James A. Klocke

1,8-Cineole (Eucalyptol), a mosquito feeding and ovipositional repellent from volatile oil ofHemizonia fitchii (Asteraceae).

The mosquito feeding and ovipositional repellency of the major monoterpenoid present in the volatile oil ofHemizonia fitchii (Asteraceae), i.e., 1,8-cineole, was investigated. Although 1,8-cineole did not exhibit any significant mosquito larvicidal activity, it was moderately effective as a feeding repellent and highly effective as an ovipositional repellent against adultAedes aegypti (yellow fever mosquito). The ovipositional repellency of 1,8-cineole, coupled with the presence of severalHemizonia chromenes previously shown to possess mosquito larvicidal activity, may therefore account in large part for the observed suppression of local mosquito populations which was associated withH. fitchii plants in northern California.

Effects of azadirachtin on the nutrition and development of the tobacco budworm, Heliothis virescens (Fabr.) (Noctuidae)

Abstract The plant chemical azadirachtin was administered, either in artificial diet or by oral injection, to fifth instar larvae of the tobacco budworm, Heliothis virescens (Fabr.). At a dietary concentration of 0.03125 ppm, azadirachtin significantly reduced the amount of diet consumed and the weight gained by the larvae. Higher dietary concentrations (0.25 and 0.5 ppm) were necessary to reduce the efficiency of larval conversion of digested and ingested food, respectively. However, the approximate digestibility increased at the dietary concentration of 0.25 ppm. Orally injected azadirachtin (0.25 and 0.5 μg) delayed moulting to the pupal stage, produced defective pupae or adults, and inhibited development to the adult stage. Higher doses (5.0 and 10.0 μg) reduced the pre-pupal weight loss normally associated with pupation, and completely inhibited pupation. At the critical dose of 1.0 μg (the minimal dose that disrupted development to the pupal stage), azadirachtin had less of an effect on older than on younger larvae. Larvae injected on the first day of the fifth instar failed to pupate, whereas approx 40% of those injected on subsequent days pupated. The results suggest that azadirachtin affects H. virescens in a manner similar to other tested species of insects. The significance of these results, especially regarding hormonal events in the insects, is discussed.

Citrus limonoid by-products as insect control agents

Limonoids are a group of chemically related bitter tetranortriterpene derivatives found predominantly in Rutaceae and Meliaceae plants (Ourison et al., 1964). Interest in the Rutaceae limonoids has centered around limonoid removal from consumable citrus products. For example, bitterness in citrus juices (as well as in other citrus products) due to limonoids has become an increasingly serious economic problem (Wilson & Crutchfield, 1968; Sinclair, 1972). Interest in the Meliaceae limonoids, on the other hand, has centered on their efficacy as pest control and/or antitumor agents (Kubo & Klocke, 1981, 1982; Nakanishi, 1977, 1980). For example, azadirachtin, isolated from several Meliaceae trees, has proven to be a potent natural product against a myriad of insect and nematode pests (Warthen, 1979). In fact, we have isolated azadirachtin from the fresh fruit of Azadirachta indica as a potent insect ecdysis inhibitor against four agricultural pest insects with artificial diet feeding assay (Kubo & Klocke, in litt).

New insect ecdysis inhibitory limonoid deacetylazadirachtinol isolated from azadirachta indica (meliaceae) oil

Abstract Insect bioassay-guided fractionation of neem oil expressed from the fresh fruits of Azadirachta indica (Meliaceae) resulted in the isolation and structural elucidation of a new limonoid, deacetylazadirachtinol ( 1 ). In addition, four previously elucidated limonoids, including azadirachtin ( 2 ), salannin( 3 ), 6- 0 -acetylnimbandiol ( 4 ), and 3-desacetylsalannin ( 5 ), were isolated from the same source, spectrally identified, and bioassayed. The structure of 1 was elucidated by spectral comparison with the known azadirachtin using their 1H-1H and 1H-13C 2D NMR spectra to assign the total 1H and 13C chemical shifts. Deacetylazadirachtinol was found to be as potent as azadirachtin in the inhibition of insect ecdysis when fed in artificial diet to larvae of the tobacco budworm. Heliothis virescens (Noctuidae). The other isolated limonoids were much less active against H. virescens .

