Novel Agmatine Derivatives in Maerua edulis With Bioactivity Against Callosobruchus maculatus, a Cosmopolitan Storage Insect Pest.

Food security in developing countries is threatened by crop pests and ectoparasites in livestock. Strategies for their management still rely on synthetic pesticides which are not always effective and the active ingredients persist in the environment with negative consequences for beneficial arthropods, farmers and consumers, hence necessitating research on sustainable alternatives. Botanical insecticides are increasingly relevant, typically having lower impacts on users, consumers and the environment. One example is the southern African shrub the Blue bush-berry, Maerua edulis. Recent work reported effective pest control using this plant species against cattle ticks, storage beetles and vegetable pests. However, little is known about the chemistry underlying activity and this is essential to optimize its use. Here, we identified two novel plant chemical structures, the E and Z isomers of cinnamoyl-4-aminobutylguanidine along with the E and Z isomers of 4-hydroxycinnamoyl-4-aminobutylguanidine in the leaves of M. edulis. We isolated these compounds from the leaves and elucidated their chemical structures using various spectroscopic techniques including High Resolution Mass Spectrometry and Nuclear Magnetic Resonance Spectroscopy. We also identified a further 11 closely related structures of which 6 are tentatively reported here for the first time. Stachydrine and 3-hydroxystachydrine were also identified in the leaf extract, and occurred at very high concentrations; up to 2% w/w of dry leaves. We tested these two compounds, along with the 4 main cinnamoylamides and the crude M. edulis leaf extract against the cowpea bruchid Callosobruchus maculatus at concentrations equivalent to those present in extracts used by smallholder farmers. Mortality of insects exposed to crude plant extracts after 72 h was significantly higher than the untreated control although still lower than for insects exposed to rotenone, the positive control. The two new compounds and stachydrine showed similar activity to the crude extracts suggesting that these compounds explained the activity of the extract. After 6 days, the mortality of insects exposed to crude extracts and isolated compounds was similar to that recorded with the positive control. The stachydrine fraction and the E and Z isomers of cinnamoyl-4-aminobutylguanidine also inhibited oviposition activity in fecund female beetles. Our data show that methanol extracts of M. edulis were toxic to C. maculatus and inhibited oviposition even at 0.1% w/v so these foliar chemicals may explain the activity of the plant material. We also synthesized the amides which facilitated structural elucidation, produced adequate quantities for testing and demonstrated the potential for commercial synthesis.

Nor-hopanes from Zanha africana root bark with toxicity to bruchid beetles.

Zanha africana (Radlk.) Exell (Sapindaceae) root bark is used by farmers throughout sub-Saharan Africa to protect stored grain from bruchid beetles, such as Callosobruchus maculatus. Chloroform, methanol and water extracts of Z. africana root bark inhibited oviposition and caused significantly higher mortality of C. maculatus at a rate of application equivalent to that applied by farmers compared to control insects. The chloroform extract contained nor-hopanes rarely found in plants of which seven were isolated, one of which was previously known. Two of the most abundant nor-hopanes 3ß,6ß-dihydroxy-7ß-[(4-hydroxybenzoyl)oxy]-21αH-24-norhopa-4(23),22(29)-diene and 3ß,6ß-dihydroxy-7ß-[(4-hydroxybenzoyl)oxy]-24-norhopa-4(23),17(21)-diene were toxic to and reduced oviposition of C. maculatus in a dose dependent manner. Z. africana root bark is rich in insecticidal compounds that account for its effective use by smallholder farmers as an alternative to conventional insecticides.

Can Coffee Chemical Compounds and Insecticidal Plants Be Harnessed for Control of Major Coffee Pests?

Pests and pathogens threaten coffee production worldwide and are difficult to control using conventional methods, such as insecticides. We review the literature on the chemistry of coffee, concentrating on compounds most commonly reported from Coffea arabica and Coffea canephora. Differences in chemistry can distinguish coffee species and varieties, and plants grown under different biogeographic conditions exhibit different chemotypes. A number of chemical groups, such as alkaloids and caffeoylquinic acids, are known to be insecticidal, but most studies have investigated their effects on coffee quality and flavor. More research is required to bridge this gap in knowledge, so that coffee can be bred to be more resistant to pests. Furthermore, we report on some pesticidal plants that have been used for control of coffee pests. Locally sourced pesticidal plants have been underutilized and offer a sustainable alternative to conventional insecticides and could be used to augment breeding for resilience of coffee plants.

