**5.8 Botanicals**

Keeping in view the discouraging aspects of synthetic pesticides such as toxicity, non-biodegradability, costlier, residual effects, and many other harmful effects on plants, humans, and other animals urged experts to look for an alternative powerful, economically viable, and eco-friendly approach. One such suitable method is the use of plant volatile organic compounds that possess insecticidal properties. Some plants are bestowed by nature with several bioactive organic chemicals or phytochemicals, having a defensive role against insect pests. These organic bioactive compounds provide an odor for the repellence of insects and are volatile in nature, hence commonly referred to as plant volatile organic compounds (PVOC). Plant volatiles is the most viable options for effective control measures against various pests, having no or fewer threats to the environment [37, 38]. Secondary metabolites of plants such as terpenoids, phenols, and alkaloids [39], act as attractants or repellents, influences the growth and development, ecdysis, fertility, behavior, mating, adult emergence, and plays an important role in crop protection [40]. Especially developing countries are using botanicals to reduce the infestation level [41]. Phytochemicals can be used in the form of aqueous or solvent extracts, powders, slurries, volatiles, and oils or shredded segments [38, 42]. Hence, botanicals hold promise as an alternative to synthetic insecticides to lessen the negative impact of the pesticide on the environment. Botanicals, as well as their active ingredients and the target pest upon which these are used, are listed in **Table 1** as enlisted by Singh et al. [43].

Botanicals or phytochemicals have a different mode of action on insect pests and consist of aldehydes, ketones, alcohols, alkanes, and terpenoids. Their effect on pests in several manners are described below:

*Growth and development regulators:* Phytochemicals are known to change the physiology and behavior of insects by affecting the growth, development, and metamorphosis of insects. Reduction in weight of larvae, pupa, and adult, prolonged larval and pupal periods are also some irreversible changes caused by botanical extracts [44]. Growth and development inhibition of C. maculatus is happened on applying the essential oil extracted from the *Cymbopogon schoenanthus* of the Poaceae family [45]. Botanicals have such a power of action that they can also inhibit the development of eggs and other immature stages residing inside the grain kernels. Aqueous extract of *Xanthium strumarium* leaf was reported to show toxicity, repellency, inhibition of fecundity and adult emergence of the pests, and grains as well as cereals protection against C. chinensis [46].

*Hormone regulator:* Plant volatiles has juvenile effects as well, i.e., they are playing an active role in the hormonal regulation of insect pests. Extracts of water hyacinth contain a juvenile hormone analog that changes the reproductive behavior and causes abnormal molting and metamorphosis of stored grain pests [47]. *Solasodine* could inhibit molting and induce several morphogenic abnormalities in the larvae of *T. confusum* at the concentration of 1 μg/μl.

#### *Postharvest Technology - Recent Advances, New Perspectives and Applications*


*Stored Grain Pests and Current Advances for Their Management DOI: http://dx.doi.org/10.5772/intechopen.101503*


#### **Table 1.**

*Plant volatile organic compounds used against stored grain pests.*

*Oviposition deterrent:* Chemicals that prevent or simply avoid insects from the process of oviposition is referred to as oviposition deterrent. Oviposition deterrents help to reduce the infestation level and offer the first line of defense against insect pests. An illusion is created by the plant volatiles to the gravid female pests, as these are involved in partially or completely preventing oviposition as well as the emergence of larvae from the laid eggs on stored grains [48, 49]. Garlic oil [50], 1,8 Cineole from Lamiaceae family [51], essential oils of *Eucalyptus citriodora*, *E. globulus*, *E. stageriana* [52], *Trachyspermum Ammi*, *Antheum graveolens*, *Nigella sativa*, are the oviposition deterrents, thereby reducing the viability of eggs and emergence of *Zabrotes subfaciatus*, *T. castaneum*, and *C. maculatus*. Finely powdered and dried leaves of *Ocimum* can completely suppress the oviposition of *Zabrotes subfascial* at 2%W/W, with an EC50, of 0.45% W/W [53]. The powdered form of *Chenopodium ambrosioides*, *Tagetesminuta*, *A. indica*, and *C. lusitanica*, applied at the rate of 1.5 kg/100 kg of *Phaseolus vulgaris*, was found to be the most effective in the mortality of Z. subfascial and A. objects [54]. Some phytochemicals obtained from *Laurus nobilis* and *Rosmarinus officinale* are causing egg mortality [55].

