coevolved systems. An epic allusion can be found in Charles Darwin’s book “On the
Origin of species.” He states that these plant-insect interactions could date back to
the Devonian period (420 million years ago [Mya]), as plants established themselves
on land. Plant-insect interactions became prominent in the Carboniferous period
(250–320 Mya) which is characterized by the appearance of insect pollination and
continue to dominate even today [1]. These interactions have resulted in a vast
diversification of plant and insect species [2].
The first evidence of plant-insect interaction is that of pollinivory and goes as far
back to the early Permian era (298 Mya) [3]. Furthermore, the emergence of
angiosperms is followed by an immediate shortfall of insect diversity. This can be
attributed to the time taken by insects to adapt and start feeding on seeds and fruits.
The advent of terrestrial plants caused insects to develop mouthparts that assisted
them to feed on seeds and other plant parts. Nectar-consuming insects (Hymenoptera
and Lepidoptera) came into existence in the late Cretaceous period after the appearance of pollen and nectar-producing plants (early Cretaceous period) [2]. Thus,
plants and their composition have a great influence on insect evolution.
The key feature in the success of these interactions is the adaptability of plants
and insects to generate diverse chemical compounds and utilize them for their
survival. The various chemicals synthesized by plants attract insects for pollination
or parasites for pest infestation. In addition, the arena of plant chemicals also acted as
defense compounds against herbivorous insects [4]. Depending on the level and type
of insect attack, plants modulated the production and distribution of these defense
metabolites. In response to this, insects developed functional survival tactics like
sequestration, detoxification, and repellence to combat negative or toxic effects of
defensive secondary metabolites [5]. The stress of toxic metabolites on insects
induced selection pressure that led to the emergence of resistance to phytochemicals.
Thus, mutualistic coevolution turned into a molecular warfare that resulted in the
generation of vast diversity in plant secondary metabolites [6] (Fig. 1).
Here, we are discussing various aspects of chemical coevolution of plants and
insects in response to their interactions. We have cataloged plant metabolites, their
role in insect response, and the modulation of their interplay due to the evolution of
chemicals.
2
Plant Metabolites Involved in Establishment of Interaction
with Insects
Plant-insect relationship is a bidirectional process. For instance, upon insect feeding,
plants elicit specific defense response against them. In order to trigger insect-specific
defense, plants need to differentiate between physical injury and insect feeding.
It has been reported that insect’s oral secretion or oviposition fluid contain
specific active compounds called elicitors. These are sensed by plants and are
responsible for the activation of downstream signaling cascades related to defense
[7]. Also in contradiction, oral secretions have been seen to suppress plant defense
machinery [8].
2 Plant-Insect Interaction: The Saga of Molecular Coevolution
21
Origin of species.” He states that these plant-insect interactions could date back to
the Devonian period (420 million years ago [Mya]), as plants established themselves
on land. Plant-insect interactions became prominent in the Carboniferous period
(250–320 Mya) which is characterized by the appearance of insect pollination and
continue to dominate even today [1]. These interactions have resulted in a vast
diversification of plant and insect species [2].
The first evidence of plant-insect interaction is that of pollinivory and goes as far
back to the early Permian era (298 Mya) [3]. Furthermore, the emergence of
angiosperms is followed by an immediate shortfall of insect diversity. This can be
attributed to the time taken by insects to adapt and start feeding on seeds and fruits.
The advent of terrestrial plants caused insects to develop mouthparts that assisted
them to feed on seeds and other plant parts. Nectar-consuming insects (Hymenoptera
and Lepidoptera) came into existence in the late Cretaceous period after the appearance of pollen and nectar-producing plants (early Cretaceous period) [2]. Thus,
plants and their composition have a great influence on insect evolution.
The key feature in the success of these interactions is the adaptability of plants
and insects to generate diverse chemical compounds and utilize them for their
survival. The various chemicals synthesized by plants attract insects for pollination
or parasites for pest infestation. In addition, the arena of plant chemicals also acted as
defense compounds against herbivorous insects [4]. Depending on the level and type
of insect attack, plants modulated the production and distribution of these defense
metabolites. In response to this, insects developed functional survival tactics like
sequestration, detoxification, and repellence to combat negative or toxic effects of
defensive secondary metabolites [5]. The stress of toxic metabolites on insects
induced selection pressure that led to the emergence of resistance to phytochemicals.
Thus, mutualistic coevolution turned into a molecular warfare that resulted in the
generation of vast diversity in plant secondary metabolites [6] (Fig. 1).
Here, we are discussing various aspects of chemical coevolution of plants and
insects in response to their interactions. We have cataloged plant metabolites, their
role in insect response, and the modulation of their interplay due to the evolution of
chemicals.
2
Plant Metabolites Involved in Establishment of Interaction
with Insects
Plant-insect relationship is a bidirectional process. For instance, upon insect feeding,
plants elicit specific defense response against them. In order to trigger insect-specific
defense, plants need to differentiate between physical injury and insect feeding.
It has been reported that insect’s oral secretion or oviposition fluid contain
specific active compounds called elicitors. These are sensed by plants and are
responsible for the activation of downstream signaling cascades related to defense
[7]. Also in contradiction, oral secretions have been seen to suppress plant defense
machinery [8].
2 Plant-Insect Interaction: The Saga of Molecular Coevolution
21