Toxicity and behavioural effects of diet-borne alkaloids on larvae of the black blowfly, Phormia regina.

Larvae of the black blowfly, Phormia regina (Meigen) (Diptera: Calliphoridae) were exposed for 24 h to artificial diets that contained one of the following alkaloids: arecoline, caffeine, nicotine, quinine, sparteine or strychnine at either 1000 or 100 p.p.m. Each of the alkaloids caused reduced weight gain, relative to a control population in a no-choice bioassay and, with the exception of quinine, all alkaloids caused reduced larval weights in a choice bioassay. Larvae were unable to move away from diets containing arecoline (1000 and 100 p.p.m) and congregated away from diets containing 1000 p.p.m. quinine. Arecoline (1000 p.p.m) and both concentrations of nicotine caused significant mortality of larvae. Over a longer period (120 h), 10 and 1 p.p.m. nicotine resulted in significant numbers of larvae congregating away from a treated diet. Ten p.p.m. nicotine caused reduced weight gain over 120 h, although larvae provided with a choice were less affected. Exposure of larvae to dried residues of nicotine for 2 h did not affect subsequent development.

Responses of Spodoptera littoralis larvae to Tunisian plant extracts and to neo-clerodane diterpenoids isolated from Ajuga pseudoiva leaves.

Thirteen plants growing in Tunisia were tested against Spodoptera littoralis larvae. From the acetone extract of Ajuga pseudoiva leaves, showing interesting antifeedant activity, three new (1-3) and two known (4-5) active clerodane diterpenoids were isolated following a bioassay-guided chromatography.

Bioactive sesquiterpenes from Santolina rosmarinifolia subsp. Canescens. A conformational analysis of the germacrane ring.

The hexane extract of aerial parts of Santolina rosmarinifolia subsp. canescens afforded eight new sesquiterpenes in addition to known compounds. Their structures were determined by spectroscopic methods and chemical transformations. The conformational analysis of the germacrane constituents was carried out by spectroscopic methods, including NMR at varying temperature and by molecular mechanics calculations. The antifeedant, antibacterial and antitumoral activity of selected compounds has been tested.

From a phagostimulant natural product to semisynthetic antifeedants against Spodoptera littoralis larvae: chemical transformations of the neoclerodane diterpenoid scutegalin B.

Scutegalin B (4), a natural neoclerodane diterpenoid possessing phagostimulant activity against larvae of the lepidopteran Spodoptera littoralis, has been subjected to a series of chemical transformations obtaining several derivatives. The activity of some of these changes to antifeedant (10, 12, 16, and 17), although other derivatives are inactive (6, 7, and 15) or maintain phagostimulant activity (8 and 9) of the starting material (4). The most potent antifeedant was 16, which possesses 16,15-lactone and a (19S)-19, 2alpha-hemiacetal groups instead of the 16,15-lactol and (19R)-(19-O-tigloyl)19,2alpha-hemiacetal of the phagostimulant precursor 4. These and other structure-activity relationships are discussed, establishing that the biological action is strongly modulated by minimal structural variations.

Developmental inhibition ofSpodoptera litura (Fab.) larvae by a novel caffeoylquinic acid from the wild groundnut,Arachis paraguariensis (Chod et Hassl.).

A novel compound, 1-caffeoyl-4-deoxyquinic acid (1-CdQA) has been identified along with 3-caffeoylquinic acid (3-CQA) and 5-caffeoylquinic acid (5-CQA) (syn. chlorogenic acid) in the foliage ofArachis paraguariensis, a wild species of groundnut that is highly resistant to attack by the larvae ofSpodoptera litura. When neonate larvae were fed on diets treated with 3-CQA or 1-CdQA, their development was severely inhibited compared to larvae on untreated diets, and the effects were similar in nature and magnitude to those observed for larvae feeding on diets treated with 5-CQA, rutin, and quercetin. The effects of all the compounds were dose related, and their optimal concentration was approximately 3 mM, which corresponds to the total foliar concentration of both caffeoylquinic acids and quercetin diglycosides inA. paraguariensis. After 24 h, the development of third stadium larvae feeding on diets treated with 5-CQA, rutin and 1-CdQA was promoted compared to larvae on control diets, but after 96 hr larvae feeding on treated diets had gained significantly less weight than those on the control diets. 1-CdQA, 3-CQA, and quercetin dyglycosides (previously identified in the foliage ofA. paraguariensis) are considered to be valuable components in resistance of groundnuts toS. litura and may provide useful genetic markers in future breeding for resistance to this pest.

Variation in chemosensitivity and the control of dietary selection behaviour in the locust.

