil of a transgenic cotton producing Cry1Ab/Ac proteins

Abstract Transgenic cotton GK 12 producing Cry1Ab/Ac proteins can effectively control lepidopteran pests in agriculture. However, there are concerns that GK 12 has unintended side-effects on actinobacterial communities in the soil. Actinobacterial communities in the rhizosphere soil of cottons were analyzed by real-time PCR (qPCR) and denaturing gradient gel electrophoresis (DGGE) at different growth stages in three annual replications under field conditions. Population sizes and community structures of Actinobacteria were markedly affected by natural variations in years, growth stages and cultivars. No significant differences were found in population sizes (excepting at budding in 2009), community structures, and Shannon indices of Actinobacteria (excepting at budding in 2010) between the GK 12 and its non-transgenic parent Simian 3, although there were differences between the GK 12 and the conventional cotton DP 5415. Phylogenetic analysis of DGGE band sequences indicated that Cellulosimicrobium sp. and Rhodococcus sp. only occurred in the GK 12 and the Simian 3. The dominant Actinobacteria did not differ between the GK 12 and the Simian 3. In conclusion, the overall impacts of the GK 12 on actinobacterial communities in the rhizosphere soil, based on qPCR and DGGE, were not significant during three continuous years in northern China.

Avian pest control in vineyards is driven by interactions between bird functional diversity and landscape heterogeneity

Summary Insectivorous birds are increasingly recognized for the crucial pest control services they provide to agroecosystems. While both the foraging activity and functional diversity of birds are enhanced by multiscale habitat heterogeneity, little is known about how these relationships may influence avian top‐down control of insects. Specifically, interactive effects of bird community structure and habitat heterogeneity on pest control across spatial scales have rarely been explored. We sampled bird communities and measured avian predation on plasticine model prey, as a proxy for lepidopteran pest control, in 20 vineyards of south‐western France. Vineyards differed both in sward heterogeneity at the local scale and amount of surrounding semi‐natural habitats at the landscape scale. Functional diversity metrics and community‐weighted mean traits were computed for bird communities based on a species–trait table including diet, foraging method, nesting site, migration strategy, laying date, home range size, clutch size and body mass. We used mixed models to test for the interacting effects of habitat heterogeneity and bird functional diversity on avian predation rates of plasticine prey. Contrary to expectations, bird functional diversity decreased with landscape‐scale heterogeneity, but was higher in vineyards managed with heterogeneous sward structures. In contrast, foliage‐gleaning insectivores were more abundant in landscapes supporting more semi‐natural habitats, suggesting an increase in their contribution to pest control along the landscape heterogeneity gradient. Accordingly, we found that avian predation on plasticine prey increased with bird functional evenness both in more heterogeneous vineyards at the local scale and in landscape mosaics supporting more semi‐natural habitats. Synthesis and applications. Our study demonstrates that habitat heterogeneity at both local and landscape scales influenced avian insectivory in vineyard agroecosystems by interacting with bird community structure. It provides important insights for ecological intensification in vineyards, pointing out that management options need to be adapted to both the functional composition of local bird communities and landscape context. We suggest that both on‐field and off‐field management can be used to enhance natural pest control services provided by birds in vineyards, especially by favouring sward heterogeneity and patches of semi‐natural habitats within large vineyard stands at the landscape scale.

Natural parasitism by Trichogramma spp. in agroecosystems of the Mid-North, Brazil

ABSTRACT: The micro-hymenopterans of genus Trichogramma are eggs parasitoids used in the biological control of lepidopteran pests. The objectives of this study was to record the interaction of species of Trichogramma and their hosts on crops in the Mid-North, in the states of Maranhão and Piauí, Brazil. Lepidopteran eggs were sampled on crops and non-crops. Trichogramma atopovirilia , T. manicobai , T. galloi and T. pretiosum occur naturally in eggs of eight lepidopteran species. Natural parasitism shown by Trichogramma species reveals the importance of these parasitoids as agents for biological control in the Mid-North region.

Parasitism and Suitability of Fertilized and Nonfertilized Eggs of the Rice Striped Stem Borer, Chilo suppressalis (Lepidoptera: Crambidae), for Trichogramma Parasitoids.

