A. Randall Alford

Effects and modes of action of citrus limonoids against Leptinotarsa decemlineata

ABSTRACT Limonin and its five derivatives were evaluated in feeding bioassays for depression effects on feeding, growth and development of the fourth stadium Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae). Epilimonol and limonin diosphenol were most effective in depression of feeding and growth, with ED50s 10 and 8 μg/cm2. At a dosage of 31.6 μg/cm2, epilimonol, limonin diosphenol and limonin caused both significant feeding reduction and developmental delay, while deoxylimonol, tetrahydrolimonin and limonol were not effective. Mouth‐part coating and antifeedant bioassays show that feeding inhibition at host acceptance level seems to be the primary mode of action of epilimonol and limonin diosphenol.

Triterpenes from the Outer Bark of Betula nigra

Abstract Twelve pentacyclic triterpenes were isolated from the outer bark of river birch, Betula nigra. 3β-Acetoxyolean-11-oxo-12-ene-28-oic acid was isolated for the first time from a Betula species. 3β-Caffeatoxyolean-12-ene-28-oic acid has been spectrally characterized for the first time. 3β-Acetoxyolean-12-ene-28-oic acid and 3β-acetoxyolean-11-oxo-12-ene-28-oic acid have been demonstrated to be active as antifeedants for the Colorado potato beetle, Leptinotarsa decemlineata.

Abundance of carabid beetles and other ground-dwelling arthropods in conventional versus low-input bean cropping systems

Abstract The abundance and seasonal dynamics of carabid beetles and other ground-dwelling arthropods in conventional and low-input dry bean ( Phaseolus vulgaris L.) cropping systems were investigated over two field seasons in Maine, USA. In 1988, carabids and staphylinids were significantly greater in number in the low-input plots. Staphylinids and arachnids were significantly more abundant in the low-input plots in 1989. Elaterid adults were abundant in 1988, and the number in the conventional plots was 23 times higher than in the low-input plots. Multivariate analysis showed that compositions of major ground-dweling arthropods differed significantly between the two cropping systems from the early to middle season of plant growth. Individual carabid species differed between the two cropping systems. Harpalus rufipes, Pterostichus melanarius, Agonum muelleri, Clivina fossor, Carabus memoralis, Carabus auratus , and Loricera pilicornis were dominant carabid species in this study. In 1988, Pterostichus melanarius, Carabus auratus , and L. pilicornis were significantly more abundant in the low-input plots, while A. muelleri and Clivina fossor were significantly more abundant in the conventional plots. In 1989, however, only A. muelleri was significantly different between cropping systems and a significantly higher number was trapped in the low-input plots.

Antifeedant activity of citrus limonoids against Colorado potato beetle: comparison of aglycones and glucosides

The importance of plant allelochemicals in plantherbivore interactions is well known. Although some of these phytochemicals act as phagostimulants for specific herbivores, the majority of allelochemicals examined appear to function primarily in plant defense, acting as insect antifeedants, growth regulators, and/or toxins (Jermy, 1966; Bernays & Chapman, 1977). As such, these chemicals have great potential for use in pest management, either directly, as natural plant protectants, or as models for the development of synthetic products. Citrus limonoids, a group of terpenoid allelochemicals found in the plant family Rutaceae have previously been shown to act as insect antifeedants (Klocke & Kubo, 1982; Alford et al., 1987; Mendel et al., 1991) as well as mammalian anticarcinogens (Lam & Hasegawa, 1989; Miller et al., 1989). They are also useful as chemotaxonomic markers (Hasegawa & Miyake, 1996). Thus, citrus limonoids are important functional chemicals in agriculture and medicine. Limonoid aglycones, which are present in young and growing citrus tissues, are converted to their respective 17β-D-glucoside derivatives during late stages of fruit growth and maturation (Hasegawa et al., 1991; Fong et al., 1992). Limonoid glucosides, such as limonin 17β-D-glucopyranoside, are accumulated in mature fruit tissues and seeds as major secondary metabolites (Fong et al., 1989; Hasegawa et al., 1991). Thirty-six limonoid aglycones and 17 limonoid glucosides have been isolated from Citrus and its hybrids, yet few have been investigated for their biological activities. None of the limonoid glucosides have previously been examined for antifeedant activity against insects. In this study we compared the antifeedant activity of limonoid aglycones and glucosides against Colorado potato beetle, Leptinotarsa decemlineata (Say), larvae.