*Repellent activity:* Chemicals that protect stored grains, plants, or other products from insect damage by making the grains unattractive, offensive, or unpalatable to pests are commonly referred to as repellents. Repellents are especially more functional against various types of beetles, causing them to flee from the treated stored products. Compounds such as germacrol, pulegol, and α-terpineol isolated from *Baccharis salicifolia* and ar-turmerone isolated from *Curcuma longa* are potent repellents against *T. castaneum* and *S. zeamais* [56, 57]. Infestation by *T. castaneum* can be effectively controlled by different solvent extracts, acting as repellents, obtained

from *Sphaeranthus indicus*, *Tephrosia purpurea*, *Prosopis juliflora*, *Cymbopogon flexuous, Cymbopogon winterianus*, and *C. martini*. Ethanolic extract of Acorus calamus is an active constituent Z-asarone, which acts as a strong repellent against *S. zeamais* [58]. Repellent used against *C. chinensis* is an essential oil obtained from *Callistemon lanceolatus* [59].

*Antifeedant:* Chemical substance that disrupts the feeding behavior of insect pests by making the treated stored grains unpalatable are referred to as antifeedant. The presence of certain chemicals in plants acts as a defensive mechanism to them. Antifeedants are eco-friendly, without ever disturbing the ecological balance, and do not kill the target but only prevent them from infestation. The deleterious effect of azadirachtin and neem seed extracts of *A. indica*, in antifeedant against various pests, is highly appreciable. Some essential oils acting as antifeedants are obtained from *Gaultheria procumbens*, against *S. oryzae* and *R. dominica* [60]. Some flavonoid compounds acting as antifeedants are Isoglabratephrin, −glabratephrin, tephroapollin-F, and lanceolatin-A, isolated from *Tephrosia apollinea*, against *T. castaneum*, *S. oryzae*, and *R. dominica*.

*Ovicidal effects:* Substances having the potential to kill eggs are considered to have ovicidal effects. This ovicidal property is also present in certain plants and is of great importance in the management of insect pests [61]. Plant volatiles sprayed on the stored grains could tremendously reduce the number of adult emergences because of toxicity or due to change in surface tension within the eggs [62]. Flavonoids isolated from *Calotropis Procera* provide 100% progeny suppression to the eggs of *C. chinensis* at 10 mg/ml concentration. An essential oil obtained from Anethum Sowa also shows ovicidal effects on eggs of *C. maculatus* [63]. From *Mentha ravens*, *Cinnamomum zeylanicum*, *Elettaria cardamomum*, *Syzygium aromaticum*, and *A. indica*, essential oils are extracted which has also ovicidal activity on the eggs of *T. castaneum* [64].

*Chemosterilents:* Substances that deprive insects of their ability to reproduce are known as Chemosterilents. Chemosterilents produce irreversible sterility without affecting the behavior of pests. These chemicals affect almost all stages of insect pests where eggs may not be oviposited, eggs not hatching, no pupation of larvae, and no adult emergence from these pupae [59]. Compounds possessing chemosterilent properties are asarone and 1,3,7-trimethylxanthine used against *C. chinensis* [65].

*Behavioral disturbance:* Behavioral changes are also induced by the plant volatiles, which can either stimulate or reduce insect mobility, and other physiological changes [66]. Some essential oils are known to inhibit acetylcholinesterase enzymes on insects' nervous system and also GABAergic is disrupted [67]. Essential oils of clove and Cinnamomum used on *S. zeamais* effects their locomotory and respiratory processes [68].

#### **5.9 Pheromonal approach**

Pheromones are ectohormones released by either male or female partners to change each other's behavior. Pheromones are now commercially available for around 20 species of stored grain pests [69]. Pheromones for *P. interpunctella*, *Lasioderma serricorne*, *T. castaneum, T. confusum, Trogoderma* variabile, are used frequently. These pheromones are placed inside suitable traps for their smooth release and maximum attraction as well as trapping processes. Proper installation of pheromone baited sticky traps within a building, granaries, and other flat landing sites plays an important role in the efficacy of pheromones used [70]. Sticky traps are placed on the sides of containers or the flat surface to capture crawling insects especially beetles, that eventually become stuck to the trapping surface. A trap with horizontal layers of corrugated cardboard was developed by [71] for

beetles that walked through the tunnels of corrugations to reach a cup of oil into which they fell and suffocated.
