Maize Borer Research Articles

Dynamic trends in maize diseases and pests across six regions in China over two decades

Maize production faces persistent threats from maize diseases and pests (MDPs) throughout its growth cycle, posing substantial risks to food security. However, understanding the spatio-temporal dynamics of MDPs occurrences on a regional scale has remained elusive due to a lack of continuous observation data. This study curated a comprehensive dataset spanning two decades, from 1999 to 2018, across six key maize planting regions in China [Spring sown area in Northern China (1-NC), Summer sown region in Huang-Huai-Hai Plain (2-HHP), Southwest Mountain Maize Region (3-SM), Southern Hilly Maize Region (4-SH), Northwest Irrigated Maize Region (5-NI), and Maize Region in Qinghai-Tibet Plateau (6-QTP)]. The average extent of MDP occurrence in 1-NC and 2-HHP exceeded that in other regions over the two-decade period. Furthermore, the occurrence of MDPs exhibited a substantial increase in 1-NC, 2-HHP, 3-SM, 4-SH, and 5-NI over the same period. Meanwhile, the average occurrence intensity of MDPs in 2-HHP surpassed that in other regions. Notably, maize leaf blight and the Asian maize borer emerged as predominant diseases and pests in 1-NC, 2-HHP, 3-SM, 4-SH, and 5-NI. A bivariate trend analyses highlighted a notable increase in the species count for both the extent and intensity of MDP occurrences, including double-spotted leaf beetle in 1-NC, and cotton bollworm in 2-HHP. This extensive, long-term analysis offers a foundation for devising comprehensive strategies for MDP control on a national scale, enabling the formulation of tailored forecasting and control measures across six planting regions.

Identification and Evaluation of Insect and Disease Resistance in Transgenic Cry1Ab13-1 and NPR1 Maize

PCR detection, quantitative real-time PCR (q-RTPCR), outdoor insect resistance, and disease resistance identification were carried out for the detection of genetic stability and disease resistance through generations (T2, T3, and T4) in transgenic maize germplasms (S3002 and 349) containing the bivalent genes (insect resistance gene Cry1Ab13-1 and disease resistance gene NPR1) and their corresponding wild type. Results indicated that the target genes Cry1Ab13-1 and NPR1 were successfully transferred into both germplasms through tested generations; q-PCR confirmed the expression of Cry1Ab13-1 and NPR1 genes in roots, stems, and leaves of tested maize plants. In addition, S3002 and 349 bivalent gene-transformed lines exhibited resistance to large leaf spots and corn borer in the field evaluation compared to the wild type. Our study confirmed that Cry1Ab13-1 and NPR1 bivalent genes enhanced the resistance against maize borer and large leaf spot disease and can stably inherit. These findings could be exploited for improving other cultivated maize varieties.

Trophic attractiveness for soil fauna of residues of Bt and near-isogenic maize: a C and N stable isotope-based study

