Introduction

Insects share antagonism, commensalism, and mutualism relationships

with plants and all these interactions play a major role in food production in

agriculture, horticulture, and forestry (Schoonhoven et al., 2005). This

interaction happens on the whole-plant and community levels and on the

morphological and cellular levels of insects and plants (Sharma et al., 2014).

Primarily, only 9 out of 30 orders are phytophagous (Gullan and Cranston,

2000). Nonetheless, members of Orthoptera, Hemiptera, Hymenoptera, Diptera,

Lepidoptera, Coleoptera, Thysanoptera, Phasmida, Trichoptera, Plecoptera, and

Ephemeroptera, Acarina (Arachnida) are plant feeding. Phytophagous insects

seem to show a certain degree of coevolution with plants and exhibit two modes

of co-evolution: specific and diffuse (Gullan and Cranston, 2000).

Phytophagous insects have chewing and biting, sap-sucking, and siphoning

types of mouth parts. Insects feed on plants to consume primary metabolites

(e.g. carbohydrates, lipids, and proteins) for their growth and development.

Plants also produce a high diversity of secondary metabolites (e.g. alkaloids,

terpenoids, and phenolics) and insects become continuously challenged with

counter mechanisms to detoxify plant defense mechanisms (Nishida, 2014).

Insects are polyphagous, oligophagous, and monophagous due to variation in

their requirement for primary metabolites for food, reproduction, habitat, and

microclimate (Gullan and Cranston, 2000; Sharma et al., 2015).

Insect and plant interactions become complicated and necessary since plants

serve as food for insects but at the same time have an array of secondary

metabolites which can function as phago-stimulant and deterrent, and they also

get sequestered by insects and used for their own defense mechanisms. A

plant’s secondary metabolites are also used in communication with insects.

Several secondary metabolites also enable the management of insect pests

through the incorporation of these compounds in attract-and-kill strategies and

push-and-pull strategies (Nishida, 2014; Khan et al., 2016). Insect attack also

induces volatile production in plants, which, in turn, attracts the predators and

parasites of insects. In short, from finding the plant to feed and lay eggs to

coping with the plant’s secondary metabolites, both partners in insect–plant

interaction show an array of strategies that benefit from this interaction.

Insects’ sensory structures enable them to find the host plant which mainly

includes optical and odor clues. However, optical clues for insects remain fairly

constant since light intensity is the only factor which influences the optical

clues. In contrast, chemical clues or odorous clues vary immensely due to

variation in wind speed, temperature, and plant’s physiological state especially

when the plants are under attack. Insects’ endocrine system also plays an

integral part in host plant selection. Choice of annual and perennial plants or a

particular developmental stage depends on the insect’s physiological

requirement. Hormones and pheromones required for molting, morphism,

 diapause, maturation, and mating in insects depend on the quantity and quality

of host plant (Reddy and Guerrero, 2010).

Insect Plant Key points of Interaction

Production of symbiotic fungus, Leucoagaricus

Ant, Atta Mexicana Unspecified
gongylophorus which detoxifies the plant.

Striped Cucumber Cucurbits such as Presence of striped cucumber beetle reduces

Beetle, Acalymma vittatum cucumber pollinators

Soil pH affects pre-reproductive, reproductive,

Aphid, Aphis craccivora Faba bean, Vicia faba
post-reproductive and pre-viviparity periods

Cabbage, Brassica Reduced solute accumulation in drought-stressed

Aphid, Myzus persicae
oleraceae cabbage

HIPVs are used by female parasitoids in locating

Cotesia glomerata unspecified
hosts.

The aphid, Lipaphis erysimi,

Different mouthparts used in attacking plants
and a lepidopteran, Plutella unspecified
affect concentrations of phenols in the plant
xylostella

Table 1. Summary and key points of plant-insect interactions.

Symbionts play a major role in allowing phytophagous insects to feed on

plants with several secondary metabolites which can be harmful to insects.

Endosymbionts live in insects extracellularly and intracellularly and improve

the capacity of insects to digest food, supply essential amino acids which

otherwise cannot be obtained by insects, and detoxify plant’s allelochemicals

which can be harmful to insects (Moran, 2002). Along with endosymbionts, for

detoxification of secondary metabolites of plants, insects excrete them

physiologically and also detoxify the metabolites with the help of enzymes. The

enzymatic detoxification happens before food ingestion, that is, through salivary

proteins and also during digestion (Sharma et al., 2014).

