Effects of methyl jasmonate seed treatments on adult oviposition preference and larval performance of seed corn maggot (Delia platura) in corn (Zea mays).

BACKGROUND: Eliciting host plant resistance using plant hormones such as jasmonates has the potential to protect seeds and seedlings against insect pests; however, several hurdles exist for adapting it for pest management. This includes determining a dose that promotes resistance without limiting plant growth, an application method that growers could use, and ensuring the plants are responsive in the abiotic conditions when the pest occurs. In laboratory and field assays, we tested if treating corn seeds with multiple concentrations of methyl jasmonate would reduce the preference of ovipositing seed corn maggot adults and the performance of larvae feeding on seeds. RESULTS: We found that corn seeds soaked in aqueous 0.2 mM methyl jasmonate solution showed marginally lower seedling growth, but the adult oviposition preference was ~60% lower on these seeds compared to control water-soaked seeds. Seeds that were treated with methyl jasmonate using a conventional polymer-based seed coating showed no effect on seedling growth but reduced adult oviposition preference. In no-choice bioassays with adult flies, we found reduced oviposition on seeds soaked with aqueous methyl jasmonate compared to controls. Larval survival to pupation was also lower in methyl jasmonate-treated seeds. Lastly, the methyl jasmonate-induced resistance also occurred at the lower temperatures typical of the spring soil conditions when this fly is most damaging. CONCLUSION: Methyl jasmonate seed treatment in aqueous solution or using conventional polymer-based technology, has the potential to deter adult oviposition and reduce maggot performance in spring temperature conditions with minor effects on seed germination and growth. © 2024 Society of Chemical Industry.

Insights into How Spinosad Seed Treatment Protects Onion From Onion Maggot (Diptera: Anthomyiidae).

Onion maggot, Delia antiqua (Meigen), is a serious pest of onion Allium cepa L. in northern temperate regions. Over the last decade, D. antiqua has been managed principally using a pesticide seed treatment package containing the reduced-risk insecticide spinosad. While spinosad protects onion seedlings from D. antiqua, very little is known regarding how protection occurs. The main objectives of this study were to assess susceptibility of 1- and 2-wk-old larvae to spinosad through two different modes of exposure: ingestion and contact, and to evaluate larval feeding behavior in choice and no-choice tests with onion seedlings grown from treated and untreated seeds. Results showed that spinosad was more than twice as lethal to 1-wk than 2-wk-old larvae when it was ingested, but was equally toxic to both larval ages via contact exposure. In choice assays, larvae preferred feeding on untreated plants; however, without a choice, larvae fed and survived equally well on untreated and treated plants, suggesting that spinosad may have a deterrent effect. In a field study, levels of spinosad within young onion plants and in the soil around roots were monitored in addition to the cumulative number of onion seedlings killed by D. antiqua. Spinosad was detected in the soil and in both aboveground and belowground plant tissue, indicating that spinosad translocates into foliage, but declines in plant tissue and soil as plant mortality from D. antiqua feeding increases. Together, these results provide valuable insight into how spinosad protects onion seedlings and reveal key areas in need of further investigation.

Uptake and translocation of imidacloprid via seed pathway and root pathway during early seedling growth of corn.

BACKGROUND: A systemic seed treatment can be taken up into shoot tissues during early corn seedling growth. However, the pathway that a systemic compound is taken up, either from seed or root uptake to shoot tissues is not fully understood. To study the single contributions of seed pathway and root pathway for the uptake and translocation of imidacloprid seed treatment, two methods were developed: A seed treatment method and a growing media/hydroponic solution delivery method. The seed treatment method employed a live and dead seed separated with plastic wrap to provide a barrier. The growing media/hydroponic solution delivery method quantified the capacity for uptake by seeds and roots. RESULTS: The seed pathway transported 1.9-2.5 times more imidacloprid into shoot tissues when compared to the root pathway at the same dosage rate. The higher amount of imidacloprid taken up and translocated by the seed pathway was attributed to the fact that the corn seeds were in direct contact with high provided concentrations of imidacloprid. However, the root pathway showed 7.9-9.5 times higher capacity for transporting imidacloprid into shoot tissues when compared with the seed pathway. Whenever imidacloprid was taken up by seed or root, amounts of imidacloprid were measured in both tissues of seed and root. CONCLUSION: The seed pathway transported more imidacloprid than the root pathway during early seedling growth since corn seeds were contacted by higher concentrations of imidacloprid. Both seed pathway and root pathway were occurring concurrently during early seedling growth of corn. © 2020 Society of Chemical Industry.

Evaluation of Gelatin as a Biostimulant Seed Treatment to Improve Plant Performance.