Genetically modified (GM) crops are considered a good way to reduce insecticide use and the presence of certain agricultural pests, thus improving food and environmental safety. Nevertheless, effects of GM plant residues on the soil food web are still poorly understood. Zea mays L., enriched with a gene from Bacillus thuringiensis Berliner subsp. kurstaki (Bt) as a defence against the maize borer, is widely cultivated. In this study, we explored the invertebrate food webs associated with residues of Bt and non-Bt maize, respectively represented by DKC6575, with a Cry1Ab transgene (event MON810), and its near-isogenic Tietar variety, in a five-month field experiment. C and N stable isotopes and Bayesian mixing models were used to assess trophic niche metrics and track nutrient flows from maize residues and weeds occurring in maize crops to invertebrate detritivores and predators. While there were no initial differences in the structural components of maize residues between varieties, after five months of exposure in the field, the lignin content was higher and the organic matter content was lower in non-Bt than in Bt maize. Organic matter depletion over time was associated with a decrease in primary consumer abundance and an increase in their trophic niche width in both Bt and non-Bt maize, but it was faster in the former. The abundance of primary consumers and predators was higher in non-Bt than in Bt maize, but the distribution of organisms across trophic levels differed between varieties, with prey availability being lower in non-Bt than in Bt maize. This allowed Bt-associated predators to maintain a diet based primarily on the maize food chain throughout the experimental period. In contrast, non-Bt-associated predators were more dependent on weed-feeding prey by the end of the experiment, increasing the coupling between the maize and weed energy channels in the soil food web. Some taxon-specific effects were evident. Less vagile organisms such as Diptera had a specific diet mostly related to maize regardless of variety and time, while the diets of more vagile organisms like Coleoptera and Opiliones changed the most over time. Overall, our results suggest that the attractiveness of non-Bt maize residues for invertebrate consumers is higher than the Bt variety, although the higher recalcitrant content following decomposition reduces it over time. The attractiveness also affects the movement of invertebrate predators (potentially including pest control agents) and thus nutrient flows in tri-trophic detritus-based food webs in cultivated and uncultivated plots.

Optimization of aviation adjuvants based on wettability analysis for insecticide application on maize using UAV

Adjuvants can increase the control efficacy of diseases and insect pests by changing the physico-chemical properties of pesticides. Most of the aviation spray adjuvants are versions of ground adjuvants. Maize insecticide sprays with unmanned aerial vehicles (UAV), have problems such as relatively low droplet deposition rate and poor wettability. Hence, wettability research and optimization tests for aviation spray adjuvants are needed. The present study screened 12 spray adjuvants using physico-chemical property experiments. The adjuvants were applied to improve the droplet deposition and control efficacy in maize borers controlling by UAV. The selected spray adjuvants were Po2 (a hyperbranched polymer adjuvant) and VO3 (a vegetable oil adjuvant). Results showed that, (1) When Po2 was added in water-dispersible granules (WGs) at volume rate of 12 L/hm2, the dynamic surface tension (DST) of WGs was decreased by 37.41%, and the maize leaves were covered by droplets 100%, the droplet deposition was increased by 104% and maize borer control was increased by 46%; (2) VO3 decreased the surface tension of ultra-low-volume (ULV) formulation by 12.02% and the maize leaves were covered by droplets 100%. The effect of VO3 on improving the droplet deposition and control efficacy at 12 L/hm2 with ULV was not significant. Thus, the addition of aviation spray adjuvant to improve the wettability of WGs significantly improved the droplet deposition and control efficacy but it had no significant effect on the ULV formulation. Keywords: unmanned aerial vehicles, spray adjuvants, wettability, maize insecticide application DOI: 10.25165/j.ijabe.20211405.6605 Citation: Zang Y, Zhou Z Y, Zang Y, Luo X Y, Liao J, Ming R, et al. Optimization of aviation adjuvants based on wettability analysis for insecticide application on maize using UAV. Int J Agric & Biol Eng, 2021; 14(5): 11–18.

Transport and instream removal of the Cry1Ab protein from genetically engineered maize is mediated by biofilms in experimental streams.

The majority of maize planted in the US is genetically-engineered to express insecticidal properties, including Cry1Ab protein, which is designed to resist the European maize borer (Ostrinia nubilalis). After crop harvest, these proteins can be leached into adjacent streams from crop detritus left on fields. The environmental fate of Cry1Ab proteins in aquatic habitats is not well known. From June-November, we performed monthly short-term additions of leached Cry1Ab into four experimental streams with varying benthic substrate to estimate Cry1Ab transport and removal. At the start of the experiments, when rocks were bare, we found no evidence of Cry1Ab removal from the water column, but uptake steadily increased as biofilm colonized the stream substrate. Overall, Cry1Ab uptake was strongly predicted by measures of biofilm accumulation, including algal chlorophyll a and percent cover of filamentous algae. Average Cry1Ab uptake velocity (vf = 0.059 ± 0.009 mm s-1) was comparable to previously reported uptake of labile dissolved organic carbon (DOC; mean vf = 0.04 ± 0.008 mm s-1). Although Cry1Ab has been shown to rapidly degrade in stream water, benthic biofilms may decrease the distance proteins are transported in lotic systems. These results emphasize that once the Cry1Ab protein is leached, subsequent detection and transport through agricultural waterways is dependent on the structure and biology of receiving stream ecosystems.

