Egg Laying of Cabbage White Butterfly (Pieris brassicae) on Arabidopsis thaliana Affects Subsequent Performance of the Larvae

Abstract

Plant resistance to the feeding by herbivorous insects has recently been found to be positively or negatively influenced by prior egg deposition. Here we show how crucial it is to conduct experiments on plant responses to herbivory under conditions that simulate natural insect behaviour. We used a well-studied plant – herbivore system, Arabidopsis thaliana and the cabbage white butterfly Pieris brassicae, testing the effects of naturally laid eggs (rather than egg extracts) and allowing larvae to feed gregariously as they do naturally (rather than placing single larvae on plants). Under natural conditions, newly hatched larvae start feeding on their egg shells before they consume leaf tissue, but access to egg shells had no effect on subsequent larval performance in our experiments. However, young larvae feeding gregariously on leaves previously laden with eggs caused less feeding damage, gained less weight during the first 2 days, and suffered twice as high a mortality until pupation compared to larvae feeding on plants that had never had eggs. The concentration of the major anti-herbivore defences of A. thaliana, the glucosinolates, was not significantly increased by oviposition, but the amount of the most abundant member of this class, 4-methylsulfinylbutyl glucosinolate was 1.8-fold lower in larval-damaged leaves with prior egg deposition compared to damaged leaves that had never had eggs. There were also few significant changes in the transcript levels of glucosinolate metabolic genes, except that egg deposition suppressed the feeding-induced up-regulation of FMOGS-OX2, a gene encoding a flavin monooxygenase involved in the last step of 4-methylsulfinylbutyl glucosinolate biosynthesis. Hence, our study demonstrates that oviposition does increase A. thaliana resistance to feeding by subsequently hatching larvae, but this cannot be attributed simply to changes in glucosinolate content.

Perception, signaling and molecular basis of oviposition-mediated plant responses

“…Molecular or chemical changes that could explain the enhanced resistance of naturally oviposited Arabidopsis plants to P.   brassicae larvae were however not identified and further studies should explore this question. On the contrary, levels of a major anti-insect defense metabolite, the 4-methylsulfinylbutyl glucosinolate, and the expression of some glucosinolate biosynthesis genes were significantly reduced in damaged leaves with prior oviposition (Geiselhardt et al 2013), in line with the suppression of herbivore-induced genes found by Bruessow et al (2010). It would be interesting to test if natural oviposition by generalist herbivores that lay eggs on Arabidopsis triggers a similar response and whether a reduced glucosinolate content enhances larval performance, as would be expected from the known role of these metabolites.…”

“…A recent study found that P. brassicae larvae that fed on previously oviposited Arabidopsis plants consumed less leaf material, gained less weight after 2 days and suffered higher mortality than larvae feeding on plants that did not receive eggs (Geiselhardt et al 2013). Surprisingly, these results were different from the study published by Bruessow et al (2010), where P. brassicae egg extract pretreatment did not affect the performance of P. brassicae larvae after 8 days of feeding.…”

Pre-exposure of Arabidopsis to the abiotic or biotic environmental stimuli “chilling” or “insect eggs” exhibits different transcriptomic responses to herbivory

“…The egg-induced transcriptional changes of A. thaliana may also provide an ‘alert’ state which prepares the plant for improved anti-herbivore defence if eggs are not removed prior to herbivory. A study by Geiselhardt et al 32,. who did not remove P. brassicae eggs from A. thaliana leaves prior to larval feeding, indicates that eggs are taken as ‘warning’ of impending herbivory; the P. brassicae larvae performed worse on previously egg-deposited than on egg-free leaves.…”

Pseudomonas syringae enhances herbivory by suppressing the reactive oxygen burst in Arabidopsis

“…Eggs from Lepidoptera and Diptera (including Drosophila melanogaster ) can activate PTI and induce ROS accumulation and callose deposition at the site of oviposition (Bruessow et al, 2010; Gouhier-Darimont et al, 2013; Little et al, 2007), leading to reduced larval performance (Geiselhardt et al, 2013). We have here and previously observed the accumulation of ROS at the sites of feeding and oviposition by adult female S. flava , and found that egg deposition activated expression of the PTI marker gene CYP81F2 (Whiteman et al, 2011), which is typically associated with ROS accumulation (Daudi et al, 2012).…”