The role of baculoviruses in controlling insect pests: A review

Abstract

Baculovirus play a major role in the control of insect pests that reduce the negative effect of synthetic insecticides on non-target groups and latter improve the integrated pest management for sustainable, effective and economical insect pest management practices. However, its impact on the control of insect pests is not well recognized. This review assesses the role of baculoviruses in controlling insect pests and indicates future research areas. Many viruses occur naturally, but some are produced commercially. Baculovirus is one of the microbial biopesticides that play an important role in providing pest management tools in areas where pesticide resistance, niche markets, and environmental concerns reduce the use of synthetic insecticide products. The Nucleopolyhedrovirus and Granulovirus are the two major groups of baculoviruses used as microbial biocontrol agents. Baculoviruses are important for insect pest management, reducing insecticide resistance and host specificity. On the other hand, the high specificity of baculoviruses is reported as a limitation for agricultural uses, since growers may need one product to use against a different pest. However, virologists have been working on increase the effectiveness of viral biocontrol agents through genetic engineering. Genetic engineering plays a vital role to improve insect killing rates, infectivity, and ultraviolet resistance to enhance viruses for insect control. Recombinant viruses have been engineered with the goal of shortening the time required for infection to kill insect pests. Still now, commercialization of baculoviruses is a major challenge, therefore researchers and stakeholders give attention to optimize massive production of baculoviruses for integrated insect pest management.

Keywords:

• baculoviruses
• biopesticides
• entomopathogenic viruses
• genetic modification

Public interest statement

Insects and other arthropods are susceptible to baculoviruses, which are diseases. Similar to some human viruses, they are often quite small (less than a thousandth of a millimetre in diameter) and predominantly made of double-stranded DNA, which codes for the genes necessary for virus establishment and reproduction. Baculoviruses, which are naturally occurring viruses with the ability to infect insects, are utilized in biocontrol. When one of these eligible insect hosts consumes these naturally occurring infections, the pathogens proliferate in the insect’s gut cells, resulting in illness and death. At currently, only in vivo methods have been used for the commercial production of baculoviruses. These methods include injecting the virus to the host insect in the field and gathering sick or dead larvae, as well as growing the target insect in a lab on an artificial diet.

1. Introduction

In most developing countries, the use of synthetic insecticides has been the major approach in modern agriculture for controlling insect pests on different crops (Hajjar et al., 2023). Chemical control is an effective and quick method for reducing pest populations, and farmers obtain spectacular results within a short period (Ramlee, 2015). However, the application of conventional insecticides can have a negative effect on human health, the environment, and other living organisms (Gangwar et al., 2021). Many unacceptable problems caused by the overdependence and indiscriminate use of pesticides lead to environmental contamination, loss of biodiversity, development of insecticide-resistant pest populations, resurgence, outbreaks of secondary pests, increases in inputs of chemicals and toxicological hazards due to the accumulation of pesticide residues in the food chain (Ananthi et al., 2015).

There is an alternative, ecologically healthy method of pest management that uses organisms to reduce the population density of insect pests to solve these issues. Microbial pathogens are widely used as biopesticides because they are simple to produce and apply, widely accepted, persistent, economically viable, and environmentally friendly (Ayilara et al., 2023). In many countries, numerous species of insect pathogenic microorganisms have been exploited as biopesticides, and some species have been developed into commercial formulations that are being used (Chattopadhyay et al., 2017). Several microbial applications are widely known in solving major agricultural insect problems and environmental issues (Higa & Parr, 1994).

Bio pesticides are very effective in agricultural pest control without causing serious harm to environmental conditions (Leng et al., 2011). Because of their inherent characteristics, one potential management strategy for insect pests is the use of entomopathogenic viruses, which appear to be among the promising bio pesticides (Georgis et al., 2006). Several viruses belonging to 18 different families are known to infect invertebrates and insects (Dacheux et al., 2014). However, baculoviruses comprising nuclear polyhedrosis virus (NPV) and granulosis virus (GV) have been successfully used as insect pathogens due to their high virulence and specificity (Raj et al., 2022). Contrarily, controlling how baculoviruses behave is a crucial element in integrated pest management strategies for crop protection (Rajarathinam et al., 2023). Furthermore, it is recognized as a successful, environmentally friendly, technically sound, financially feasible, and socially acceptable form of pest management (Kiss, 2020). Hence, this review was initiated to assess the role of baculoviruses in controlling insect pests and indicate research gaps.

2. Methodology

In order to write this review study, we have referred and employed about 96 peer-reviewed papers which are indexed in Web of Science, Scopus, and PubMed. Of which, we principally focused on original research that encompasses an array of data and spaces.