Carotenoids moderate the effectiveness of a Bt gene against the European corn borer, Ostrinia nubilalis.

We assessed the effectiveness of a biofortified maize line (4BtxHC) which accumulates high levels of antioxidant carotenoids that also expressed the insecticidal Cry1Ac Bacillus thuringiensis (Bt) gene against the European corn borer Ostrinia nubilalis. This line had been previously engineered to accumulate carotenoids specifically in the seed endosperm, whereas the Bt gene was expressed constitutively. The concentrations of Bt toxin (Cry 1Ac) in the leaves of the 4Bt and 4BtxHC lines were not significantly different at 47±6 μg/g of fresh weight (FW); neither were they in the kernels of both lines (35±3 μg/g FW). The kernels and leaves were toxic to the larvae of O. nubilalis. However, the insecticidal activity was substantially lower (ca. 20%) than that of lines that expressed only Bt in spite that the two lines showed a quantity of toxin not significantly different in kernels or in leaves. Although the reduced effectiveness of Cry1Ac in kernels may not be entirely surprising, the observation of the same phenomenon in vegetative tissues was unexpected. When semi-artificial diets containing kernels from 4Bt supplemented with different levels of β-carotene were used in insect bioassays, the β-carotene moderated the effectiveness of the Bt similarly to the plant material with carotenoid enrichment. To elucidate the biochemical basis of the reduced effectiveness of Bt toxin in the carotenoid-enriched plants, we measured the activity of three enzymes known to be implicated in the detoxification defence, namely, catalase, superoxide dismutase and glutathione S-transferase. Whereas Cry1Ac expression significantly increased SOD and CAT enzymatic activity in the absence of carotenoids, carotenoids, either in 4BtxHC or in artificial diets enriched with β-carotene, significantly lowered CAT activity. Carotenoids can therefore moderate the susceptibility of the maize borer O. nubilalis to Cry1Ac, and we hypothesize that their role as antioxidants could explain this phenomenon via their scavenging of reactive oxygen species produced during Cry1Ac detoxification in the larvae. The involvement of this mechanism in the decreased mortality caused by Cry1Ac when carotenoids are present in the diet is discussed.

Assessment of the influence of fertilisation and environmental conditions on maize health

Field experiments showed the occurrence of such agrophages as the frit fly (Oscinella frit L.) and the European maize borer (Pyrausta nubilalis Hbn.). Identified diseases included fusariosis (Fusarium ssp.) and maize smut (Ustilago maydis Corda). The incidence of the frit fly was influenced by weather conditions, mainly temperature, in the period from sowing to the BBCH 15–16 phase. Moderate temperature conditions contributed to the occurrence of the pest. The significantly highest percentage of plants damaged by larvae of this pest was recorded on maize fertilised only with potassium (K) and phosphorus with potassium (PK). In turn, the lowest percentage of plants damaged by frit fly larvae was recorded for maize fertilised with nitrogen and potassium (NK). The percentage of plants damaged by the European maize borer was influenced by temperature and humidity conditions in individual years of the study. The highest percentage of plants damaged by larvae of the pest was found in the vegetation season characterised by the highest amount of rainfall with the lowest mean daily air temperature. The presence of potassium in a given fertiliser combination, the application of manure or combined application of manure and mineral fertilisation resulted in an enhanced resistance of maize plants to Fusarium ssp. fungi. The significantly greatest infestation of maize plants by the fungus Ustilago maydis Corda was recorded in the treatment in which only nitrogen was applied. In turn, the lowest percentage of plants with symptoms of this disease was recorded in the treatment with the application of potassium alone and in the application of potassium together with phosphorus.

