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. (Résumé d'auteur

Spatiotemporal distribution and impact of diamondback moth parasitoids in the Dakar Niayes in Senegal

“…However, in our study C. vestalis and Brachymeria sp had the lowest parasitism rate among the four parasitoids species and their presence in the Niayes area is uncertain (Sow et al, 2013a). However, a new DBM larval parasitoid species was reported for the first time in Senegal in 2014: Diadegma insulare (Cresson) Hymenoptera; Ichneumonidae.…”

“…Larger areas grown with cabbage during the cold dry seasons may explain this result (Altieri and Nicholls, 2004;Rusch et al, 2012). On the other hand, temperatures of the hot dry season are also very similar to the optimum temperature for DBM (Marchioro and Foerster, 2011;Sow et al, 2013a).…”

“…Parasitoid populations are usually larger when the host populations are bigger and when cabbages are more infested, because they attract more auxiliaries (Sow et al, 2013a). Additionally, cabbage damages caused by DBM larvae populations appear to have an attractive effect on specific parasitoids.…”

“…During this same season, A. litae showed a parasitism rate of 75% in the three areas (south, center and north), which was higher than the one, observed for the other three parasitoids. During this period, climate was favorable for this species whose optimum development occurs at 25 °C and low humidity (Sow et al, 2013a). Brachymeria sp the DBM pupal parasitoid identified in this study, is a facultative generalist hyperparasitoid attacking hymenopteran (Liu et al, 2000).…”

Pesticide resistance in Plutella xylostella (Lepidoptera: Plutellidae) populations from Togo and Benin

“…Our observations call for a three-way IPM approach based on (i) avoiding the use of pyrethroids and organophosphates, which would otherwise interfere with the activity of C. vestalis (Nyambo et al 2011;Sow et al, 2013a); (ii) using insect net covers, a promising technology to reduce pest damage as demonstrated in Benin (Martin et al, 2006;Martin et al, 2015); and (iii) using biopesticides such as neem extracts and the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin (Sarfraz et al, 2005;Agboyi et al, 2013;Sow et al, 2013b).…”