Leaf nutrient levels and the spatio-temporal distributions of Plutella xylostella and its larval parasitoids Diadegma insulare and Microplitis plutellae in canola

Abstract

Seasonal distribution patterns of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), and its principal parasitoids Diadegma insulare (Cresson) (Hymenoptera: Ichneumonidae) and Microplitis plutellae (Muesebeck) (Hymenoptera: Braconidae) were investigated over three site-years in commercial fields of canola (Brassica napus L.) in southern Alberta, Canada. The sampling of P. xylostella, D. insulare, and M. plutellae from points arranged in grid patterns, together with the mapping and analysis of their spatial distributions over time, generated a detailed picture of the pattern of crop infestation by the herbivore and its parasitoids. Plutella xylostella exhibited significant aggregations on different scales most often when its host plants were in early flowering. Diadegma insulare adults exhibited significant aggregated distributions during early flowering and distributions subsequently became more uniform as the wasps moved into the crop later in the season. However, M. plutellae distributions were aggregated in mid flowering in only one site-year. The close spatial associations between densities of D. insulare and P. xylostella indicated that host abundance was the main determinant of parasitoid distribution patterns. Spatial distributions of nutrient contents in leaf tissue and their spatial associations with the herbivore and parasitoids were also investigated. Significant spatial associations existed between certain nutrients (e.g. nitrogen, sulfur, and potassium) and P. xylostella distributions. Sulfur exhibited a positive effect on the distributions of D. insulare but not of M. plutellae. We observed similar relationships between nutrients and the distribution of P. xylostella parasitoids as for nutrients and P. xylostella, but these relationships lacked consistency and may be the results of the spatial associations between the parasitoids and their hosts. Aggregated distributions of adults and larvae of P. xylostella hold promise for spatially targeted insecticidal applications as a means for reducing the environmental impact of insecticides on nontarget and beneficial species in canola agroecosystems.

Modeling the Integration of Parasitoid, Insecticide, and Transgenic Insecticidal Crop for the Long-Term Control of an Insect Pest

“…Sarfraz et al (2005) reviewed the biology of D. insulare. concluded that D. insulare is a good searcher for diamondback moth larvae, and Sarfraz et al (2010) found that the female parasitoids are distributed spatially according to the spatial distribution of diamondback moth density. Harcourt (1986) studied diamondback moth and D. insulare in southern Ontario using 74 generational life tables.…”

Parasitism and developmental parameters of the parasitoid Diadegma majale (Gravenhorst) in control of Plutella xylostella (L.) on selected cultivars of canola

“…This pest has developed resistance to organophosphates (Noppun et al 1986), carbamates (Sun et al 1978), synthetic pyrethroids (Liu et al 1981(Liu et al , 1982Noppun et al 1986), Bacillus thuringiensis Berliner preparations, and several other insecticides (Tabashnik et al 2003;Sarfraz et al 2006), although no study has been carried out concerning resistance of P. xylostella populations to insecticides in Iran. Failure of insecticides to successfully control P. xylostella has prompted the use of alternative approaches such as host plant resistance and biocontrol agents (Sarfraz et al , 2006(Sarfraz et al , 2010. Insect resistant plants may have direct effect on pests by reducing their initial infestations and decreasing survival, or they may have an indirect effect by increasing the exposure of the insect to its natural enemies as a result of prolonged developmental time (Sarfraz et al 2007(Sarfraz et al , 2010Ebrahimi et al 2008).…”

“…Failure of insecticides to successfully control P. xylostella has prompted the use of alternative approaches such as host plant resistance and biocontrol agents (Sarfraz et al , 2006(Sarfraz et al , 2010. Insect resistant plants may have direct effect on pests by reducing their initial infestations and decreasing survival, or they may have an indirect effect by increasing the exposure of the insect to its natural enemies as a result of prolonged developmental time (Sarfraz et al 2007(Sarfraz et al , 2010Ebrahimi et al 2008).…”

Bottom-up effects of Brassica napus nutrition on the oviposition preference and larval performance of Ceutorhynchus obstrictus (Coleoptera: Curculionidae)

“…While the relative supplies of N and S have been recognized as important for Brassica specialists in the choice of oviposition sites and larval fitness Sarfraz et al 2009Sarfraz et al , 2010, responses of these crucivores do not consistently support either the plant vigor or plant stress hypotheses. The spatial distributions of C. obstrictus adults and larvae in commercial fields have been associated with areas of high S and low N contents in plant tissue .…”