Toxicity of synthetic piperonyl compounds to leaf-cutting ants and their symbiotic fungus

The Symbiotic Fungus Leucoagaricus gongylophorus (Möller) Singer (Agaricales, Agaricaceae) as a Target Organism to Control Leaf-Cutting Ants

Simple Summary

The most used approach to control leaf-cutting ants (which cause damage in agricultural areas) is the application of synthetic chemical compounds that directly affect these insects. But another approach is the use of natural substances that attack the symbiotic fungus responsible for many aspects of the survival of the nest. In this study, we discuss the natural substances already reported in the literature to have fungicidal activity and how they could be applicable as products for the control of leaf-cutting ants.

Abstract

Atta and Acromyrmex are the main genera of leaf-cutting ants present in North and South America, causing extensive damage to agroforestry. Control of the ants requires high handling costs with few effective methods available to decrease the losses. The symbiosis between the leaf-cutting ants and the fungus Leucoagaricus gongylophorus is essential for ant nest survival. Therefore, L. gongylophorus may be a key target in controlling leaf-cutting ants, since its reduction may cause an imbalance in the symbiosis necessary to maintain the nest. Among the options for natural fungal control, plant species are considered important sources of compounds belonging to several classes of natural products that show potential as antifungal agents. This review also presents studies that establish that the antagonist fungi from the Escovopsis and Trichoderma genera effectively reduce the development of L. gongylophorus. The development of nanostructured delivery systems, which have shown advantages over conventional formulations, is suggested for ant control; no commercial nanotechnology-based product has yet been developed, and this appears to be a new approach for future studies.

Lignans of Sesame (Sesamum indicum L.): A Comprehensive Review

Major lignans of sesame sesamin and sesamolin are benzodioxol--substituted furofurans. Sesamol, sesaminol, its epimers, and episesamin are transformation products found in processed products. Synthetic routes to all lignans are known but only sesamol is synthesized industrially. Biosynthesis of furofuran lignans begins with the dimerization of coniferyl alcohol, followed by the formation of dioxoles, oxidation, and glycosylation. Most genes of the lignan pathway in sesame have been identified but the inheritance of lignan content is poorly understood. Health-promoting properties make lignans attractive components of functional food. Lignans enhance the efficiency of insecticides and possess antifeedant activity, but their biological function in plants remains hypothetical. In this work, extensive literature including historical texts is reviewed, controversial issues are critically examined, and errors perpetuated in literature are corrected. The following aspects are covered: chemical properties and transformations of lignans; analysis, purification, and total synthesis; occurrence in Seseamum indicum and related plants; biosynthesis and genetics; biological activities; health-promoting properties; and biological functions. Finally, the improvement of lignan content in sesame seeds by breeding and biotechnology and the potential of hairy roots for manufacturing lignans in vitro are outlined.

Effect of sesame leaf diet on detoxification activities of insects with different feeding behavior

Three diverse insects, a polyphagous "leaf chewer" (Atractomorpha lata), a polyphagous "sap feeder" (Myzus persicae), and a "restrictive feeder" (Plutella xylostella) responded differently when fed with eight cultivars of sesame either as whole leaf or via artificial diet. There was limited or no correlation in induction between detoxifying enzyme substrates (esterase, glutathione s-transferase [GST], and mixed function oxidase [MFO] activities) when activity toward various substrates α-naphthyl acetate, 1-chloro-2,4-dinitrobenzene, 1,2-dichloro-4-nitrobenzene, and p-nitroanisole (pNA), were compared although they were generally elevated in the tissues from insects on sesame than a reference fed with radish seedlings. In A. lata, esterase activity for the cultivar 11Pusan and 45Laos were three-fold higher compared to the reference, while other cultivars, 24Nanbu-twasaki and 56S-radiatum were--two- to three-fold lower than the reference. In M. persicae, the esterase activity was as much as five-fold higher than the reference in one test cultivar. GST activities of the sesame cultivars were generally higher (≈two-fold) than the reference in all insects and at variable ratios among the cultivars. The MFO activity toward pNA in grasshoppers feeding on these sesame cultivars was either highly expressed or nonexistent. These results indicate that although the cultivars belong to the same species, they might have undergone changes in secondary phytochemicals in response to varying biogeographical distribution. Each insect species is suspected to target a specific plant chemical burden that it tries to overcome in each cultivar through enzyme activation.

Acromyrmex octospinosus (Hymenoptera: Formicidae) management. Part 1: Effects of TRAMIL's insecticidal plant extracts

BACKGROUND

Leaf-cutting ants are considered to be one of the most important pest species of the New World. Until now, control strategies against these leaf-cutting ants have mainly been synthetic chemicals. The aim of the present study was to test the action of several plant extracts quoted as an example by TRAMIL participative surveys for their insecticidal properties on adult major workers of Acromyrmex octospinosus. Three tests were used to that end: contact toxicity, repellent test and ingestion bioassay. Six traditional plant uses recommended by interviewed people in surveys were tested: (1) maceration of Mammea americana fresh crushed seeds; (2) decoction of Nerium oleander fresh leaves; (3) Nerium oleander dried leaf water juice; (4) decoction of Nicotiana tabacum dried leaves; (5) Trichillia pallida dried leaf water juice; (6) decoction of Rollinia mucosa dried seeds.

RESULTS

Two plant extracts with contact toxicity (Mammea americana and Nicotiana tabacum), six plant extracts with repellent activity and four plant extracts with ingestion toxicity (Mammea americana, Nicotiana tabacum and both extracts of Nerium oleander) were found.

CONCLUSION

The data presented in this study showed that plant extracts cited by TRAMIL ethnopharmacological surveys have the potential to control the leaf-cutting ant, Acromyrmex octospinosus. In particular, the Mammea americana extract, with its natural low repellent effect and its high toxicity by ingestion, and Nerium oleander extracts, with their natural delay action, are possibly the best extracts for the control of these ants.

Relationship between metabolic and genomic diversity in sesame (Sesamum indicum L.)

Background

Diversity estimates in cultivated plants provide a rationale for conservation strategies and support the selection of starting material for breeding programs. Diversity measures applied to crops usually have been limited to the assessment of genome polymorphism at the DNA level. Occasionally, selected morphological features are recorded and the content of key chemical constituents determined, but unbiased and comprehensive chemical phenotypes have not been included systematically in diversity surveys. Our objective in this study was to assess metabolic diversity in sesame by nontargeted metabolic profiling and elucidate the relationship between metabolic and genome diversity in this crop.

Results

Ten sesame accessions were selected that represent most of the genome diversity of sesame grown in India, Western Asia, Sudan and Venezuela based on previous AFLP studies. Ethanolic seed extracts were separated by HPLC, metabolites were ionized by positive and negative electrospray and ions were detected with an ion trap mass spectrometer in full-scan mode for m/z from 50 to 1000. Genome diversity was determined by Amplified Fragment Length Polymorphism (AFLP) using eight primer pair combinations. The relationship between biodiversity at the genome and at the metabolome levels was assessed by correlation analysis and multivariate statistics.

Conclusion

Patterns of diversity at the genomic and metabolic levels differed, indicating that selection played a significant role in the evolution of metabolic diversity in sesame. This result implies that when used for the selection of genotypes in breeding and conservation, diversity assessment based on neutral DNA markers should be complemented with metabolic profiles. We hypothesize that this applies to all crops with a long history of domestication that possess commercially relevant traits affected by chemical phenotypes.