 On one hand, insects possess various features to successfully consume

plants, and on the other hand, plants comprise several characteristics to avoid

getting attacked by insects. Plants imply ‘phenological escape’ to avoid getting

attacked by specific insects (Visser and Holleman, 2001); plants imply

secondary metabolites which can be toxic and digestibility reducer to insects,

emit insects- induced volatiles which attract natural enemies of insects can

increase nectar secretion to provide food to natural enemies (Heil et al., 2001);

and has morphological traits such as surface structure and trichomes. The

evolution of plants transformed the terrestrial environment into a highly

valuable resource for the herbivore community. In natural ecosystems, plants

and insects are just some of the living organisms that are continuously

interacting in a complex way. These two organisms are intimately associated

since insects have several beneficial activities including defense and pollination

while plants provide shelter, oviposition sites and food, the three main factors

requested for insect proliferation (Panda and Khush, 2005). On the other hand,

depending on the intensity of insect attack, herbivores might be extremely

harmful to plants leading them to death.

Plant-insect interaction is a dynamic system, subjected to continual variation

and change. In order to reduce insect attack, plants developed different defense

mechanisms including chemical and physical barriers such as the induction of

defensive proteins, volatiles that attract predators of the insect herbivoresc

secondary metabolites and trichome density. In parallel, insects developed

strategies to overcome plant barriers such as detoxification of toxic compounds,

avoidance mechanisms, sequestration of poison and alteration of gene

expression pattern (Silva et al., 2001)

Insect physiological changes during insect-plant interaction

The interactions between phytophagous insects and their host plants

result from a long and continuous evolutionary process (Beran and Petschenka,

2022). Such ecological relationships led to an extraordinary diversity of insects

and shaped their complex physiological systems (Wheat et al., 2007). The

impacts of host plants on the physiology of herbivorous insects have

increasingly become a paramount focus that should not be ignored. Chemical

compounds’ composition of plants have not only significant variations in the

inter/intra species aspect but also show spatiotemporal variations in different

developmental stages and tissue types, or under changeable environments in

nature, which lead to the resource assimilation and fitness challenges of insects

(Delucia et al., 2012; Brütting et al., 2017). These close interations with plants

affect the ecological plasticity of the performance of insect herbivores (Barker

et al., 2019). Currently, in-depth exploration of the host plants’ effect on insects

has become a research hotspot of insect physiology, however to test the highly

complex hypothesis can be difficult. The current Research Topic aimed to

highlight the recent developments on 1) how physiological changes occurred in

herbivores during their interaction with host plants, 2) how these physiological

changes in insects could be affected by other biotic factors.

The interaction between the diamond back moth (DBM), Plutella

xylostella (Linnaeus) (Lepidoptera: Plutellidae), and the crucifer plants is one of

the most well-known models in chemical ecology. It was established that the β-

glucosidases (myrosinase) and glucosinolates (GSLs) are stored in distinct

subcellular compartments in plants, and the contact between them due to

herbivory damage can rapidly produce a group of toxic aglycones, such as

isothiocyanates (ITCs) (Textor and Gershenzon, 2009). These sulfur-containing

aglycones can be deterrent to many insect pests but not to DBM, since DBM

can hydrolyze the glucosinolates into desulfur-glucosinolates by using

glucosinolate sulfatases (GSSs) (Winde and Wittstock, 2011). Chen et al.

identified 13 glycoside hydrolase family 1 (GH1) genes in DBM. Among them,

the midgut-specific gene Px008848 is induced by feeding on the host plant. In

vitro expression of Px008848 protein showed β-glucosidase activity, and

Arabidopsis thaliana leaves treated with this protein can significantly reduce the

survival of DBM larvae. Meanwhile, knocking out this gene by CRISPR/Cas9

enhanced the survival rate of this insect on A. thaliana, indicating that this gene

might be involved in the interaction between DBM and their host plants; and

consequently illuminating our understanding of the evolutionary function of this

gene family in the insect-plant interaction.

 Insects rely on metabolic enzymes to detoxify the secondary metabolites

in the host plant tissues they consume. Glutathione-S-transferases (GSTs) are

among herbivores’ most well-studied metabolic enzymes (Rane et al., 2019).