The Cotesia sesamiae story: insight into host-range evolution in a Hymenoptera parasitoid and implication for its use in biological control programs.

This review covers nearly 20years of studies on the ecology, physiology and genetics of the Hymenoptera Cotesia sesamiae, an African parasitoid of Lepidoptera that reduces populations of common maize borers in East and South Africa. The first part of the review presents studies based on sampling of C. sesamiae from maize crops in Kenya. From this agrosystem including one host plant and three main host borer species, studies revealed two genetically differentiated populations of C. sesamiae species adapted to their local host community, and showed that their differentiation involved the joint evolution of virulence genes and sensory mechanisms of host acceptance, reinforced by reproductive incompatibility due to Wolbachia infection status and natural inbreeding. In the second part, we consider the larger ecosystem of wild Poales plant species hosting many Lepidoptera stem borer species that are potential hosts for C. sesamiae. The hypothesis of other host-adapted C. sesamiae populations was investigated based on a large sampling of stem borer larvae on various Poales across sub-Saharan Africa. The sampling provided information on the respective contribution of local hosts, biogeography and Wolbachia in the genetic structure of C. sesamiae populations. Molecular evolution analyses highlighted that several bracovirus genes were under positive selection, some of them being under different selection pressure in C. sesamiae populations adapted to different hosts. This suggests that C. sesamiae host races result from co-evolution acting at the local scale on different bracovirus genes. The third part considers the mechanisms driving specialization. C. sesamiae host races are more or less host-specialized. This character is crucial for efficient and environmentally-safe use of natural enemies for biological control of pests. One method to get an insight in the evolutionary stability of host-parasite associations is to characterize the phylogenetic relationships between the so-called host-races. Based on the construction of a phylogeny of C. sesamiae samples from various host- and plant species, we revealed three main lineages. Mechanisms of differentiation are discussed with regard to the geography and ecology of the samples. One of the lineage presented all the hallmarks of a distinct species, which has been morphologically described and is now studied in the perspective of being used as biological control agent against Sesamia nonagrioides Lefèbvre (Lepidoptera: Noctuidae), a major maize pest in West Africa and Mediterranean countries (see Benoist et al. 2017). The fourth part reviews past and present use of C. sesamiae in biological control, and points out the interest of such molecular ecology studies to reconcile biodiversity and food security stakes in future biological control.

Different IGRs concentrations against maize stem borer (Chilo partellus Swinhoe) in field condition of Faisalabad-Pakistan

The experiment was conducted at the Youngwala experimental area of the Department of Agri. Entomology, University of Agriculture, Faisalabad in a Randomized Complete Block Design (RCBD), with 24 treatments excluding one control. The data for maize stem borer population was recorded after 3 days, 7 days and 14 days post IGRs application. The results obtained are concluded that all the insect growth regulators were equally effective against maize stem borer at different concentrations and on the numerical basis lowest stem borer population and its infestation was recorded in the pyriproxyfen® and priority® at 2x concentration and at concentration of field recommended concentration followed by other treatments concentrations. So, among the entire tested insect growth regulators pyriproxyfen® and priority® were the most effective IGRs against maize borer. Among the entire tested insect growth regulators viper® and sitara® were the least effective IGRs against maize borer.

