Abundance, growth rate and parasitism of Brevicoryne brassicae and Myzus persicae (Homoptera: Aphididae) on broccoli grown in living mulches

Abstract

In 1990 and 1991, populations of the cabbage aphid, Brevicoryne brassicae, and the green peach aphid, Myzus persicae, were monitored on broccoli interplanted with three leguminous cover crops (the living mulches) and compared with broccoli without cover crop (clean cultivation). The cover crops used were white clover ( Trifolium repens L.), strawberry clover (Trifolium fragiferum L.) and a mixture of birdsfoot trefoil (Lotus corniculatus L. ) and red clover (Trifolium praetense L.). Fertilizer was applied as compost or synthetic fertilizer crossed with cropping system regime. Brevicoryne brassicae can reach pest status in Brassica cropping systems, whereas M. persicae is generally innocuous. Both aphids are attacked by the parasitoid Diaeretiella rapae. Seasonal aphid abundance, parasitism and population growth rates were analyzed.No significant effect of fertilizer was found for any of the parameters analyzed. The living mulches had lower aphid populations overall, although differences with clean cultivation were greatest early in the season for M. persicae and diminished over time. No effect of cropping system on population growth rate was seen for Brevico ryne brassicae, but for M. persicae growth rates were higher in living mulches compared with clean cultivation. Parasitism was highest on clean cultivated broccoli for both aphid species in 1990 and for M. persicae in 1991, but no differences were found for Brevicoryne brassicae in 1991. This suggests that differential population growth rates and parasitism seen for M. persicae are a result of inhibition of D. rapae in the living mulches. Possible reasons for differences in parasitism between the two aphid species in living mulches and clean cultivation are discussed.

Traditional fertilization and its effect on corn insect populations in the Guatemalan highlands

“…Efforts by entomologists to evaluate the effects of fertilization on insect pest populations have not been conclusive. Some evidence supports the observation that organic fertilizers diminish herbivorous insect populations (Culliney and Pimentel, 1986;Eigenbrode and Pimentel, 1988;Listinger, 1993;Phelan et al, 1995), whereas other reports suggest that organic fertilizers do not always diminish pest populations but even increase them (Costello, 1994;Costello and Altieri, 1995;Letourneau et al, 1996). There clearly is a lack of understanding of the relationship between organic fertilization and insect pests.…”

Varying responses of insect herbivores to altered plant chemistry under organic and conventional treatments

“…A meta-analysis found no significant effect of crop production system on herbivore species abundance, though the trend was towards higher populations under conventional production (Bengtsson et al 2005). Apart from Costello & Altieri (1995), the studies above assessed the abundance, preference or performance of just one herbivore species or presented data from a single year of a field trial, so the hypothesis of lower herbivore abundance under organic fertilizers had not been rigorously tested.…”

Plant nutrient supply determines competition between phytophagous insects

“…Brevicoryne brassicae feeds predominantly on the plant apex and young foliage [20], whereas P. xylostella larvae feed mainly on older leaves (V. Chadfield & J. T. Staley 2009, unpublished data). The two species co-occur on crucifers during the spring and early summer in the UK [21], but are unlikely to compete through interference owing to their different feeding modes and sites.…”