3. Characteristics and classification of entomopathogenic viruses

Viruses are the simplest form of life and consist of a nucleic acid core, DNA or RNA, and a protein shell or capsid, which plays an important role in the host cell infection process (Lucas & Knipe, 2001). This nucleocapsid may also be surrounded by a lipid bilayer envelope and is called a virion (Nour et al., 2013). Some viruses are additionally occluded by a protein matrix, and the matrix is named an occlusion body (OB) (Rohrmann, 1992). OBs are found in some families of viruses and appear to have evolved independently in each family. Insect viruses may be double-stranded (dsDNA) single-stranded DNA (ssDNA) or double-stranded RNA (dsRNA) and single-stranded RNA (ssRNA), enveloped or nonenveloped, and occluded in OB or nonoccluded (Harish et al., 2021). Viruses are considered obligate parasites, as they use not only the cell’s own material but also most of its own metabolic machinery. That is, viruses cannot replicate “in vitro” (i.e., on artificial media, where only organic material sources are provided) (Takayama, 2020). Commercial production of baculoviruses has been produced only in vivo, either by applying the virus to the host insect in the field and by collecting diseased or dead larvae (Moscardi et al., 2011). Each group of viruses shows some intrinsic features, such as morphology, genome infectivity, host range, and chemical resistance, which are distinctive of each group (Payne, 2022).

A variety of viruses attack and kill many insects, and these viruses are called entomopathogenic viruses, which have been found in many insect orders (Raj et al., 2022). Some insect pests are also susceptible to viral infections, and hence, these viruses can be used as biological control agents. Currently, entomopathogenic viruses belonging to the family baculoviridae are the main group of arthropod viral pathogens (Petersen et al., 2022). They have been isolated from 700 species of arthropods and include the most promising viruses for insect biological control (da Silva Sa et al., 2023). Baculoviruses produce characteristic occlusion bodies, ensuring better virus survival in the environment and, most importantly, enabling good insect infestation (Hutchinson, 2021).

Although there is a great diversity of insect viruses, only a few are frequently observed in insect populations, such as baculovirus, cypovirus, entomopoxvirus and iridovirus (Sarwar & Aslam, 2021). Undoubtedly, there are many more insect viruses still to be discovered; however, only a few show the potential to be used as control agents, especially in the case of baculoviruses. The most common and effective type of insect viruses are baculoviruses, which as a group are known to infect over 600 insect species worldwide (Kachhawa, 2017). About 60 baculovirus-based insecticides have been commercially available to control diverse insect pest all over the world (Reid et al., 2023). Some examples of commercial available baculovirus biopesticides registered for insect pest control in different countries are presented in Table 1.

Table 1. List of commercial available baculovirus formulations

product Name	Baculoviruses	Host insect	Reference
Spod-X	NPV	Beet armyworm	(Carson & Trumble, 1997)
GemStar	NPV	Heliothis/Helicoverpa	(Scholz et al., 1998)
Madmex	NPV	Cydia pomenella	(Lacey & Shapiro-Ilan, 2003)
VPN	NPV	Velvetbean caterpillar	(Gomez & Gazzoni, 2000)
Gusano	NPV	Autographa californica	(Inceoglu et al., 2001)
Spodopterin	NPV	Spodoptera litura	(Szewczyk et al., 2009)
Capex 2	GV	Adoxophyes orana	(Vail et al., 1991)
Agrovir	GV	Agrotis segetum	(Cisneros et al., 2002)
Gusano Biological,VPN-80TM VPN-80TM	NPV	Autographa californica	(Thakore, 2006)
Virin-HS	NPV	Helicoverpa armigera	(Beas-Catena et al., 2014)
GemStar, Biotrol	NPV	Helicoverpa zea	(Beas-Catena et al., 2014)
VPN-82, VPN-Ultra	NPV	Spodoptera albula	(Grzywacz & Moore, 2017)
Spod-X, Vir-ex,Spod-X LC, Spod-X LC,	NPV	Spodoptera exigua	(Moscardi et al., 2011)
Spodopterin	NPV	Spodoptera littoralis	(Lacey et al., 2015)
DOA BIO V3	NPV	Spodoptera litura	(Bhutia et al., 2012)

The division of baculoviruses into two major groups, the nucleopolyhedrovirus es (NPV) and granuloviruses (GVs), based on occlusion body morphology defined the major taxonomical divisions of these viruses until the advent of molecular biology (Zhang et al., 2005). Several entomopathogenic viruses have been developed and registered for insect pest control, including NPVs for controlling important caterpillar pests (Heliothis spp.) that attack cotton and other field crops, or those (Spodoptera spp.) that attack vegetable crops, and in some cases forest pests (Orgyia spp.) (Lacey et al., 2015; Singh et al., 2019). Most baculoviruses infect caterpillars, which are the immature form of moths and butterflies (Rodriguez et al., 2012). With respect to GVs, the most successful viruses used as microbial biocontrol agents are the GVs of the codling moth and potato tuber worm, both of which are used in many countries worldwide (Thakore, 2006). NPV infects and kills some of the most important crop pests such as Helicoverpa armigera and Spodoptera litura (Miranti et al., 2023). The GV virus used to manage diamondback moth, Plutella, xylostella, apple codling moth, Cydia pomenella, sugarcane shoot borer, Chilo infuscatellus and coconut rhinoceros beetle, Oryctes rhinoceros (Ramanujam et al., 2014).

