Laurence Arvanitakis

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.

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.

Life History Traits of Oomyzus sokolowskii Kurdjumov (Hymenoptera: Eulophidae), a Parasitoid of the Diamondback Moth

In this study the life-history of Oomyzus sokolowskii (Kurdjimov), a parasitoid of the diamondback moth (DBM) Plutella xylostella (L.) as characterized. The life cycle, adult size, fecundity, ovigeny, parthenogenesis, host age preference and host-searching behaviour by parasitoid females were studied under laboratory conditions. Oomyzus sokolowskiiapos;s life cycle lasted 15. 6 days. Sexual dimorphism was recorded, with females being bigger than males. The species is synovigenic. The parasitism rate was significantly different between mated and unmated females, which implied that mating stimulated the behaviour of parasitism. Thelythokous parthenogenesis was not recorded. Females could parasitize all larval stages and pre-pupae, but the parasitism rate was higher in the fourth larval stages of DBM. The host-seeking behaviour was influenced by host spatial patchiness; O. sokolowskii females performed better when they were placed in a 7 cm3 oviposition box. This study gives a better understanding of the life history traits of O. sokolowskii, which has been neglected in the biological control of DBM in tropical regions. The study suggests the use of O. sokolowski as a promising candidate for the management of DBM in cabbage in combination with other IPM strategies.

Performance of the parasitoid Oomyzus sokolowskii (Hymenoptera: Eulophidae) on its host Plutella xylostella (Lepidoptera: Plutellidae) under laboratory conditions

Oomyzus sokolowskii (Kurdjumov) is a gregarious larval-pupal parasitoid of the diamondback moth Plutella xylostella (L.). The objective of this study was to investigate the interactions between host and parasitoid by examining the effects of biotic factors such as gregariousness, host origin and stages, and female parasitoid age on the parasitism rate, developmental time, the number of offspring and the offspring sex ratio of O. sokolowskii under laboratory conditions. The percentage of parasitism and the number of parasitoids increased with the number of O. sokolowskii females. Oomyzus sokolowskii preferred fourth larval instars over other larval stages. The parasitism rate and the progeny production of O. sokolowskii decreased with parasitoid age; however, the developmental time and the sex ratio of the offspring were not significantly different. Our results confirm previous findings on larval preferences of O. sokolowskii. The study also confirmed the importance of geographical origin of the host on the performance of O. sokolowskii.

The relationship between the diamondback moth, climatic factors, cabbage crops and natural enemies in a tropical area

ABSTRACT The impact of abiotic and biotic factors (rainfall, temperature, host plant and natural enemies) on population dynamics of the Plutella xylostella L. diamondback moth was investigated. The experiments were conducted during the rainy and dry seasons for two years (June 2009-April 2011) on unsprayed cabbage plots in Malika (Senegal). Every 10 days, 10 cabbages were randomly selected. Plutella xylostella larvae, pupae and parasitoid cocoons were recorded on each plant. Before each sampling, the diameters and ages of plants were recorded. Temperature and rainfall were also recorded during this study. Larvae and pupae of P. xylstella were higher for the dry season than the rainy season. There was a negative correlation between temperature and P. xylostella populations, and a strong relationship between P. xylostella populations and the age of cabbages. Females oviposited on young cabbages where the presence of young larvae was important, whereas older immature stages were mainly found in older cabbage plants. Parasitoid populations were higher for the dry season than the rainy season. High temperatures did not increase the pest populations and parasitism rate. There was no effect found on pest, plants and natural enemies due to rainfall. There was a positive correlation between pest populations and parasitism. Four Hymenoptera species were found: Oomyzus sokolowskii, Apanteles litae, Cotesia plutellae and Brachymeria citrae, but they were not efficient to control the P. xylostella populations. These results are important for understanding the factors that promote or inhibit pest populations and their natural enemies, and therefore essential for effective crop protection.