Effects of epilimonol and starvation on feeding and oviposition by Leptinotarsa decemlineata

Epilimonol, a limonin derivative, was tested in short and long term feeding bioassays against Colorado potato beetles, Leptinotarsa decemlineata (Say), for feeding reduction and ovipositional suppression. At dosages of 10 to 30 μg/cm2, epilimonol reduced feeding by 42% to 65% in short term no‐choice assays. However, beetles did not strongly select untreated potato leaf discs over epilimonol‐treated (10 μg/cm2) ones in short term choice assays. In long term tests, epilimonol at 10 μg/cm2 remained effective against feeding, caused mortality, and suppressed oviposition. Starvation (> 16 hours/day) also caused mortality and suppressed oviposition.

Citrus limonoid effects on Colorado potato beetle larval survival and development

The effects of citrus limonoids, applied topically to potato (Solanum tuberosum L. var. ‘Katahdin’) foliage, on Colorado potato beetle (Leptinotarsa decemlineata (Say) (Chrysomelidae) larval development, growth, and survival were quantified in laboratory assays and a small‐plot field test. In laboratory assays, survival, development rate, and body weight decreased with increasing limonoid concentration, however these measures of larval response did not significantly differ among varying periods of limonoid exposure (three, six, or nine days). Significant limonoid application concentration and frequency effects on survival, development rate, and defoliation were observed in the field test. These results indicate the potential utility of lethal and non‐lethal effects of citrus limonoids for management of the Colorado potato beetle.

Bacillus thuringiensis var. israelensis δ-endotoxin: evidence of neurotoxic action

Abstract The neurotoxic, cytolytic, and lethal properties of a 25-kDa protein isolated from the δ-endotoxin of Bacillus thuringiensis subsp. israelensis (Bti) were compared with those of the alkaline-dissolved whole extract of the δ-endotoxin and the cytolytic enzyme phospholipase A 2 . In situ electrophysiological measurements of the ventral nerve cord of larval Trichoplusia ni treated at 15 and 25°C with various dosages of the three protein preparations showed that only the whole extract of the δ-endotoxin induced hyperexcitation. When the appearance of lactate dehydrogenase activity in the haemolymph of toxin-injected larvae was used to quantitate cell lysis, the cytolytic 25-kDa protein was found to be a potent cytotoxic factor like phospholipase A 2 , whereas cytotoxicity of the whole δ-endotoxin extract was relatively low. Bioassays at 28, 17, and 9°C demonstrated a positive temperature correlation with mortality for the whole toxin extract, but showed inverse correlations for the two cytolytic materials. This and previous studies indicate that insect mortality is not solely due to the cytolytic activity of the Bti δ-endotoxin upon injection into T. ni . An unidentified neurotoxic factor(s) exists within the Bti δ-endotoxin which induces hyperexcited activity in the insect nervous system. This and/or other factors impart the δ-endotoxin with biological and physiological activities different from the isolated cytolytic component.

The extraction and partial purification of a rhamnosidase from Colorado potato beetle larvae (Leptinotarsa decemlineata (Say))

An enzyme which hydrolyzed a terminal rhamnose moiety from α-chaconine was extracted and partially purified from Colorado potato beetle (CPB) (Leptinotarsa decemlineata) larvae. This ammonium sulfate precipitated enzyme fraction resulted in nearly 97% metabolism of α-chaconine after a 144 hour incubation period at 42 C as determined by high performance liquid Chromatographic (HPLC) analysis. Approximately 81% of the metabolized α-chaconine was detected asβ2-chaconine. The isolated enzyme fraction from CPB larvae exhibited no metabolism of α-solanine. Metabolism was also followed over time by thin layer chromatography (tlc).CompendioUna enzima que hidroliza la porción terminal de la rhamnosa de α-chaconina fue extraída de larvas del escarabajo de la papa de Colorado (CPB) (Leptinotarsa decemlineata) y purificada parcialmente. Esta fracción de enzima, precipitada con sulfato de amonio, dió lugar a casi 97% de metabolismo de α-chaconina después de un período de incubación de 144 horas a 42°C lo que fue determinado por cromatografía líquida de gran precisión (HPLC). Aproximadamente el 81% de la α-chaconina metabolizada fue detectada como β2-chaconina. La fracción de enzima aislada de las larvas del CPB no exhibió ningún metabolismo de α-solanina. Durante todo el tiempo se siguió también el metabolismo por medio de cromatografía de capa delgada (tlc).