Effects of azadirachtin on levels of ecdysteroids and prothoracicotropic hormone-like activity in Heliothis virescens (Fabr.) larvae

Abstract Oral injections of 1 μg of the plant chemical azadirachtin into final (fifth)-instar larvae of the tobacco budworm, Heliothis virescens (Fabr.), reduced whole body and haemolymph titres of the moulting hormones, ecdysone and 20-hydroxyecdysone, below those of control larvae, thereby preventing normal development to the pupal stage. Likewise, oral injections of 1 μg of azadirachtin reduced brain levels of prothoracicotropic hormone (PTTH)-like activity, which is the stimulation of in vitro moulting hormone synthesis by the prothoracic glands. In addition, prothoracic glands from azadirachtin-treated larvae were less receptive to stimulation in vitro and in vivo by control brain extracts of PTTH compared to control glands. However, azadirachtin did not directly inhibit the in vitro synthesis of moulting hormone when the compound was included in the incubation media with prothoracic glands from control larvae. A timely haemocoel injection of 20-hydroxyecdysone into azadirachtin-treated larvae resulted in partial recovery of development to the pupal stage. Based upon these data, we suggest that in preventing normal development of final-instar larvae of H. virescens, azadirachtin reduces moulting hormone titres by reducing PTTH titres and the receptivity of prothoracic glands to produce ecdysone via stimulation by PTTH.

The ellagitannin geraniin and its hydrolysis products isolated as insect growth inhibitors from semi-arid land plants.

Abstract The phenolic dilactone, ellagic acid, was isolated and identified from the hot methanolic extracts of five species of semi-arid land plants as an insect growth inhibitor active against the polyphagous herbivore, Heliothis virescens (tobacco budworm). Ellagic acid bound as its hexahydroxydiphenoyl ester in the ellagitannin, geraniin, also was isolated (using milder extraction procedures) and spectrally identified from one of the five species (i.e. Geranium viscosissimum var. viscosissimum) as a growth inhibitor of H. virescens. Evidence is given for the hypothesis that the labile geraniin is a protoxin which releases insect growth inhibitors, particularly ellagic acid, upon hydrolytic cleavage. The free and bound forms of ellagic acid may explain the insect growth inhibitory activity detected in the methanolic extracts of many species in the Hamamelididae-Dilleniidae stock.

The structure of 1-cinnamoylmelianolone, a new insecticidaltetranortriterpenoid, from Melia Azedarach L. (Meliaceae)

Abstract 1-Cinnamoylmelianolone ( 1 ), a new insecticidal tetranortriterpenoid, was isolated from methanolic extracts of the fruit of Melia azedarach L. The structure of 1 is proposed on the basis of spectral data.

7-Deacetyl-17β-hydroxyazadiradione, a new limonoid insect growth inhibitor from Azadirachta indica

Abstract A new tetranortriterpenoid of the limonoid type, 7-deacetyl-17β-hydroxyazadiradione, and the known compound azadiradione, were isolated from the seeds of Azadirachta indica . The structure of the new compound was established by spectroscopic methods. The activity of the new compound as an insect growth inhibitor against Heliothis virescens was found to be greater than that of azadiradione and 7-deacetylazadiradione.

Symposium: Insect Behavioral Ecology--'90: Defense of Plants Through Regulation of Insect Feeding Behavior

Feeding deterrents, or antifeedants, are chemicals that can protect plants from insect herbivory through regulation of insect feeding. The sensitivity of a given species of an insect herbivore is dependent upon the quantity and chemical structure of the feeding deterrent. Feeding deterrency can be caused by an effect of the chemical on chemoreception and/or on the centers that regulate feeding and metabolism. Feeding deterrents primarily affect the feeding behavior of insects, but often they are also toxic if fed upon. Examples of feeding deterrents that play an important role in the multichemical defense of plants from insects are azadirachtin isolated from Azadirachta indica (Meliaceae) and rhodojaponin III isolated from Rhododendron molle (Ericaceae). These two terpenoidal plant products, so effective in nature, are currently being tested for use in commercial insect control.

Structure of ajugarin-IV

The structure of a new neo-clerodane diterpene, ajugarin-IV, isolated from Ajuga remota and possessing insecticidal activity, has been established by means of spectroscopic and chemical data.