Major Pests and Pest Management Strategies in the Sweet Pepper (Capsicum annuum)

Abstract

Sweet peppers (Capsicum annuum) (Solanaceae) fruits have been used as a food ingredient in Peru for more than 8,000 years. Then gradually, the plant has been cultivated in several countries worldwide. The fruits of the plant can be added to soups and stews as spices. These were reported to treat fevers, seasickness, muscle sprains, or soreness. Thrips, whiteflies, mites, and aphids were critical pests in sweet peppers. Therefore, effectively managing this important fruit to improve its yields and quality is very important. Pesticides have harmful effects on the environment and health of people. Therefore, alternative pest management strategies become more advisable to control pests of sweet pepper. These strategies including intercropping of sweet pepper with other plants, oviposition deterrents, natural enemy release, use of resistant cultivars, and eliciting plant defenses are implemented as environment-friendly control methods.

1. Introduction

Sweet pepper (C. annuum L.) and tomato crops occupy most of the area among protected species around the world. Pepper cultivation is almost entirely carried out in open fields; however, the extension of protected, greenhouse-cultivated peppers has intensively increased [1]. Sweet pepper is one of the very important crops worldwide. C. annuum includes hot as well as sweet pepper varieties. The world's main pepper-producing countries include China, Mexico, and Turkey, with over 17.4, 2.7, and 2.5 million pepper tons in 2016, respectively [2].

Other European countries and Canada are important producers of greenhouse peppers, with 135 million kg of peppers grown where yield is ≤12 t/ha, and sweet pepper is subject to several pests [3], such as beetles [4], caterpillars [5], aphids [6], and thrips [7]. Alternative control methods of pests to exclusively use of insecticides and integrated pest management (IPM) such as cultural, biological, and chemical treatments were used to manage sweet pepper pests [3].

2. Major pests of sweet pepper in green house

Sweet pepper is susceptible to attacks by several pests, which reduces fruit quality and yield. When insects and mites attack sweet pepper, both direct and indirect damages occur [3, 8]. The indirect damage is caused by pests when they transmit viruses, while the direct damage is those occurring when pests themselves cause damage to different parts of the plants. Instead of controlling pests with insecticides, integrated pest management strategies, especially those based on biological control methods, have been used effectively for several years worldwide to control pests of sweet pepper. Sweet pepper is one of the highly attractive crops to pests and pathogens. Those pests affecting pepper crops can differ based on geographic area and cropping system such as open field or greenhouse, and conventional or organic farming.

2.1 Arthropod pests

2.1.1 Thrips

Thrips are the number one pest of greenhouse crops in different climatic regions mainly due to their polyphagous diet and their ability to rapidly develop resistance to commercially available insecticides. Thrips cause significant damage, such as feeding and ovipositing on pepper leaves, fruit, and flowers, leading to decreased quality and marketability of fruits. The most known damaging thrip species include the western flower thrips, Frankliniella occidentalis, Thrips tabaci Lindeman, and Thrips palmi Karny [9]. Another thrip attacking Capsicum species is Scirtothrips dorsalis Hood. Thrips usually like closed areas such as the flowers, under the calyx of fruit and young leaves, which make them difficult to control with insecticides [3].

2.1.2 Whiteflies

Two principal whiteflies are reported to attack sweet pepper: the greenhouse whitefly, Trialeurodes vaporariorum (Westwood), and Bemisia tabaci. In some European regions, such as Spain, B. tabaci is the major pest of peppers [10].

Adult whiteflies and nymphal whiteflies feed on the vascular tissue in plants (phloem), causing direct damage. On the other hand, indirect damage results from virus transmission by adults and sooty mold, which develops on their excreted honeydew [11, 12].

2.1.3 Mites

2.1.3.1 Spider mites

The two-spotted spider mite (Tetranychus urticae, Koch) and the carmine spider mite (T. cinnabarinus, Boisduval) were reported as the important pests of pepper worldwide. These mites cause whitish or yellowish stippling in the upper leaf surfaces and produce silk webbing [13].

2.1.3.2 Broad mites

The broad mite is one of the notorious pepper pests in different regions of the world [14]. It mainly causes damage to different parts of sweet pepper at the younger stage and is difficult to manage due to its small size. It usually feeds on the lower leaf surface and distorts flowers and blistering of fruits. When the broad mite gains access to enter a greenhouse, it can spread rapidly, resulting in high economic losses [3].

