The dual function of elicitors and effectors from insects: reviewing the ‘arms race’ against plant defenses

Salivary surprise: Symmerista caterpillars anoint petioles with red saliva after clipping leaves

“…Cuts in aspen leaves Populus tremula , for example, caused a burst in emission of volatiles that was six times higher when the midrib was cut than when only the lamina was severed [ 63 ]. Plant defensive responses are triggered in part by compounds regurgitated from the caterpillar gut during feeding [ 69 ] or secreted in the saliva [ 70 ]. Chewing on petioles would appear to be a particularly effective way to transmit these elicitors throughout the plant.…”

“…Caterpillars that clipped leaves or cut furrows and girdles invariably applied saliva to the wounds. In some caterpillar species, salivary constituents are known to suppress defensive pathways, thereby allowing the caterpillars to feed stealthily [ 69 , 71 ]. Almost all research on the impacts of these salivary effectors has been done on herbaceous plants such as tobacco, tomato, maize, and Arabidopsis [ 69 , 71 ], but two recent studies indicate that the saliva of tree-feeding caterpillars has similar constituents and similar effects on plant defenses.…”

“…In some caterpillar species, salivary constituents are known to suppress defensive pathways, thereby allowing the caterpillars to feed stealthily [ 69 , 71 ]. Almost all research on the impacts of these salivary effectors has been done on herbaceous plants such as tobacco, tomato, maize, and Arabidopsis [ 69 , 71 ], but two recent studies indicate that the saliva of tree-feeding caterpillars has similar constituents and similar effects on plant defenses. The first study documented that silkworms ( Bombyx mori , Bombycidae) apply droplets of saliva to leaf edges during feeding on mulberry ( Morus alba , Moraceae); the droplets form threads of silk visible in the SEM [ 27 ].…”

Molecular biology of chemical defenses

“…To be successful, those signal transduction pathways need to constantly adapt to changing environmental challenges. A review by Jones et al (2021) reflects on how chemical elicitors/effectors from insects and matching responses from plants have characterized the evolution of the two enormously diverse and prolific species. Several examples are given that warn against a simplified view of insectderived chemicals as mere elicitors/effectors of plant defense responses, but rather as also influencing insect species at the same time.…”

Proteinaceous elicitor from a secretion of egg‐laying insect herbivore induces plant emission that attracts egg parasitoids

“…The coevolution and arm's race between plants and their herbivores have been a driving force for plant chemical ecology research (Agrawal & Zhang, 2021 ; Jones et al, 2021 ). Chemical defence compounds produced by plants may directly affect the feeding or egg‐laying of insects by disturbing their behaviour and food digestion or indirectly by attracting the natural enemies of the herbivorous insect (Johnson, 2011 ).…”