Trichogramma spp. are egg parasitoids largely used worldwide for biological control of lepidopteran pests. Host quality (related to host size and age, host species, etc.) can influence parasitism preference and fitness of the parasitoid offspring. However, few studies have documented the performance of Trichogramma parasitoids when they parasitize nonfertilized eggs of their lepidopteran hosts. In the present study, we investigated the performance of three indigenous Trichogramma species ( Trichogramma japonicum Ashmead, Trichogramma dendrolimi Matsumura, and Trichogramma chilonis Ishii) on fertilized and nonfertilized eggs of their native host, Chilo suppressalis (Walker). The results showed that the three Trichogramma species tested could recognize fertilized and nonfertilized eggs of C. suppressalis . The different fertilization status eggs of C. suppressalis were all accepted by T. japonicum , T. chilonis , and T. dendrolimi with a clear tendency that they preferred to parasitize fertilized eggs whether under no-choice or choice conditions. All Trichogramma species successfully completed development in parasitized eggs of C. suppressalis regardless if the host eggs were fertilized or not. There was similar adult emergence rate, development time, and female progeny between fertilized and nonfertilized eggs for all Trichogramma species with an exception of development for T. chilonis . Trichogramma chilonis had shorter developmental time in fertilized eggs than in nonfertilized ones. Whether in fertilized or nonfertilized eggs, T. dendrolimi had longer development time than other two Trichogramma species. However, T. dendrolimi had the largest percentage of female progeny on fertilized eggs, followed by T. japonicum , and T. chilonis had the least percentage of female progeny. The present study indicates that Trichogramma parasitoids (i) can distinguish fertilized vs. nonfertilized host eggs, and (ii) could use nonfertilized host eggs for successful offspring development (despite showing lower preference for such eggs) [corrected].

A comparative study of two-line early season hybrid rice with lepidopteran resistance

In our previous study, an early season rice restorer line B2A68 expressing Cry2Aa# gene was obtained. In order to evaluate the performance of B2A68’s hybrids, a total of six hybrids from crossing B2A68 with six thermo-sensitive genic male sterile (TGMS) lines of early season rice were compared for expression level of Cry2Aa protein, as well as in insect resistance, agronomic traits and grain quality with their non-Bt null controls. Our results showed that the highest Cry2Aa protein content among B2A68's hybrids was detected in leaf, where the Cry2Aa content was nearly three times of that in stem. The Cry2Aa content of B2A68 was significantly higher than those of its derived hybrids, indicating the Cry2Aa# gene was incompletely dominant in hybrids. The hybrids with Cry2Aa# gene exhibited higher plant protection against rice leaf roller than the hybrids without Cry2Aa# gene in field. Significant differences were observed in plant height, panicle length, number of grains per panicle, seed set, 1000-grain weight and yield per plant between hybrids with Cry2Aa# gene and hybrids without Cry2Aa# gene in 2013 or 2014. There were significant differences in chalky grain rate and chalkiness degree between paternal lines B2A68 and D68, and between hybrids with Cry2Aa# gene and hybrids without Cry2Aa# gene. All of the differences in agronomic traits and grain quality varied among parental lines and hybrids. In this paper, three hybrids with high lepidopteran resistance, high yield, elite agronomic traits and acceptable grain quality was selected out, that could serve as elite resistant hybrids to control lepidopteran pests in early season rice production.

Evaluation of Insecticides for the Control of Lepidopteran Larvae in Sweet Corn, 2015: Table 1

The objective of this experiment was to assess the efficacy of insecticides for the control of lepidopteran pests of sweet corn in eastern Virginia. The experiment consisted of eight treatments arranged in an RCB design with four replicates. “Merit” sweet corn was planted on 12 Jul 2015 at the Virginia Tech Eastern Shore Agricultural Research and Extension Center in Painter, VA. Plots were two rows wide and 20-ft (6.1 m) long with no guard rows. Rows were planted on a …

Insect Resistance to Bacillus thuringiensis Toxin Cry2Ab Is Conferred by Mutations in an ABC Transporter Subfamily A Protein.