2.1.4 Aphids

Aphids are generally important pests of sweet pepper, especially in open fields compared with those covered. The most critical aphid is the green peach aphid, Myzus persicae (Sulzer), which causes direct damage to leaves by the secretion of phytotoxins into the plants [15]. In general, the damage caused by aphids is indirect, such as sooty molds growing on secreted honeydew and transmission of potyviruses. Another aphid pest reported in subtropical-covered peppers is Aphis gossypii (Glover) [16].

3. Pest management

Management strategies of greenhouse pests using chemicals were reported to result in several problems, such developments of resistance to chemicals by pests, and environmental and health problems are caused by those chemical pesticides [17]. The possibility of applying biological control programs to problems of greenhouse pests is highly recommended. Even though they will not completely solve the problems, they can reduce pest populations to an acceptable level. Biological control generally requires more time than pesticides to bring a pest population under an acceptable control level [18]. Biological control strategy such as releasing different predators and parasitoids was reported to be environmentally friendly production method of sweet pepper. Applying the biological control program resulted in a high yield of sweet pepper production (35.06%) compared with the control [17]. In this book chapter, various pest control methods are reviewed.

3.1 Polyethylene plastic cladding material

The most commonly used material for greenhouse covering is polyethylene screening plastic, which has an ultraviolet-absorbing characteristic. The material was prepared by adding a specific UV-absorbing compound to raw polyethylene, which makes the plastic material that can stop the transmission of 95% of the UV light (200–380 nm) and transmits 80% of visible light (380–700 nm) [19]. The behaviors of insects can be affected by the modification of UV light. Light at 360–400 nm activates whiteflies (T. vaporariorum) to walk and fly [20]. Similarly, the effects of UV-absorbing plastics on thrips, F. occidentalis, have also been reported as host-finding behavior is disrupted [21]. Reduction in reproduction in aphids by deactivation of its flying behavior was reported. For example, reproduction in M. persicae is significantly reduced in a greenhouse covered with UV-absorbent plastic [15].

3.2 Predators

3.2.1 Phytoseiidae (Acari)

Many phytoseiid mites are predatory, and several species have been developed as biological control strategies [3]. McMurtry and Croft [22] classify several phytoseiid mites based on their feeding behaviors. Type I species include Phytoseiulus spp., mites that are well known as predators of webbing spider mites. Type II mite species include Neoseiulus californicus (McGregor) and N. fallacis (Garman), which feed spider mites and others. Type III species, for example, N. barkeri (Hughes), N. cucumeris (Oudemans), and Iphiseius degenerans (Berlese), are generalists that often prefer prey other than spider mites (in whose webbing they may become entangled) and thrips [3].

3.2.2 Diptera

Aphidoletes aphidimyza is a predatory cecidomyiid that has been used to control aphids [23, 24]. A. aphidimyza in the adult stage are important for hunting aphids. They are released in the greenhouse together with the parasitoid A. colemani Viereck for a better effect. Additionally, their larvae were reported to attack several species of aphids. A method of effective utilization in pepper fields in greenhouses was highlighted [25].

3.2.3 Heteroptera

Weintraub [3] reviewed many species of the anthocorid bug, Orius, which have been evaluated for controlling thrips on protected sweet pepper crops. Both adults and nymphs can frequently be found in flowers, a location that is favorable for thrips. Additionally, unlike predatory mites, Orius spp. attack both adult and immature thrips. Dissevelt et al. [26] reported the potential of O. niger, O. majusculu, and O. laevigatu, O. insidiosus and O. albidipennis to control thrips on pepper.

3.2.4 Neuroptera

Chrysoperla carnea (Stephans) is a generalist predator that appears in open fields and is difficult to rear commercially because it is highly carnivorous. There was a report [27] on controlling the aphid M. persicae on peppers by C. carnea.

