Dominique Bordat

Population dynamics of Plutella xylostella (Lep., Yponomeutidae) and its parasitoids in the region of Brasilia

Abstract: The diamond back moth Plutella xylostella (L.) is the most serious pest of Brassicaceae in the world. It is resistant to many insecticides which has led to a search for alternative techniques of control, principally biocontrol‐based pest management. The impact of P. xylostella and its parasitoids was analysed in a 6‐month study of cabbage crops in the Brasilia region of Brazil, from June to November 1998. The population of the pest and its guild of parasitoids were quantified on two experimental plots at the Embrapa‐Hortaliças research station by weekly samplings. In the first cropping (June to early September), populations of P. xylostella followed a logistic growth curve leading to the destruction of the crops. In the second cropping, rains prevented the development of P. xylostella. Seven species of parasitoids were observed, Diadegma leontiniae (Brethes) and Apanteles piceotrichosus (Blanchard) being dominant. Cotesia plutellae (Kurdjumov) and Actia sp., previously more abundant, became very minor parasitoids. Significant differences were observed in specific parasitism rates between the plots. The combined parasitism rates were identical on both plots (around 23%) and were insufficient to regulate the populations of P. xylostella. Six species of hyperparasites were reared from Diadegma leontiniae and Apanteles piceotrichosus, showing a high diversity of natural enemies in this region of recent colonization by P. xylostella.

Comparative Effects Of Deltamethrin And Neem Kernel Solution Treatments On Diamondback Moth And Cotesia Plutellae (Hym., Braconidae) Parasitoid Populations In The Cotonou Peri-Urban Area In Benin

A comparison between deltamethrin and Neem kernel solution treatments on Plutella xylostella (L.) populations was made in the Cotonou peri‐urban area. Diamondback moth populations were 10 times larger in deltamethrin plots, than in Neem plots after treatment. The number of marketable cabbages from Neem‐treated plots was 1.5 times greater than the number from deltamethrin‐treated plots. There was no apparent effect of either treatments on Cotesia plutellae (Kurdjumov) populations, the only parasitoid of the pest that was present in the area.

Genetic differentiation among various populations of the diamondback moth, Plutella xylostella (Lepidoptera: Yponomeutidae)

Genetic variation among 14 populations of Plutella xylostella (Linnaeus) from USA (Geneva, New York), Brazil (Brasilia), Japan (Okayama), The Philippines (Caragan de Oyo), Uzbekistan (Tashkent), France (Montpellier), Benin (Cotonou), South Africa (Johannesburg), Réunion Island (Montvert), and five localities in Australia (Adelaide, Brisbane, Mareeba, Melbourne, Sydney) were assessed by analysis of allozyme frequencies at seven polymorphic loci. Most of the populations were not in Hardy-Weinberg equilibrium and had a deficit in heterozygotes. The global differentiation among populations was estimated by the fixation index (Fst) at 0.103 for the 14 populations and at 0.047 when populations from Australia and Japan, which differed most and had a strong genetic structure, were excluded from the analysis. By contrast, the populations from Benin (West Africa) and Brazil (South America) were very similar to each other. Genetic differentiation among the populations was not correlated with geographical distance.

Biology of Diadegma sp. (Hymenoptera: Ichneumonidae), a parasitoid of Plutella xylostella (L.) (Lepidoptera: Yponomeutidae), from Reunion Island

The genus Diadegma have some species able to parasite Plutella xylostella (L.) (DBM). Laboratory studies were carried out on a Diadegma sp. from Reunion Island to elucidate its ability to parasite DBM larvae, and to determine the influence of the temperature on its fecundity, longevity, oviposition and the consumption of cabbage leaves by parasitized DBM larvae. Parasitism rates were close to 70% for the L2 and L3 instar, and 53% for the L4. At 15°C, there were no progeny. At 20°C and 25°C, the percentage of parasitism was near 70%. At 29°C, the percentage parasitism was similar but the number of males produced was higher. Parasitized DBM larvae consumed 35% less leaf surface than non parasitized larvae. This Diadegma sp. is a possible candidate for introduction into tropical areas, where no tropically adapted Diadegma species are known and could complement Bacillus thuringiensis treated systems.

Chemical characterization of contact semiochemicals for host-recognition and host-acceptance by the specialist parasitoid Cotesia plutellae (Kurdjumov)

Summary.Cotesia plutellae is a specialist parasitoid of Plutella xylostella. This specificity is potentially under the control of several factors before and after oviposition. Thereby, the stimuli that lead female parasitoids to host locations and to oviposition, might be at the basis of the specificity. We explore here the response of C. plutellae females exposed to host cuticular lipids. A total cuticular lipid extract of host caterpillars was fractionated into a hydrocarbon fraction and a non-hydrocarbon fraction. Neither fraction alone had any effect on oviposition behaviour in C. plutellae but the hydrocarbon fraction alone did seem to have a positive effect on the rate of antennal contact by the females. To induce oviposition behaviour, both fractions were necessary and reflect cooperation between at least one compound in each fraction. Identification of cuticular lipids shows that hydrocarbons were dominant (77%). Non-hydrocarbon compounds were mainly represented by 15-nonacosanone (18% of the total lipid extract). This ketone is rare in insect cuticle lipids and is thought to originate from the cabbage epicuticle where it is dominant with n-C29 and 14- and 15-nonacosanol also found among the cuticular lipids of the host caterpillar.

Efeito de Bacillus thuringiensis Berliner e inseticidas químicos sobre a traça-das-crucíferas, Plutella xylostella (L.) (Lepidoptera: Yponomeutidae) e seus parasitóides

Three biopesticides based on Bacillus thuringiensis (Dipel, Florbac and Biobit), and two chemical insecticides (deltamethrin and abamectin) were evaluated in field trials against Plutella xylostella (L.) and its parasitoids in Brazil. Plots treated with Florbac, Biobit and abamectin produced 100% marketable cabbages. Dipel and deltamethrin also resulted in acceptable control (85% yield). In the control plot, 97.2% of the yield was lost. The rate of parasitism on the plots treated with biopesticides was between 35.7 and 60.5%, in the control was 42.9% and in those treated with chemical insecticides was 9.0 and 25.8 %. These results indicate that the biopesticides had no adverse effect on the parasitoids, in contrast to the classic chemical products.

Variabilidade genética de Diadegma sp., parasitóide da traça-das-crucíferas, através de RAPD-PCR

The genus Diadegma has species that are parasitoids of larvae of diamondback moth, Plutella xylostella, one of the most important pests of Brassicacea. This genus has a worldwide distribution. Representative samples of three Diadegma populations from Brazil, Reunion Island and Malaysia were characterized by RAPD-PCR. No intra-population variability was found. However, the high coefficient of genetic similarity between the populations suggests that they could belong to different species.