The use of conventional chemical insecticides and bacterial toxins to control lepidopteran pests of global agriculture has imposed significant selection pressure leading to the rapid evolution of insecticide resistance. Transgenic crops (e.g., cotton) expressing the Bt Cry toxins are now used world wide to control these pests, including the highly polyphagous and invasive cotton bollworm Helicoverpa armigera. Since 2004, the Cry2Ab toxin has become widely used for controlling H. armigera, often used in combination with Cry1Ac to delay resistance evolution. Isolation of H. armigera and H. punctigera individuals heterozygous for Cry2Ab resistance in 2002 and 2004, respectively, allowed aspects of Cry2Ab resistance (level, fitness costs, genetic dominance, complementation tests) to be characterised in both species. However, the gene identity and genetic changes conferring this resistance were unknown, as was the detailed Cry2Ab mode of action. No cross-resistance to Cry1Ac was observed in mutant lines. Biphasic linkage analysis of a Cry2Ab-resistant H. armigera family followed by exon-primed intron-crossing (EPIC) marker mapping and candidate gene sequencing identified three independent resistance-associated INDEL mutations in an ATP-Binding Cassette (ABC) transporter gene we named HaABCA2. A deletion mutation was also identified in the H. punctigera homolog from the resistant line. All mutations truncate the ABCA2 protein. Isolation of further Cry2Ab resistance alleles in the same gene from field H. armigera populations indicates unequal resistance allele frequencies and the potential for Bt resistance evolution. Identification of the gene involved in resistance as an ABC transporter of the A subfamily adds to the body of evidence on the crucial role this gene family plays in the mode of action of the Bt Cry toxins. The structural differences between the ABCA2, and that of the C subfamily required for Cry1Ac toxicity, indicate differences in the detailed mode-of-action of the two Bt Cry toxins.

Transgenic Cotton-Fed Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) Affects the Parasitoid Encarsia desantisi Viggiani (Hymenoptera: Aphelinidae) Development.

Cotton cultivars expressing Cry proteins are widely used to control lepidopteran pests. The effects of transgenic plants containing insecticidal Cry proteins on non-target species must be comprehended for a better and rational use of this technology for pest management. We investigated the influence of the Bt cotton cultivars NuOPAL and FM 975 on biological parameters of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), a non-target pest of Bt cotton cultivars and on its parasitoid Encarsia desantisi Viggiani (Hymenoptera: Aphelinidae). The experiments were conducted in a climatized room, and the non-transgenic near isolines were used for rearing whiteflies as control hosts. The effects of the Bt cotton cultivars on the period of embryonic and larval development and the percentage of adult emergence of B. tabaci were assessed. The period required for embryonic, larval, and pupal development and the percentage of emergence and longevity of E. desantisi females were determined using Bt cotton-fed and non-Bt cotton-fed B. tabaci as hosts. Both Bt cotton cultivars resulted in a decrease of approximately 20% of adult emergence of B. tabaci. Differently, an increase of approximately 10% of adult emergence of E. desantisi was observed for parasitoids that used hosts fed with both Bt cotton cultivars. However, female parasitoid longevity decreased when their hosts were fed on Bt cotton cultivars. Our data suggest that the use of Bt cotton cultivars in association with the biological control agent E. desantisi could be functional for the management of B. tabaci in Bt cotton crops.

Effects of Trichoderma viride chitinases on the peritrophic matrix of Lepidoptera.

The peritrophic matrix (PM) is formed by a network of chitin fibrils associated with proteins, glycoproteins and proteoglycans that lines the insect midgut. It is a physical barrier involved in digestion processes, and protects the midgut epithelium from food abrasion, pathogen infections and toxic materials. Given its fundamental role in insect physiology, the PM represents an excellent target for pest control strategies. Although a number of viral, bacterial and insect chitinolytic enzymes affecting PM integrity have already been tested, exploitation of fungal chitinases has been almost neglected. Fungal chitinases, already in use as fungal phytopathogen biocontrol agents, are known to attack the insect cuticle, but their action on the insect gut needs to be better investigated. In the present paper, we performed a biochemical characterisation of a commercial mixture of chitinolytic enzymes derived from Trichoderma viride and analysed its in vitro and in vivo effects on the PM of the silkworm Bombyx mori, a model system among Lepidoptera. We found that these enzymes have significant in vitro effects on the structure and permeability of the PM of this insect. A bioassay supported these results and showed that the oral administration of the mixture causes PM alterations, leading to adverse consequences on larval growth and development, negatively affecting pupal weight and even inducing mortality. This study provides an integrated experimental approach to evaluate the effects of fungal chitinases on Lepidoptera. The encouraging results obtained herein make us confident about the possible use of fungal chitinases to control lepidopteran pests.