The scope for using the volatile profiles of Pinus caribaea var. bahamensis as indicators of susceptibility to pine tortoise scale and as predictors of environmental stresses.

Climate change, unseasonal fire and urbanization are contributing to the decline of Pinus caribaea var. bahamensis populations in the Turks and Caicos Islands (TCI). Infestation of pines with the invasive pine tortoise scale (PTS, Toumeyella parvicornis) is accelerating this decline. Pine trees in the Bahamas are larger and healthier and are not infested with PTS although they are subject to some of the same environmental pressures as the trees in TCI. Volatile compounds were collected from wild and nursery-reared P. caribaea var. bahamensis from TCI and the Bahamas and characterized using GC/MS analysis, to look for differences between the compounds detected in insect-infested pines of TCI and the healthy pines of the Bahamas. Ten compounds contributing at least 1% of the total detected peak areas in any one of the samples were selected for further study. Eight of these compounds were identified using authentic standards and mass spectral libraries. The main constituents in the samples were α- and ß-pinene as well as ß-phellandrene, and, together with ß-myrcene, their contents varied the most between samples collected at different locations. Principal-component analysis showed that the two structural isomers of pinene, together with ß-myrcene and ß-phellandrene, contributed 98.4% of the variance between samples. There was a positive relationship between the concentrations of the two structural isomers of pinene and between levels of ß-myrcene and ß-phellandrene. The results are discussed in relation to the biology and adaptations of invasive scale insects, the importance of monoterpenes in pine as a defense against insect predation, whether these compounds can be used as indicators of tree health, and future directions for research into conserving the Caicos pine.

Dalnigrin, a neoflavonoid marker for the identification of Brazilian rosewood (Dalbergia nigra) in CITES enforcement.

International trade in Brazilian rosewood, Dalbergia nigra (Vell.) Allemão ex Benth., is regulated by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). One problem in enforcing these regulations is the difficulty in distinguishing the wood of D. nigra from that of a closely-related but unregulated species, Dalbergia spruceana Benth. Using LC-MS to analyse methanol extracts of xylaria specimens, we identified a chemical marker for D. nigra heartwood, and determined its structure as the neoflavonoid 6-hydroxy-7-methoxy-4-(4-methoxyphenyl)-2H-1-benzopyran-2-one (4'-O-methylmelanettin; dalnigrin), using spectroscopic techniques. Dalnigrin was present in all nine available heartwood specimens of D. nigra, but it was not detected in extracts of 59 other heartwood samples representing 15 species of Dalbergia, including D. spruceana. Five other phenolic compounds were also isolated from D. nigra heartwood and similarly identified as the neoflavonoids 3'-hydroxymelanettin, melanettin, melannein and dalbergin, and the isoflavone caviunin. In extracts of D. spruceana heartwood, pseudobaptigenin was identified by LC-MS to be a major phenolic component that was not detected in wood extracts of D. nigra. We conclude that chemical analysis, in combination with anatomical investigation, can provide persuasive evidence to support the positive identification of untreated heartwood of D. nigra.

The effects of insect extracts and some insect-derived compounds on the settling behavior of Liposcelis bostrychophila.