Investigations into the behavioural and underlying physiological mechanisms of dietary selection are presented for the locust, Locusta migratoria. Locusts were fed for 4, 8 or 12 h on one of four chemically defined artificial diets: diet PC, which was nutritionally complete; diet P, containing no digestible carbohydrate; diet C, containing no protein; and diet O, which lacked both protein and digestible carbohydrate. Following this pretreatment, the locusts were provided with both the P and the C diet in a choice test. Detailed analyses of selection behaviour indicated that diets lacking a nutrient for which the insect was deficient were either rejected before a meal was initiated, or, if feeding commenced, eaten in meals of only short duration, while those containing the appropriate nutrients were accepted more readily and eaten in longer meals. Electrophysiological studies showed that this behaviour was paralleled by nutrient-specific changes in gustatory responsiveness. Locusts pretreated for 4h on C diet had increased gustatory responsiveness to stimulation with an amino acid mix, but not to sucrose, while insects fed on P diet showed increased responsiveness to stimulation with sucrose, but not to the amino acid mix. This result is consistent with earlier experiments in which levels of blood nutrients were shown to modulate taste responsiveness in the locust.

Behavioral and electrophysiological study of antifeedant mechanisms associated with polyhydroxy alkaloids.

Eleven polyhydroxy alkaloids of plant origin were tested for anti-feedant effects against larvae of the lepidopteransSpodoptera littoralis, Spodoptera frugiperda, Heliothis virescens, andHelicoverpa armigera. Data from behavioral and electrophysiological investigations were correlated to reveal information on the mode of action of the antifeedants. The pyrrolidine DMDP was an effective antifeedant for all four species, whereas the piperidines fagomine and XZ-1 and the pyrrolizidine alexine were all ineffective as antifeedants. The activity of the pyrrolidines CYB-3 and DAB-1, the piperidines DNJ, DMJ, and BR1, and the bicyclic octahydroindolizine castanospermine varied among species. The investigation focuses on the structural similarities between some of the alkaloids and some common phagostimulatory sugars and illustrates a neural interaction involving the neurons that are differentially responsive to alkaloids and sugars. InS. littoralis, the neurons responding specifically to the alkaloids DMDP, DAB-1, and castanospermine and to the sugars fructose, sucrose, and glucose are more active when the compounds are applied singly than when an alkaloid and a sugar are applied together. The implications for the occurrence and functioning of different sugar receptor sites are discussed.

Insect antifeedant activity associated with compounds isolated from species ofLonchocarpus andTephrosia.

The antifeedant activity of a series of 21 chalcones, flavanes, and flavanones isolated from the generaLonchocarpus andTephrosia (Leguminosae) was assessed by behavioral and electrophysiological bioassays against larvae ofSpodoptera littoralis andS. exempta. The antifeedant activity is related to the molecular structure of the compounds, and possible modes of interaction with the insect taste receptors are discussed.

Insect antifeedant properties of anthranoids from the genusVismia.

Vismiones and ferruginins, representatives of a new class of lypophilic anthranoids from the genusVismia were found to inhibit feeding in larvae of species ofSpodoptera, Heliothis, and inLocusta migratoria.

The ultrastructure of an olfactory sensillum on the maxillary palps of locusta migratoria (L.).

The olfactory sensilla on the maxillary palp tip of Locusta migratoria (L.) resemble the surrounding contact chemoreceptors in general morphology. The perforated peg has a thicker wall than is commonly found in olfactory sensilla. The form and position of the sensilla are considered in relation of the olfactory function. The fine structure of the dendrites is discussed in relation to that described in other olfactory sensilla.

The significance of palpation by the maxillary palps of Locusta migratoria (L): an electrophysiological and behavioural study.

Palpation increases the amount of sensory input reaching the central nervous system compared with that obtained from sustained contact but that increase is not essential to allow discrimination. During a meal on favoured food, phagostimulatory input from the palps is not needed to drive feeding. When less favoured food is taken, phagostimulatory input from the palps may enhance feeding. Even with favoured food, the palps are important in registering inhibitory substances.

Behavioural and electrophysiological studies of taste discrimination by the maxillary palps of larvae of Locusta migratoria (L.).

1. Behavioural studies show that larvae of Locusta migratoria (L.) can discriminate between certain simple chemicals and between chemicals obtained from plant sources. 2. Electrophysiological tests show that within each sensillum the same neurones respond to different chemicals. 3. The frequency of occurrence of sensilla with enhanced specificity to certain chemicals is investigated. 4. Statistical tests confirm that, despite the variability of response, across-fibre analysis could allow discrimination between chemicals provided an adequate number of senilla are used. 5. The conclusions are discussed in relation to current theories of chemoreceptor functioning.