Chemical compositions of leaf extracts from Conocarpus erectus L. (Combretaceae) and their bioactivities against Tribolium castaneum Herbst (Coleoptera: Tenebrionidae)

Botanical insecticides have long been considered as alternatives to synthetic chemical insecticides in IPM programs. Effects of aqueous and ethanolic extracts obtained from buttonwood, Conocarpus erectus L. (Combretaceae), leaves on a major kind of stored product pests, Tribolium castaneum Herbst (Coleoptera: Tenebrionidae), were evaluated under laboratory conditions. For this purpose, LC₅₀, repellency, antifeedant properties, and some biological effects (including body weight, immature developmental time and survival) of the insect were determined. The aqueous and ethanolic extracts were highly toxic to the larvae and adults. Calculated LC₅₀ values ranged between 2.6 and 193.4 (g/kg). Both extracts had repellent and antifeedant properties against the adults. The extracts adversely affected the larval and pupal weights, developmental time, and survival. Aqueous extracts were more effective only for the LC₅₀ values and only in females. All other measured parameters do not differ between the two extracts. The bioactive properties might be related to high amounts of alkaloid, phenol and tannin. Aqueous extract of the plant leaves may be a useful alternative for chemical insecticides.     

Recognition and avoidance of insecticide-treated Scots Pine (Pinus sylvestris) by Hylobius abietis (Coleoptera: Curculionidae): implications for pest management strategies

Abstract 1 The feeding preferences of Hylobius abietis (L.) were studied in a series of choice and no‐choice trials for insecticide‐treated food, time‐to‐death studies and arena trials. 2 Treatment of Scots Pine twigs with a pyrethroid insecticide, lambda‐cyhalothrin, was compared with twigs treated with imidacloprid, a neonicotinoid. 3 Clear avoidance of insecticide‐treated food sources, with strong evidence of selection for untreated food sources, was shown. 4 In addition, it took up to 3 weeks for H. abietis to die from insecticide poisoning when fed on treated food and, during this time, it was potentially capable of finding new untreated food sources.     

Ecdysteroid resistant subclones of the epithelial cell line from Chironomus Tentans (insecta, diptera). I. Selection and characterization of resistant clones

Summary Chironomus tentans cells were cultured in the presence of gradually increasing concentrations of 20-OH-ecdysone or a nonsteroidal molting hormone agonist, the benzoylhydrazine RH 5992, for a period of about 2 yr. From these cultures, subclones were selected, which are resistant to up to 25 μM 20-OH-ecdysone according to morphological (changes in cell shape and cell arrangement) and physiological criteria (acetylcholinesterase induction, secretion of chitinolytic enzymes, thymidine incorporation). Some subclones, selected in the presence of 20-OH-ecdysone, are resistant only to molting hormone, but still respond to RH 5992 morphologically and biochemically, whereas subclones selected in the presence of the benzoylhydrazine showed no reaction neither to 20-OH-ecdysone nor to the hormone agonist. Hormone resistance is stable; 3 mo. after hormone withdrawal, resistant clones still do not respond to renewed exposure to 20-OH-ecdysone or RH 5992, respectively. Because in all resistant subclones tested so far all hormonally regulated responses known from sensitive cells were no longer detectable, it is assumed that the hormone signaling pathway itself is interrupted. Possible mechanisms of hormone resistance were discussed.     

Lethal and sub‐lethal effects of faecal deltamethrin residues on dung‐feeding insects

Endectocides administered to livestock to facilitate pest and parasite control may be excreted in the faeces at concentrations that are toxic to coprophagous insects, including species of ecological importance. Although much research has focused on the effects of macrocyclic lactones, relatively less attention has been given to any similar impacts of the widely used pyrethroid insecticides. Here, the effects of faecal residues of the pyrethroid deltamethrin after application to Holstein–Friesian cattle in a proprietary pour‐on formulation are examined. Freshly dropped dung was collected 1, 3, 5 and 7 days after treatment and from an untreated control group. In laboratory bioasssays, female Lucilia sericata (Diptera: Calliphoridae) blow flies matured significantly smaller egg batches and had a lower percentage of eggs hatch after feeding on dung collected for up to 5 days after treatment, compared with flies feeding on dung from untreated cattle. In the field, artificial dung pats were constructed from the collected dung and left on pastureland for 7 days before being retrieved and searched for insects. Significantly more adult Diptera emerged from the faeces of untreated cattle than from the dung of treated cattle collected on days 1 and 3 after treatment. Adult Coleoptera were found in lower numbers in the dung of treated animals compared with control dung, suggesting a repellent effect. The results indicate that deltamethrin residues in cattle faeces have a range of lethal and sub‐lethal effects on dung‐feeding insects for up to a week after treatment, but that the precise duration and nature of toxicity varies depending on the sensitivity of the insect in question.     

Genetic analysis of resistance to azinphosmethyl in the pear psylla Cacopsylla pyri

Laboratory selection with azinphosmethyl had little effect on the chemical resistance in Cacopsylla pyri strains, in comparison to the original wild populations. The resistance ratio relative to a susceptible strain varied from 10- to 40-fold depending on the generation studied. Crosses between two resistant strains and the susceptible strain show resistance to be autosomally inherited and semi-dominant in expression. Backcrosses between F1 and the susceptible strain were unable to distinguish unabigously between monogenic and polygenic inheritance. In the majority of experiments, however, the overall dose-response relationship for backcross progeny was consistent with a single gene hypothesis. Additional bioassays showed azinphosmethyl-resistant strain to cross-resistant monocrotophos and phosmet, but not carbamates, pyrethroids, amitraz or the organophosphates chlorpyrifos and mevinphos.     

Testing Anopheles albimanus for genetic linkage of insecticide resistance genes by combining insecticide bioassay and biochemical methods

A microtitre-plate assay which distinguishes propoxur-resistant from susceptibles Anopheles albimanus Weidemann was used to test for linkage between the genes for propoxur- and dieldrin-resistance. The adult progeny of a backcross between a doubly-resistant colony and a fully susceptible colony were exposed in conventional test kits to the standard discriminating dose of dieldrin, and kept in the insectary overnight. Both live and dead insects were then assayed individually for propoxur-resistance. The results showed that heterozygotes for propoxur-resistance could be reliably distinguished from susceptibles whether or not they had been killed up to 24 h previously by dieldrin treatment. In this way all the backcross progeny could be scored at both resistance loci, and all four genotypic classes identified. Resistant and susceptible alleles at the two loci were inherited independently, demonstrating the absence of linkage. The usual method of testing for linkage between resistance genes is inefficient and open to bias, because insects have to be exposed to each insecticide in turn, and only half of them can be scored at both loci. The method shown here avoids these drawbacks.