Venthur et al. identified 22 GSTs in the greater wax moth, Galleria mellonella

(Linnaeus) (Lepidoptera: Pyralidae), a global pest for beehives. Treating the

larvae with root extract of Berberis microphylla G. Forst (Ranunculales:

Berberidaceae), as well as the alkaloids from these extracts, the alkaloids

berberine and palmatine were found to induce the accumulation of transcripts

for some of these GSTs. The protein structure prediction suggested putative

interactions between these GSTs and chemicals.

Pathogens can affect the performance of vector insects either by direct

infection or indirectly changing host plants’ physiological status (Colvin et al.,

2006). Citrus Huanglongbing disease is a destructive disease caused by the

pathogen Candidatus Liberibacter asiaticus (CLas), and the Asian citrus psyllid

Diaphorina citri Kuwayama (Hemiptera: Liviidae) is a key vector for this

pathogen (Galdeano et al., 2020). Zhang et al. found that CLas can change the

abundance, composition and utilization efficiency of different amino acids in

citrus host plants, thus affecting the construction of amino acids in nymphs and

adults of D. citri, which could potentially affect their transmission of CLas. This

study provided relevant evidence that pathogen-mediated changes of primary

metabolites in plants can affect the performance of their insect vector.

Conclusions
Agriculture and insects have beneficial and detrimental associations

These multifaceted interactions can involve antagonistic, mutualistic, or

commensalistic relationships between insects and plants. Therefore, managing

agroecosystems must prioritize incorporating conservation measures, such as

ecologically sound methods of pest insect control, as these approaches will

provide advantages for both agriculture and insect preservation. Land-use

alterations, such as deforestation and the expansion of agricultural areas, can

significantly influence these interactions. These alterations may also impact the

diversity and abundance of plants and insects, influencing the type and amount

of food available to insects and their ability to consume crops. Plants are at the

heart of a complex web of multitrophic interactions that regulate ecological

dynamics at multiple levels. Understanding these interactions and their

regulatory mechanisms is essential for developing sustainable agricultural

practices that enhance crop health and productivity while maintaining

ecological balance. By integrating ecological principles into selective breeding

and crop management, we can better navigate the trade-offs between yield,

taste, and pest resistance, ultimately leading to more resilient and sustainable

agricultural systems. In recent years, climate change has continued influencing

plant-insect interactions in agroecosystems. Rising temperatures and increasing

levels of carbon dioxide in the atmosphere can significantly affect the chemical

composition of plant tissues, such as the levels of sugars, amino acids, and
secondary metabolites. This can affect the quality and suitability of these plants

as food for insects. Increased levels of carbon dioxide in the atmosphere can

also affect the chemical composition of plant tissues, making them less

nutritious and suitable as food for insects. Variations in temperature and

precipitation can also change the levels of protective compounds produced by

plants, affecting insects’ ability to feed and reproduce. Thus, improved plant-

insect interactions may result from encouraging habitat restoration by creating

and restoring habitats for beneficial insects, such as by planting native flowering

plants or providing bees with places to nest. This implies that the interaction

between plants and insects can be improved by promoting conservation and

bolstering agroecosystem conservation practices.

The continuing effect of climate change and other human-caused factors

on ecosystems necessitates the continued investigation of insect-plant

interactions, which is crucial for both agricultural and ecological sciences.

Gaining a comprehensive understanding of these interactions is of utmost

importance in formulating effective and long-lasting pest control methods in

agriculture and accurately forecasting the potential impact of environmental

changes on ecosystems.

Recommendation
 i. Research should also investigate how specific insect infestations

influence the shifts in plant microbiomes and the subsequent effects on

soil microbial communities, focusing on identifying key microbial

species that mediate plant resistance or susceptibility to herbivory.

ii. Besides, there is a need to conduct detailed studies on how different types

of herbivores affect nutrient release, soil fertility, and competition

between plants and soil microorganisms in various agroecosystems,

including the role of plant litter quality and quantity.

iii. Moreover, assessing the cascading effects of changes in insect abundance

and composition due to plant-insect interactions on bird and mammal

populations aims to understand the broader ecological impacts and inform

biodiversity conservation strategies.

iv. Lastly, there is a need to develop and test innovative soil and pest

management practices that enhance nutrient diversity and cycling, aiming

to promote sustainable agroecosystems. This could include specific crop

rotations, organic amendments, or beneficial microbial inoculants to

mitigate the negative impacts of insect herbivory on soil health and crop

productivity.