Extracts of whole booklice (Liposcelis bostrychophila)-sequentially extracted in hexane and aqueous 80% methanol (80%MeOH)-repel conspecifics. A methanol-soluble fraction (MFr) of the 80% methanol extract was more repellent than either its corresponding water fraction (WFr) or the hexane extract. The repellent effect of the MFr was repeatable across extracts prepared on different occasions over a 1 month period. Gas chromatography, mass-spectrometry (GC-MS) analyses showed that saturated (C(16); C(18)) monoenoic (C(16:1); C(18:1)) and a dienoic fatty acid (C(18:2)) and the corresponding methyl esters of all but C(16:1) and C(18) constituted approximately 95% and 30%, of the detected compounds in the methanol fractions and the hexane extract, respectively. Qualitative thin layer chromatography showed that cholesterol was present in methanol fractions and the hexane extract, and also enabled tentative identification of triacylglycerols and phospholipids in the methanol fractions. Extracts of wheatgerm, dried skimmed milk powder, active yeast, and wholemeal flour-L. bostrychophila dietary components-were analyzed by GC-MS, and C(16), C(18:1) and C(18:2) were detected, indicating that C(18) and the methyl esters were not directly extractable and/or that they were products of booklice metabolism. A fatty acid amide (stearamide) previously identified in cuticular extracts of L. bostrychophila was not detected, and therefore was not responsible for the observed biological activity. Pure fatty acids and fatty acid methyl esters repelled settling of L. bostrychophila at 10 mM, with the exception of palmitic and stearic acids, indicating, among other things, a difference between the efficacy of saturated and unsaturated fatty acids. The effect of concentrations <10 mM was less significant, although palmiteoleic acid appeared to be attractive to L. bostrychophila at 0.1 mM. Fatty acids and fatty acid methyl esters were at a much lower concentration than 10 mM in the repellent methanol fractions, indicating that an interaction between known and as yet unidentified compounds is likely. The significance of fatty acids in relation to the biology and behavior of L. bostrychophila and their potential for use in traps and monitoring are discussed.

Effects of plant-derived compounds on larvae of a blow fly species that causes secondary myiases: laboratory studies.

No-choice and binary-choice bioassays were used to test the effect of a range of plant-derived insecticides on the behaviour of larvae of the black blow fly Phormia regina (Meigen). Azadirachtin (100 and 10 ppm), pyrethrum extract (10 ppm) and the naphthoquinone BTG 505 (1000 ppm) acted as deterrents for P. regina larvae. The mortality of larvae was reduced in instances where they moved away from a treated diet. Larvae given a choice were heavier, when compared with larvae reared exclusively on diets containing either azadirachtin (100 or 10 ppm) or the naphthoquinones, BTG 504 (1000 ppm) or BTG 505 (1000 ppm). The deterrent effect of azadirachtin, pyrethrum and the naphthoquinone BTG 505 together with their larvicidal activity, could be utilized in prophylaxis against myiasis infections due to larvae of Phormia regina.

Phenolic compounds on the pod-surface of pigeonpea, Cajanus cajan, mediate feeding behavior of Helicoverpa armigera larvae.

A methanol extract of the pod surfaces of Cajanus cajan, a feeding stimulant for fifth-instar Helicoverpa armigera, was shown to contain four main phenolic compounds. Three of these were identified as isoquercitrin, quercetin, and quercetin-3-methyl ether, by comparing UV spectra and HPLC retention times with authentic standards. The fourth compound was isolated by semipreparative HPLC and determined to be 3-hydroxy-4-prenyl-5-methoxystilbene-2-carboxylic acid (stilbene) by NMR spectroscopy and mass spectrometry. Quercetin, isoquercitrin, and quercetin-3-methyl did not affect the selection-behavior of fifth-instar H. armigera. However, larvae were deterred from feeding on glass-fiber disks impregnated with the stilbene. Furthermore, larvae exposed to quercetin-3-methyl ether consumed significant amounts of both disks. In a binary-choice bioassay, a combination of quercetin-3-methyl ether and the stilbene on one disk and pure quercetin-3-methyl ether on the other disk resulted in increased consumption of both glass-fiber disks by larvae. In contrast, consumption was reduced if the combination was presented to larvae on one disk with purified stilbene on the other disk. Cajanus cajan cultivars that varied in their susceptibility to H. armigera were surveyed forthe presence of the four phenolic compounds. An absence of quercetin and higher concentrations of isoquercitrin than the cultivated variety characterized pod surface extracts of pod-borer-resistant cultivars. In addition, the ratio of the stilbene to quercetin-3-methyl ether was greater in the pod-borer-resistant cultivars. These findings are discussed in relation to the identification of chemical characters that can be used for crop improvement.