3.2.5 Mirid predator

Predatory mirid bugs (Hemiptera: Miridae) were reported as biocontrol agents in sweet pepper [28, 29]. In addition to their agricultural uses as predators, mirid predators can induce plant defenses by phytophagy [30]. The punctures caused by mirid plant feeding induced the release of a mixture of volatile organic compounds (VOCs), namely green leaf volatiles [((Z)-3-hexenyl acetate, (Z)-3-hexenyl propanoate, (Z)-3-hexenyl butanoate, (Z)-3-hexenyl 3-methylbutanoate, and (Z)-3-hexenyl benzoate) and their common precursor (Z)-3-hexenol], methyl salicylate, and octyl acetate. Octyl acetate was detected in M. pygmaeus-punctured plants, which repelled the herbivore pests F. occidentalis and B. tabaci and simultaneously attracted the whitefly parasitoid Encarsia Formosa [30].

3.2.6 Aphidophagous hoverflies

Moerkens et al. [31] investigated the potential of hoverflies Eupeodes corollae and Sphaerophoria rueppellii to manage foxglove aphid Aulacorthum solani in sweet pepper. In a semi-field study, aphid numbers were significantly lower in the E. corollae and S. rueppellii treatments than in control. The fruit yield and seed set were also increased for E. corollae and S. rueppellii.

3.3 Parasitoids

Most parasitoids developed for biological control belong to the family Aphelinidae. These parasitoids are tiny wasps and have been used to control the whitefly [32]. For instance, Encarsia formosa is a parasitoid used worldwide for the biological control of whiteflies attacking various vegetables such as sweet pepper cultivated in greenhouses. It lays eggs into hosts and causes a reduction of hosts. Uses of E. formosa are well known for controlling whiteflies because of the following factors. Whitefly population growth is reduced when E. formosa’s intrinsic rate of increase is greater than the host’s intrinsic in the presence of parasitoids. This situation has resulted when host plants facilitate parasitoid searching and exhibit partial resistance to whitefly development. Additionally, giving-up time on infested leaves increases when hosts or host products are located, increasing the likelihood that parasitoids will encounter suitable hosts in a patch. It was also reported that spatial refuges for whiteflies from parasitoids exist in large greenhouses (greater than 1000 m²) and consequently promote stable host or parasitoid dynamics [32].

3.4 Entomopathogens

Entomopathogenic fungi are effective methods of controlling pests though it requires humid conditions to allow the propagules to penetrate the insect body, after which fungal development generally proceeds. A means of pathogen delivery is by using bees that were reported to be applicable for field crops [33, 34]. For instance, strains of Beauveria bassiana (Balsamo) Vuillemin have been shown to be virulent to F. occidentalis and T. tabaci [35, 36]. Bumble bees were used for pepper pollination and could distribute the B. bassiana conidia to flowers and leaves [37]. Since N. cucumeris is known to be unaffected by B. bassiana, [36], they have been reported to deliver inoculum for days or weeks without compromising other biological control methods.

3.5 Oviposition deterrents

Luteolin 7-O-β-D-apiofuranosyl-(1 2)-β-D-glucopyranoside was isolated from matured leaves of sweet pepper and identified as the ovipositional deterrent against Liriomyza trifolii (Burgess), the American serpentine leaf miner [38]. This insect species attacks C. annuum leaves in the young stage. The attack by this insect to leaves of the plant decreases as the plant becomes matured. This compound completely deterred L. trifolii females from laying their eggs on a host plant leaf treated at 4.90 g/cm² [38]. Additionally, phytol [(2E)-3,7,11,15-tetramethyl-2-hexadecen-1-ol] constituent of matured leaves of sweet pepper was also reported as an ovipositional deterrent against L. trifolii. Phytol [(2E)-3,7,11,15-tetramethyl-2-hexadecen-1-ol] completely deterred the females from laying their eggs on host plant leaves treated at 35.2 μg/cm². 4-aminobutanoic acid, (2S,4R)-4-hydroxy-1-methyl-2-pyrrolidine carboxylic acid, and 4-amino-1--D-ribofuranosyl-2(1H)-pyrimidinone were reported from the leaves of sweet pepper showed oviposition deterrence toward adult flies of L. trifolii from laying their eggs on kidney bean leaves (host plant) treated at 3.70, 16.60, and 6.45 g/cm², respectively [39].

3.6 Intercropping of sweet pepper with other plants

It was reported that monocropped pepper, such as pepper, intercropped with maize (Zea mays) or eggplant (Solanum melongena). Maize acted as a barrier crop for aphids (Aphis gossypii) and reduced virus infection on pepper in the first part of the cropping season [40, 41]. Eggplant was reported to act as a trap crop for aphids and reduced virus infection on pepper for a longer period than maize [40].

