Bottom-up effects of host plant nutritional quality on Plutella xylostella (Lepidoptera: Plutellidae) and top-down effects of herbivore attack on plant compensatory ability

Abstract

Abstract. The plant stress and plant vigour hypotheses are competing paradigms pertaining to the preference and performance of herbivorous insects on their host plants. Tests of these hypotheses ideally require detailed information on aspects of soil nutrition, foliar nutrient levels and parameters of herbivore fitness, but such studies are uncommon. These hypotheses were tested using the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), reared on its host plant, Brassica napus (L.), grown in an experimental system of five nutrient regimes. Different levels of fertilizer treatments significantly affected the nutrient content of B. napus foliage and this in turn affected the preference and performance of P. xylostella. Ovipositing females discriminated among host plants grown in soils subjected to different fertilizer treatments and selected plants on which pre-imaginal survival was highest, development fastest and longevity of the next generation of adults the longest, even when food was scarce. Plants subjected to herbivory by P. xylostella responded by producing elevated levels of some nutrients (e.g., sulphur), but other nutrient levels declined in infested leaves (e.g., nitrogen). Regardless of the rate of fertilizer application, plants compensated for herbivory by increasing root mass compared to un-infested control plants; plants grown in soils receiving the optimum quantity of fertilizer developed the most robust root systems when infested. The plant stress and the plant vigour hypotheses are likely to be at the opposite ends of a continuum of responses between insects and their host plants. Our investigations indicate a complex set of interactions involving both bottom-up and top-down effects, which interact to affect host plant quality, oviposition site selection by female herbivores and the fitness of their offspring.

Preference and performance of Plutella xylostella (L.) (Lepidoptera: Plutellidae) on canola cultivars

“…Earlier reports suggest that differences in resistance can vary among cultivars within the same species (Hamilton et al 2005;Sarfraz et al 2007). P. xylostella respond differently to physical and chemical properties of host plants (Sarfraz et al 2006(Sarfraz et al , 2009 and ovipositional differences in this study could be attributed to physical structures and/or chemical profiles of the cultivars tested. Difference in leaf trichome density that could be related to the resistance was not discernible among Opera and Zarfam cultivars.…”

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

“…2). These results are somewhat surprising because in ovipositional preference experiments conducted in the laboratory under controlled conditions, Sarfraz et al (2009a) found that females of P. xylostella selected B. napus plants fertilized at intermediate levels of fertility relative to plants fertilized at low or high levels. Moreover, larval survival and development rates were also greatest on canola grown at intermediate fertility levels.…”

Does vegetation complexity affect host plant chemistry, and thus multitrophic interactions, in a human-altered landscape?

“…High N availability may lead to unbalanced leaf amino acid profiles or to higher organic acid concentrations in plants that could stress herbivores or may be even toxic for them (Brodbeck et al 1990;Sarfraz et al 2009b). Furthermore, fertilisation can lead to an imbalance in the protein/carbohydrate ratio because of an enhanced protein content (Cease et al 2012).…”