Economic evaluation of biorational and conventional insecticides for the control of maize stem borer Chilo partellus (Swinhoe) in Zea mays

Maize borer, Chilo partellus (Swinhoe) is the chief limiting factor for higher corn production. Field trials to assess the efficacy of different insecticides against C. partellus were carried in district Ropar, Punjab. It was observed that significantly lesser leaf injury incidence was recorded in biorational treatment T1: chlorantriniliprole 18.5 SC (3.43 & 4.23) in comparison to broad spectrum conventional insecticide treatment T3: Deltamethrin 2.8 EC (4.63& 5.36) and T4 :Farmer’s practice 4.43 and 6.93. Whereas in plots with parasitoid application (T2), the leaf injury incidence was recorded to be 6.56 & 7.86 during 2012 and 2013, respectively. Though T2 was statistically superior to control, however it was not at par with insecticide treatments. Furthermore similar trend was observed for dead hearts reduction in different treatments. It was recorded to be 3.16 and 3.90, 3.33 and 3.96, 3.53 and 3.96 in insecticide treatment plots T1, T3 and T4 respectively. The economic returns on the basis of marketable grain yield in insecticide treated plots was more in T1 followed by T3 and T4 (51.99, 49.58 and 48.51) in comparison to control (40.44) and biological control plots (46.75). Therefore experimental data revealed overall superiority of biorational pesticide in comparison to conventional insecticides for reduction in pest damage and economic returns. Hence the option of biorational for the control of maize stem borer not only justify safety to environment but also offers effective control of borer population in maize ecosystem due to its distinct chemical class and unique mode of action.

Damage of Maize Borer and Maize Weevil on the Yield of Transgenic Phytase Maize

The recent Chinese government approval of transgenic phytase maize for field experimentation is vital for its development of biotech maize for improved maize production. Phytase maize can potentially improve the efficiency of feed utilization by livestock and reduce environmental pollution from animal manure. Plant growth, phytochemistry, and economic characteristics of phytase maize were compared with non‐transgenic maize in field conditions. Population abundance and growth physiology of the maize borer (Ostrinia furnacalis) and the maize weevil (Sitophilus zeamais) were investigated during maize growing season and grain storage period, respectively, to assess insect pests’ occurrence and economic damage. Agronomic traits of phytase maize were generally superior to those of non‐transgenic maize, but the yield of phytase maize was only 5.5% higher than that of non‐transgenic maize. No significant difference in population dynamics of the maize borer was observed between them, while phytase maize significantly enhanced pupal weight and female fecundity of the maize borer. The length of the maize borer feeding tunnels in the stems was significantly greater in phytase maize. Moreover, significant increases in adult weight and population abundance of the maize weevil resulted in additional 2.98% losses for transgenic grains compared with non‐transgenic grains. Upon commercialization of transgenic maize in China, it will likely alter the arthropod population dynamics in the maize agroecosystem, increase plant susceptibility to lodging, and increase grain yield loss. Nevertheless, the increased insect‐induced loss (∼8%) in transgenic maize would likely be more than offset by enhanced phosphate utilization efficiency of livestock, when fed transgenic maize containing diet, and reduced environmental pollution from lower phosphate animal waste.

Baseline sensitivity of maize borers in India to the Bacillus thuringiensis insecticidal proteins Cry1A.105 and Cry2Ab2.

Among the major pests of maize in India are two stem borers, Chilo partellus (Swinhoe) and Sesamia inferens (Walker), and an earworm, Helicoverpa armigera (Hübner). As a pest control strategy, transgenic Bacillus thuringiensis (Bt) maize hybrids are undergoing regulatory trials in India. We have determined the sensitivity of the target lepidopterans to the insecticidal Bt proteins expressed in Bt maize, as this determines product efficacy and the resistance management strategy to be adopted. Maize hybrids with event MON89034 express two insecticidal Bt proteins, Cry1A.105 and Cry2Ab2. Sensitivity profiles of 53 populations of C. partellus, 21 populations of S. inferens and 21 populations of H. armigera, collected between 2008 and 2013 from maize-growing areas in India, to Cry1A.105 and Cry2Ab2 proteins were generated through dose-response assays. Cry1A.105 protein was the most effective to neonates of C. partellus (mean MIC90 range 0.30-1.0 µg mL(-1) ) and H. armigera (mean MIC90 range 0.71-8.22 µg mL(-1) ), whereas Cry2Ab2 (mean MIC90 range 0.65-1.70 µg mL(-1) ) was the most effective to S. inferens. Populations of C. partellus, S. inferens and H. armigera were susceptible to the Bt proteins Cry1A.105 and Cry2Ab2. The Bt sensitivity data will serve as precommercialisation benchmarks for resistance monitoring purposes.

