Robert Delorme

Esterase metabolism and reduced penetration are causes of resistance to deltamethrin in Spodoptera exigua HUB (Noctuidea; lepidoptera)

Abstract Using deltamethrin in toxicological experiments we have shown that a guatemalian strain of Spodoptera exigua has an LC 40 at least 100 times that of a sensitive one. Delayed penetration and cleavage of deltamethrin at the ester bond are two mechanisms responsible for this resistance. Degradation of deltamethrin is 17 times higher in the resistant strain compared to the sensitive one. This degradation is inhibited by DEF and paraoxon, indicating that esterases are likely involved in the metabolism of this insecticide. In addition it has been shown that the resistant strain has an enhanced esterase activity toward chromogenic substrates, such as naphthyl acetate or methylumbelliferyl acetate, the level depending on the substrate used. It is likely that activity toward chromogenic substrates and the hydrolysis of deltamethrin are related.

Communication to the Editor Insecticide Resistance in a Strain of Aphis gossypii from Southern France

A strain (R) of Aphis gossypii from Southern France was found to be resistant to several insecticides, particularly to pirimicarb, as compared to a susceptible strain (S). Resistance levels were determined by biological tests, and the highest resistance factor (1350) was for pirimicarb. Resistance was mainly restricted to anticholinesterase inhibitors. Use of synergists, DEF and PB, suggested that resistance mechanisms based on detoxification were involved to a minor extent, since a good correlation was observed between I50 values and ki values of AChE and in-vivo bioassay data. The two strains differed in esterase activity, with a 27·7-fold increase in the R strain. Resolution of esterases by polyacrylamide gel electrophoresis showed different patterns in the S and R strains, and two isozymes were less sensitive to pirimicarb in the S strain; however, no in-vitro degradation of [14C]pirimicarb was observed. These data suggest that the main mechanism of resistance was through a decrease in the sensitivity of the target, AChE, to the insecticides.

Cyphostemmins A-B, two new antifungal oligostilbenes from Cyphostemma crotalarioides (Vitaceae)

Abstract Two new antifungal resveratrol dimers, cyphostemmins A-B (1–2), have isolated from the roots of Cyphostemma crotalarioides planch (Vitaceae) together with resveratrol 3 and previously known reseveratrol dimers (4–7). Structures of these new compounds have been established on the basis of their MS and 1H and 13C NMR spectroscopic data.

A Genetic Analysis of Mancozeb Resistance in Typhlodromus Pyri (Acari: Phytoseiidae)

A field population of Typhlodromus pyri (Acari: Phytoseiidae) tolerant to mancozeb was selected in the laboratory. After 10 mancozeb selections the LC50 value for mancozeb was 73 times higher in the selected-10 strain compared to the standard susceptible strain. A genetic analysis using reciprocal crosses and backcrosses of female F1 progeny found no maternal effect. Resistance in the selected-10 strain was codominant in expression, dominance value was about −0.1. Backcrosses between F1 females and the susceptible strain indicate that the resistance to mancozeb could be principally conferred by a predominant gene, but additional factors would also be involved.

Antifungal activity of resveratrol oligomers from Cyphostemma crotalarioides

Resveratrol and its oligomers: e-viniferine, gnetin C, Pallidol and gnetin E, as well as three new dehydrodimers, cyphostemmines A–C, have been isolated from the roots of Cyphostemma crotalarioides (Ampelidaceae). Such compounds have not been reported previously in the family Ampelidaceae. Cis e-viniferin has also been characterized as a minor component of the extract; it may have undergone partial transformation in solution into trans e-viniferin. ©1999 Society of Chemical Industry

Pyrethroids and organochlorines resistance in cotton aphid Aphis gossypii (Glov.) (Homoptera: Aphididae) in the Sudan Gezira

Abstract The resistance to insecticides of six Sudanese strains of Aphis gossypii (Glov.) collected from cotton fields in Sudan Gezira over four consecutive crop seasons (1988, 1989, 1990, 1991) and that of two French strains, was studied in the laboratory. When compared with a known English susceptible strain, Sudanese aphids were found to be resistant to the four insecticides tested (fenvalerate, deltamethrin, endosulfan and γ‐HCH) while the French strains were relatively susceptible. Evolution of insecticide resistance in Sudanese strains over the four crop seasons was observed. The high synergist ratios and the decrease in resistance factor for the resistant strain, Sudan V, in experiments with piperonyl‐butoxide (PB), an inhibitor of mixed function oxidase, and pyrethroids (deltamethrin and fenvalerate) and also PB with organochlorines (endosulfan and γ‐HCH), suggested that enhancement of the activity of this class of enzyme was a cause of resistance in the Sudanese strain of A. gossypii.

Oviposition of resistant and susceptible strains of Drosophila melanogaster in the presence of deltamethrin

Oviposition of three strains of Drosophila melanogaster in the presence of deltamethrin was observed. These strains had different levels of physiological susceptibility to deltamethrin. Two‐choice tests were conducted with couples of flies in petri‐dish arenas containing two oviposition dishes. On the first day of the experiment, females were given a choice between a treated oviposition dish and an untreated control dish. On the second day of the experiment, two control oviposition dishes were given to females. Although individual females showed a tendency to aggregate their eggs in one of the dishes, control experiments demonstrated an overall equal distribution of eggs between the dishes. When one of the two oviposition dishes in the arena was treated with deltamethrin, the percentage of females ovipositing and the mean number of eggs laid by females were reduced, compared with control arenas. Females avoided the treated oviposition dish and laid significantly more eggs on the control dish. Furthermore, when the deltamethrin concentration was increased on the first day, female flies postponed their oviposition and laid significantly more eggs on the second day. The resistant strain, SR, demonstrated the same capacity to select the untreated site for oviposition as the susceptible strain, but it showed a smaller oviposition reduction and egg retention. The relationship between physiological and behavioural susceptibility to deltamethrin is discussed.

Insecticidal activity of daphnane diterpenes from Lasiosiphon kraussianus (Meisn) (Thymelaeaceae) roots

A methanol extract of roots of Lasiosiphon kraussianus (Meisn) (Thymelaeaceae) showed potent insecticidal activity against Aphis gossypii (Glov) and Drosophila melanogaster (Meig). Bioassay-driven fractionation of this extract led to the isolation and characterisation of two known daphnane diterpenoids: Excoecaria toxin (1) and wikstrotoxin D (2). The two natural products were inferior to methomyl in activity against A gossypii and Myzus persicae (Sulz) in contact assays but were superior in ingestion assays against D melanogaster. This is the first report on insecticidal activities of compounds 1 and 2. AChE was insensitive to the two natural products.