Combining ecological methods and molecular gut‐content analysis to investigate predation of a lepidopteran pest complex of Brassica crops

Abstract

In South East Queensland, Australia, Brassica crops are typically attacked by Crocidolomia pavonana Fabricius (Lepidoptera: Crambidae) in late summer and autumn (February to May) and by Plutella xylostella L. (Lepidoptera: Plutellidae) and Pieris rapae L. (Lepidoptera: Pieridae) from late autumn to the end of spring (May to November). Physical exclusion studies were used to assess the impact of predators on pest populations in two cabbage [Brassica oleracea L. var. capitata cv. Warrior (Brassicaceae)] crops grown sequentially between April and September 2006. The studies were complemented by molecular gut-content analysis of predators simultaneously hand-collected from the study crops by destructive sampling of cabbage plants. In May 2006, exclusion studies showed that 57% (95% CI = 40-74%) of the C. pavonana study cohort was lost to predation. Spiders represented 81% of all predators collected and Lycosidae collected from the soil surface beneath sampled plants dominated (61% of predators); 23% of Lycosidae contained C. pavonana DNA, whereas 5% contained P. xylostella DNA. In August 2006, exclusion studies showed that 88% (95% CI = 83-93%) of the P. xylostella cohort was lost to predation. Spiders represented 99% of all predators collected; soil surface dwelling Lycosidae (51% of predators) dominated, followed by Linyphiidae (20%) and foliar-dwelling spiders (16%; Theridiidae, Salticidae, Clubionidae/Miturgidae, and Oxyopidae combined); 12% of Lycosidae and 38% of foliar-dwelling spiders contained P. xylostella DNA. Life tables for P. xylostella that were constructed for cohorts exposed to predators and cohorts from which predators had been physically excluded showed that eggs and neonates suffered the highest rates of predation. In a concurrent study, P. xylostella that were naturally recruited to the field population suffered similar high levels of early-stage mortality.

Knowing your enemies: Integrating molecular and ecological methods to assess the impact of arthropod predators on crop pests

“…The challenge now is to exploit the wealth of diagnostic techniques available and effectively unite them with this type of quantitative approach to identify predators with the capacity to suppress pest populations. This has recently been done to quantify the impact of different natural enemies on lepidopteran pests of Brassica crops (Furlong et al ., ) and the approach provides a suitable framework for similar assessments of the impacts of natural enemies of pests in other agroecosystems. Such studies are essential if the endemic predatory fauna in any agroecosystem is to be exploited within IPM as, in order to utilize this natural resource effectively, the identity of key predator groups needs to be known so that specific conservation practices can be designed and their populations manipulated for improved and sustainable pest management.…”

Landscape ecology and expanding range of biocontrol agent taxa enhance prospects for diamondback moth management. A review

“…Predators can play an important role in controlling diamondback moth as shown in work in various countries including the USA (Muckenfuss et al 1992), Australia (Furlong et al 2004a), China (Liu et al 2005), and North Korea (Furlong et al 2008a), though their impact is contingent on avoiding pesticide-induced mortality of the agents. Recent work shows that diamondback moth predators, which principally attack early instars, and parasitoids which typically attack second instar and older larvae, can complement each other and that resource partitioning among these taxa can minimize intraguild predation (Furlong et al 2014).…”

Identifying critical research gaps that limit control options for invertebrate pests in Australian grain production systems

“…McDonald et al 2014). Natural enemies can be effective at reducing P. xylostella populations (Liu et al 2004;Furlong et al 2004a;Furlong & Zalucki, 2007;Furlong et al 2014), but widespread insecticide use can make them less effective. 1).…”

“…However, economic impact thresholds in canola, sequential sampling plans (Hamilton et al 2004) and a resistance management strategy (Roush et al 1998) have been developed for this species. Natural enemies can be effective at reducing P. xylostella populations (Liu et al 2004;Furlong et al 2004a;Furlong & Zalucki, 2007;Furlong et al 2014), but widespread insecticide use can make them less effective. There is little understanding about the dynamics of predators of P. xylostella, but some studies on parasitoids in brassica crops have produced useful information for growers (Furlong et al 2004a).…”