Additionally, Li et al. [42] reported intercropping rosemary with sweet pepper results in the population of three main pest species on sweet pepper. The significant pest population suppression and the absence of adverse effects on natural enemies in the sweet pepper/rosemary intercropping system show the potential of this strategy in the IPM framework. Consequently, intercropping sweet pepper increases yields of pepper intercropped with other crops.

3.7 Eliciting plant defenses in sweet pepper

The exposure of sweet pepper plants to HIPVs such as [(Z)-3-hexenol, (Z)-3-hexenyl acetate, (Z)-3-hexenyl propanoate, (Z)-3-hexenyl butanoate, hexyl butanoate, methyl salicylate, and methyl jasmonate] over 48 h activates the sweet pepper immune defense system against various pests [43]. The volatiles inducted the plant defenses due to the regulation of the jasmonic acid and salicylic acid signaling pathway. A principal sweet pepper pest is Frankliniella occidentalis, and Orius laevigatus is its main natural enemy. HIPV-exposed sweet pepper plants were investigated, and the results showed that only plants exposed to (Z)-3-hexenyl propanoate and methyl salicylate repelled F. occidentalis, whereas O. laevigatus showed a strong preference for plants exposed to (Z)-3-hexenol, (Z)-3-hexenyl propanoate, (Z)-3-hexenyl butanoate, methyl salicylate, and methyl jasmonate. In the related study, treatment of cotyledons of sweet pepper with 50 and 100 μM of jasmonic acid (JA) solution resulted in strong plant’s oviposition deterrence against the leaf miner L. trifolii [44]. These results demonstrate that HIPVs act as elicitors to sweet pepper plant defenses by enhancing defensive signaling pathways. Enhancing defensive signaling pathways is very important for integrating HIPVs-based approaches in sweet pepper pest management systems, which may provide a sustainable strategy to manage insect pests in horticultural plants.

3.8 Resistant cultivars

Several pepper accessions have been evaluated for thrips resistance, and significant differences in damage levels have been observed [45]. The difference between different accessions was found to be through tolerance. There were attempts to breed pepper plants for simultaneous resistance to arthropod vectors and pathogens though those attempts were not successful. Some pepper accessions were reported to be resistant to A. gossypii; however, these plants did not show resistance to the green peach aphid attack. Several commercial peppers exhibited strong resistance to M. persicae, as demonstrated by reduced damage to the plants [46]. Interestingly, some pepper cultivars exhibited tolerance to aphid-transmitted viruses [3].

3.9 Chemical control

Weintraub [3] reviewed that even insecticides considered acceptable for use along with some beneficial organisms. For instance, Spinosad that is prepared by fermentation of an actinomycete has been evaluated to control Western flower thrips (WFT) [47]. It was found that while Spinosad was effective against immature and adult WFT, it also showed low toxicity to Amblyseius cucumeris exposed to leaves 1 day after treatment. Spinosad exhibited moderate toxicity to Oriusinsidiosus 1 and 8 days after treatment and high toxicity to Encarsia formosa up to 28 days after application [47].

4. Conclusion

The major pests of sweet pepper are Arthropod pests such as thrips, whiteflies, mites, and aphids. These pests cause enormous damage on sweet pepper by feeding and ovipositing on pepper leaves, fruit, and flowers, which lead to decreased quality and marketability of fruits. Some of the various pest management strategies used to manage these pests are physical technique (polyethylene plastic cladding materials), biological control methods such as the use of predators, parasitoids, and entomopathogens, oviposition deterrents, intercropping with other plants, eliciting plant defenses-resistant cultivars, and chemical control. Utilizing a biological control strategy by releasing different predators and parasitoids resulted in an environmentally friendly method of controlling sweet pepper greenhouse production.

Acknowledgments

Adama Science and Technology University supported the author with the grant, ASTU/AS-R/003/2020. I thank the World Academy of Sciences (TWAS) and the United Nations Educational, Scientific, and Cultural Organization (UNESCO) for funds allocated to the author under the TWAS Research Grant RGA No. 20-274 RG/CHE/AF/AC_G – FR3240314163.

Conflict of interest

The author declares that they have no conflicts of interest.