MiR-2 family targets awd and fng to regulate wing morphogenesis in Bombyx mori

MicroRNAs (miRNAs) are post-transcriptional regulators that target specific mRNAs for repression and thus play key roles in many biological processes, including insect wing morphogenesis. miR-2 is an invertebrate-specific miRNA family that has been predicted in the fruit fly, Drosophila melanogaster, to be involved in regulating the Notch signaling pathway. We show here that miR-2 plays a critical role in wing morphogenesis in the silkworm, Bombyx mori, a lepidopteran model insect. Transgenic over-expression of a miR-2 cluster using a Gal4/UAS system results in deformed adult wings, supporting the conclusion that miR-2 regulates functions essential for normal wing morphogenesis. Two genes, abnormal wing disc (awd) and fringe (fng), which are positive regulators in Notch signaling, are identified as miR-2 targets and validated by a dual-luciferase reporter assay. The relative abundance of both awd and fng expression products was reduced significantly in transgenic animals, implicating them in the abnormal wing phenotype. Furthermore, somatic mutagenesis analysis of awd and fng using the CRISPR/Cas9 system and knock-out mutants also resulted in deformed wings similar to those observed in the miR-2 overexpression transgenic animals. The critical role of miR-2 in Bombyx wing morphogenesis may provide a potential target in future lepidopteran pest control.

Isolation and Characterization of New Bacillus thuringiensis Strains with Insecticidal Activity to Difficult to Control Lepidopteran Pests

Isolation and Characterization of New Bacillus thuringiensis Strains with Insecticidal Activity to Difficult to Control Lepidopteran Pests

Maternal thermal effect on diapause inTrichogrammaspecies (Hymenoptera: Trichogrammatidae)

AbstractBoth direct thermal and maternal photoperiodic effects on diapause induction have been thoroughly investigated in many insect species, while maternal thermal effects have been infrequently studied. We studied the effect of temperature during development of maternal generation on the proportion of diapausing progeny in four species of the genusTrichogrammaWestw., minute egg parasitoids, widely used for biological control of lepidopteran pests. The maternal generations were reared at day lengths of 12 and 18 h and temperatures of 17, 20, 25 and 30°C, and their progeny developed under day length of 12 h and temperatures of 13 and 14°C. InT. evanescensandT. piceum, the proportion of diapausing progeny decreased with increasing temperature under all tested photoperiods and thermal regimes of progeny development; the high temperature of 30°C totally averted diapause of progeny. InT. buesiandT. principium,low temperatures of 17 and 20°C resulted in relatively high proportion of diapausing progeny only when the maternal generation developed under short‐day conditions. The threshold of the maternal thermal response varied from 17–18 to 22–23°C. Under field conditions,Trichogrammafemales are exposed to such high temperatures only during summer, when diapause in their progeny is in any case prevented by the maternal photoperiodic response and by the thermal response of the larvae. We conclude that the maternal thermal effect on diapause induction, although to a different extent, is inherent toTrichogrammaspecies but, at least as suggested by laboratory experiments, it does not play any role in the regulation of seasonal development under natural conditions. However, during mass rearing ofTrichogrammawasps, it should be taken into account that high temperature, even when combined with short photoperiod, can avert diapause in the next generation.

Systemic application of chlorantraniliprole to cabbage transplants for control of foliar-feeding lepidopteran pests

The diamide insecticide chlorantraniliprole is registered for control of lepidopteran pests in cabbage (Brassica oleracea L.). Taking advantage of its root-uptake systemic properties, chlorantraniliprole is labeled for use with a variety of soil application methods in different countries, depending on pests and local practices. We investigated the efficacy of different cabbage transplant application methods using a leaf consumption bioassay. In the laboratory, we compared different transplant water volumes, characterized the effect of transplant plug size when the insecticide is applied by drenching or soaking the seedling tray, and determined the effect of different soil types. At three field sites, we compared the efficacy of chlorantraniliprole applied in transplant water or as a tray drench or tray soak treatment. In the laboratory, transplant water volume did not affect the level or duration of Trichoplusia ni (Hübner) mortality caused by chlorantraniliprole. When seedling trays were drenched with insecticide solution, transplant plug size did not affect mortality, but when trays were soaked with an equivalent volume of solution, mortality was higher with small plugs. Transplanting plugs treated by transplant water, drench or soak into different soil types did not affect mortality caused by chlorantraniliprole. In the field, transplant water application was the most effective method at all three locations. Tray soak was the most variable application method. Different application methods can be used to take advantage of the systemic characteristics of chlorantraniliprole. Among the methods tested, transplant water and tray drench resulted in more consistent mortality under variable field conditions.