Antixenosis and larval and adult dispersal in the Mediterranean corn borer, Sesamia nonagrioides, in relation to Bt maize

AbstractSesamia nonagrioides Lefèbvre (Lepidoptera: Noctuidae) is a key pest of maize [Zea mays L. (Poaceae)] and a main target of Bt maize in the Mediterranean area. To choose the most suitable non‐Bt refuge strategy for preventing or delaying resistance development in this maize borer, we examined its biology and behaviour. No antixenotic effects were found on numbers of eggs and egg batches per plant in choice (Bt vs. non‐Bt plants) and no‐choice assays. However, a greater ratio of young larvae dispersed from Bt than from non‐Bt plants. In addition, larvae that hatched on Bt plants tended to disperse more than those that hatched on non‐Bt plants, particularly during young growth stages. Many adults, especially females, could fly at least up to 400 m, as was found in a dispersal study with rubidium‐marked adults. The stimulation of larval dispersal by the Bt trait and the dispersal capacity of adults might compromise the efficacy of seed mixtures as an insecticide resistance management strategy.

New biological model to manage the impact of climate warming on maize corn borers

Climate change can modify the development of insect pests and their impact on crops. The study of future impacts on maize remains relatively unexplored. Here we modeled the distribution and development of the maize borer Sesamia nonagrioides Lef. in Europe using a 25 × 25 km grid. We studied the pest potential winter survival, distribution, and phenological development at three time horizons, 2000, 2030, and 2050, using the A1B scenario of the international panel on climate change (IPCC). A new model based on the lethal dose exposure concept was developed to simulate winter survival. Two approaches for the simulation of winter survival were compared: the first using air temperature only as weather input, named AirMS; the second taking into account the fraction of larvae overwintering in the soil, therefore considering also soil temperature, named SoilAirMS. The survival model was linked to a phenological model to simulate the potential development. Results show that soil temperature is an essential input for correctly simulating S. nonagrioides distribution. The SoilAirMS approach showed the best agreement (+537 grid cells), compared to the AirMS approach (−2,039 grid cells). Nevertheless, the AirMS approach allowed identifying areas where the agronomic practice suggested for controlling S. nonagrioides should be considered ineffective. This practice consists in uprooting and exposing the stubble on the soils surface for exposing larvae to winter cold. The projections to 2030 and 2050 suggested an overall slight increase of more suitable conditions for the S. nonagrioides in almost all the areas where it develops under the baseline. In these areas, S. nonagrioides could become a new insect pest with a potential strong impact on maize. This is the first attempt to provide extensive estimates on the effects of climate change on S. nonagrioides distribution, development, and on possible management changes.

Comparative study on the behavioral response and acute toxicity of some essential oil compounds and their binary mixtures to larvae of Helicoverpa armigera, Spodoptera litura and Chilo partellus

Comparative bioefficacy of five compounds in terms of acute toxicity and feeding and oviposition deterrence was determined against Helicoverpa armigera (Hübner), Spodoptera litura (F.) and Chilo partellus Swinhoe. Thymol was universally the most active compound, though with variable LD50 values depending upon the species evaluated. S. litura was the most susceptible with an LD50 of 28.5μg/larva followed by C. partellus with an LD50 of 189.7μg/larva and H. armigera with an LD50=290.8μg/larva. Comparative trend of acute toxicity, however, showed a significant overlap in activity for C. partellus and H. armigera when treated with various compounds. There was a reverse trend for feeding deterrence where H. armigera and S. litura gustatory response was similar in comparison to C. partellus, a specific maize borer that exhibits positive phototropism. Thymol and linalool were synergistically toxic against all the 3 species and carvacrol was antagonistic in all combinations. Response of S. litura was definitely different compared to the other 2 species. All the compounds deterred oviposition and were ovicidal too. Overall, thymol was the most active compound as an acute toxicant, oviposition deterrent, ovicide or a feeding deterrent against all the three insects. Other than thymol, 1,8-cineole and linalool were effective ovicidal compounds with an LC50=4.0 and 3.3mg/ml, respectively against H. armigera eggs but less active as oviposition deterrents than thymol; however, this deterrence was similar to the one observed in S. litura moths. 1,8-cineole and linalool were similar in deterring oviposition of C. partellus moths. Anethole was the least active as oviposition deterrent against all the 3 species evaluated and ODI50 values were 2.5–5-fold higher for this compound in both choice and no-choice situation.