The effect of gelatin, used as a biostimulant, was investigated on plant growth in greenhouse studies. Biostimulants are materials that stimulate plant growth, and gelatin, an animal protein hydrolysate, is classified as one type of biostimulant. Gelatin has a unique amino acid composition with a high percentage of proline and hydroxyproline. In a series of experiments gelatin capsules (#3 hard gelatin) containing 7.1 mg nitrogen each, were placed adjacent to seeds of different crop species, at sowing time in individual growing containers and several growth parameters were measured. Different types of hydrolyzed collagen, including granulated gelatin, gelatin hydrolysate, and amino acid mixtures simulating the composition of gelatin were compared on cucumber plant growth. In addition, amino acid mixtures without proline, hydroxyproline, or applied in combination were investigated on cucumber growth. All capsule treatments significantly enhanced crop growth compared to the non-treated control. The treatment with two gelatin capsules placed adjacent to each seed increased shoot dry weight of cucumber, pepper, broccoli, tomato, arugula, and field corn, by 138, 244, 50, 45, 41, and 18 percent, respectively. In an experiment with cucumber alone, there was a positive linear relationship between the number of gelatin capsules from 0 to 3 capsules on plant growth and plant nitrogen content. Cucumber growth and plant nitrogen content was greater from the hydrolyzed collagen treatment compared with the low molecular weight gelatin hydrolysate, a mixture of amino acids or urea and all treatments provided an equivalent amount of nitrogen. Proline and/or hydroxyproline were not responsible for the biostimulant effect. In summary, gelatin provided nitrogen that enhanced plant growth. Moreover, gelatin was an effective biostimulant as the plant growth and nitrogen content was greater from two gelatin capsules compared to amino acid mixture of the same proportion and amount as the gelatin.

Tomato Seed Coat Permeability to Selected Carbon Nanomaterials and Enhancement of Germination and Seedling Growth.

Seed coat permeability was examined using a model that tested the effects of soaking tomato (Solanum lycopersicon) seeds in combination with carbon-based nanomaterials (CBNMs) and ultrasonic irradiation (US). Penetration of seed coats to the embryo by CBNMs, as well as CBNMs effects on seed germination and seedling growth, was examined. Two CBNMs, C60(OH)20 (fullerol) and multiwalled nanotubes (MWNTs), were applied at 50 mg/L, and treatment exposure ranged from 0 to 60 minutes. Bright field, fluorescence, and electron microscopy and micro-Raman spectroscopy provided corroborating evidence that neither CBNM was able to penetrate the seed coat. The restriction of nanomaterial (NM) uptake was attributed to the semipermeable layer located at the innermost layer of the seed coat adjacent to the endosperm. Seed treatments using US at 30 or 60 minutes in the presence of MWNTs physically disrupted the seed coat; however, the integrity of the semipermeable layer was not impaired. The germination percentage and seedling length and weight were enhanced in the presence of MWNTs but were not altered by C60(OH)20. The combined exposure of seeds to NMs and US provided insight into the nanoparticle-seed interaction and may serve as a delivery system for enhancing seed germination and early seedling growth.

Evaluation of insecticides and application methods against Contarinia nasturtii (Diptera: Cecidomyiidae), a new invasive insect pest in the United States.

The midge Contarinia nasturtii (Keiffer), a serious gall-forming insect pest of cruciferous plants in Europe and southwestern Asia, was first reported in the United States in summer 2004. It had not been recorded in North America until its discovery in Ontario, Canada, in 2000. Efficacy of 20 insecticides belonging to 12 different classes was evaluated by using a foliar spray, soil drench, or seed treatment method. The broccoli cultivar 'Packman' was used in all tests at the suitable stage of four to five true leaves. Results indicated that foliar sprays of lambda-cyhalothrin, acephate, acetamiprid, chlorpyrifos, and methomyl reduced C. nasturtii larval populations by 96.7-100%. Except for acetamiprid, the other four insecticides also were effective against adults and provided 100% mortality after 24 h. When applied by drench, acetamiprid, imidacloprid, and thiamethoxam provided 100% control of C. nasturtii larvae, and the duration of efficacy lasted at least 7 wk. When applied as seed treatment, clothianidin and thiamethoxam provided 100% control of larvae and did not significantly affect seed germination. Imidacloprid also provided 100% control but the percentage of germination after treatment was only 62% (96.9% in check). These results indicate that several insecticides may significantly reduce midge populations. The nicotinoid class of insecticides, which has strong systemic activity, is likely to be the first choice. It is necessary to explore and develop other control methods such as cultural control and host resistance to develop an effective integrated pest management system.