Oviposition and feeding behavior of the maize borer, Chilo partellus, in response to eight essential oil allelochemicals

Eight essential oil compounds were evaluated against the maize borer, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae), to determine their influence on oviposition and feeding behavior. Thymol was the most active compound against C. partellus when evaluated as an oviposition deterrent (ODI 50 = 1.36 mg ml -1 ), an ovicide (LC 50 = 2.06 mg ml -1 ), or a feeding deterrent (FI 50 = 141.8 μg cm -2 ) in laboratory experiments. The results corroborated with greenhouse experiments, in which egg laying on maize plants was inhibited significantly when the treatment was 15 times the concentration used in the laboratory experiments. However, there was neither any correlation between oviposition deterrence and feeding inhibition, nor between oviposition deterrence and ovicidal action. Apparently, toxicity per se or ovicidal action does not play any role in choice of oviposition in C. partellus. This was more obvious when the efficacy of compounds was compared in greenhouse experiments where ODI values and number of eggs laid on the treated leaves did not differ significantly in choice and no-choice situations. Apparently, toxicity plays an important role in predicting host plant choice, but behavioral response in terms of oviposition preference is independent of toxic action, particularly for non-host toxins. Thus, the same compounds affecting oviposition behavior on the one hand and having ovicidal or feeding deterrent properties on the other could be useful in field situations in any area-wide integrated pest management model.

Evaluation of Dietary Toxicity of some Essential Oil Allelochemicals for The Management of Chilo Partellus (Swinhoe)

Eight essential oil compounds were used for study of larvicidal and growth inhibitory effects against the maize stem borer, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae). It is the most prevalent key pests, and is one of the limiting factors in the successful cultivation of the maize crop in India. Two dietary bioassays; on-diet and in-diet, were used. The bioassays showed different tenden- cies and LC 50 values were on the lower side in on-diet tests compared to in-diet assays. Thymol was the most active in both laboratory and greenhouse experiments. In greenhouse conditions, thymol was significantly active at a 10 x LC 50 level of treatment. Overall mor- tality due to thymol was 41.66% in 4 days and larvae failed to bore into the plant and could not feed until 48 h post-treatment. After 72 h there was some degree of feeding and boring in the plants by insects, but still < 45% of that in the controls. The present study suggests that larvicidal and growth inhibitory activity by the essential oil compounds could be beneficial as a possible control of the maize borer. This is especially true about thymol which has potential in field situations. It is effective if a proper delivery system and the appropriate time of sprays is established. A 4 day-interval spray of thymol against C. partellus can control the pest significantly and can be used in any integrated pest management system. On the basis of compound structure, no specific trend was observed.

Growth and development of Bacillus thuringiensis Cry1Ab‐susceptible and Cry1Ab‐resistant sugarcane borer on diet and conventional maize plants

AbstractThe sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), is a dominant maize borer pest and a major target of Bacillus thuringiensis (Bt)‐maize in Louisiana and the Gulf Coast area of Texas (USA). Growth and development of D. saccharalis on non‐toxic diet, diet treated with three low concentrations (0.01, 0.05, and 0.1 μg g−1) of Cry1Ab toxin, and on non‐Bt maize plants were compared for five insect genotypes: a Bt‐susceptible strain (BT‐SS), a Cry1Ab‐resistant strain (BT‐RR), a back‐crossed and re‐selected resistant strain (BT‐R’R’), and two F1 progeny of the BT‐SS and BT‐R’R’ strains. Fitness of the five genotypes was examined by infesting neonates on diet with/without Cry1Ab toxin in the laboratory and on intact non‐Bt maize plants in the greenhouse. Biological parameters measured were neonate‐to‐pupa development time and pupation rate, larval survival, larval and pupal weight, and sex ratio. Larvae of BT‐SS and BT‐R’R’ on non‐toxic diet and non‐Bt maize plants grew normally and there were no significant differences between the two strains in all measured parameters, suggesting a lack‐of‐fitness cost of the Cry1Ab resistance in D. saccharalis. Except for the development time on non‐Bt diet, all other parameters on both non‐Bt diet and non‐Bt maize plants were similar among the five genotypes. Larval development of BT‐SS was significantly affected on diet treated with Cry1Ab toxin at 0.05 and 0.1 μg g−1, whereas the effect to BT‐RR and BT‐R’R’ was not significant. Pupal weight and sex ratio reared on Cry1Ab‐diet were similar and there were no significant differences among the five genotypes. Neonate‐to‐pupation rate decreased as Cry1Ab concentrations increased but the decrease was more significant for BT‐SS than for the other four genotypes. The lack‐of‐fitness costs of Bt resistance in D. saccharalis imply a greater challenge in managing Bt resistance for this maize borer species.

Comparison of integrated field programmes for the reduction of fumonisin contamination in maize kernels

Fusarium verticillioides is a common maize pathogen which causes diseases on ears and synthesis of the mycotoxins, fumonisins, in kernels. Fumonisin production is influenced by both environmental conditions and agricultural inputs during growth and maturation of the maize plant. The aim of this research was to evaluate the effect of crop management techniques on fumonisin contamination in maize kernels. Experiments were conducted in Northern Italy during 2006 and 2007 using two maize hybrids with different precocity. Factors evaluated were seed planting time (March versus May), plant density (65,000 plants versus 80,000 plants per ha), N fertilization (200 kg N versus 400 kg N per ha), and chemical treatment to control European maize borer (ECB) (yes versus no). These factors were analyzed were as follows: (T1) May sowing, high plant density and N fertilization, (T2) March sowing time, high plant density and N fertilization, (T3) March sowing time, low plant density and balanced N fertilization, (T4) the same agronomic techniques as T3 plus a chemical treatment to control European maize borer. Ears were analyzed morphologically for ECB incidence and severity. Subsequently, kernels were analyzed chemically for fumonisins. Fumonisin contamination was reduced by 57%, 69% and 86% for T2, T3 and T4, respectively, compared to T1. This study clearly underlines that the application of good agricultural practices (GAP) in crop management strategies can effectively control fumonisin contamination of maize kernels.

Comparative activity of agrochemical treatments on mycotoxin levels with regard to corn borers and Fusarium mycoflora in maize ( Zea mays L.) fields

Field trials were carried out in nine areas located in France during 2004, 2005 and 2006 to study the control of Lepidoptera caterpillars by agrochemical treatments and their consequences on Fusarium spp. mycoflora and mycotoxin levels. Treatments involved either an insecticide or an insecticide–fungicide association. Two species of maize borers: Ostrinia nubilalis Hübner [Lepidoptera: Crambidae] and Sesamia nonagrioides Lefebvre [Lepidoptera: Noctuidae], were monitored. Although the insect populations were controlled by agrochemicals, there was no reduction in Fusarium spp. mycoflora. Conversely a significant reduction of mycotoxin (trichothecenes, fumonisins and zearalenone) levels resulted from insecticide treatment. These experiments and results are discussed regarding the biology of maize borers and relationships with Fusarium spp.