The mode of pathogenesis and replication of entomopathogenic viruses varies according to the family, but infection nearly always occurs by ingestion (Abd-Alla et al., 2020). Virions then bind to receptors in the gut and penetrate epithelial cells (Figure 1). In Baculoviruses, the infection often spreads to the haemocoel and then to essential organs and tissues, particularly fat bodies (Alramadhan & Mamay, 2019). Their unique mode of action allows baculoviruses to infect their specific target pests (Szewczyk et al., 2009). They do not produce any toxins or metabolites which could be a concern regarding human health.

Figure 1. The mode action of nucleopolyhedrovirus (NPV) on insect host.

4. The use of entomopathogenic viruses for the management of insect pests

Microbial biopesticides play an important role in providing pest management tools in areas where pesticide resistance, niche markets, and environmental concerns limit the use of chemical pesticide products (Sabbahi et al., 2022). Some viruses are produced as commercial products, most notably for fruit pests, but many others are naturally occurring and can initiate outbreaks without additional inputs (Grzywacz et al., 2014). Entomopathogens contribute to the natural regulation of many populations of arthropods, and much of the research in this area concerns the causal agents of insect diseases and their exploitation for biological pest control (Picciotti et al., 2023). Many entomopathogens can be mass produced, formulated, and applied to pest populations in a manner analogous to chemical pesticides, i.e., as nonpersistent remedial treatments that are released inundatively (Tozlu et al., 2019). Baculovirus biopesticides have many advantages as a tool in integrated pest management (IPM), including high specificity, safe to vertebrates and plants, and ease of genetic manipulation (Beas-Catena et al., 2014).

4.1. Host specificity

Biopesticides generally affect only the target pest and closely related organisms, in contrast to broad-spectrum conventional pesticides that may affect organisms as different as birds, insects, and mammals (Sharma & Malik, 2012). Insect viruses are unable to infect mammals, including humans, which makes them very safe to handle, and most insect viruses are relatively specific, so the risk of non-target effects on beneficial insects is very low (Gupta & Dikshit, 2010). Baculoviruses are known to regulate many insect populations in nature, and their host specificity is very high, usually restricted to a single or a few closely related insect species (Haase et al., 2015). They are among the safest pesticides, with no or negligible effects on non-target organisms, including beneficial insects, vertebrates and plants (Federici, 2003; Haase et al., 2015; Yaqoob et al., 2016). Baculoviruses show a host range limited only to insects and a few other arthropods, which means that the possibility of baculoviruses becoming infective to vertebrates or plants is practically null, which is important for safety purposes during the registration process of a viral product (Del Rincón-Castro & Ibarra, 2011).

4.2. Safe for non target group

The use of entomopathogenic microorganisms (EM) as pest control agents is not only efficient against insect pests but is also ecologically friendly for both humans and non-target creatures (lower pesticide residues) (Deka et al., 2021). Applications of baculovirus show no threat to the environment with residual accumulation and contamination (Mishra et al., 2014). OBs are rapidly degraded in the field, mostly due to UV light inactivation and proteolysis of polyhedra, and no cases of resistance to baculoviruses have been recorded, except for some instances where field-collected individuals were subjected to strong selection under laboratory conditions (Del Rincón-Castro & Ibarra, 2011; Myers & Cory, 2016). Widespread use of synthetic chemical insecticides causes growing concern regarding the risks to human health and negative impacts on the environment. Baculoviruses bring many benefits and allow reduced use of synthetic insecticides when included in integrated pest management (IPM).

4.3. Tools ofintegrated pest management

Entomopathogens can be important tools in IPM strategies in both organic and conventional production systems (Goble et al., 2010). Baculoviruses as microbial insecticides are ideal tools in integrated pest management (IPM) programs as they are usually highly specific to their host insects, thus, they are safe to the environment, humans, other plants, and natural enemies (Deka et al., 2021). Insect viruses are most effective as part of a diverse integrated pest management program, they can provide safe, effective, and sustainable control of a variety of insect pests (Sarwar, 2015). Baculovirus-based pesticides are compatible with integrated pest management strategies, and the expansion of their application will significantly reduce the risks associated with the use of synthetic chemical insecticides (Knox et al., 2015). There are several examples of entomopathogen-based biopesticides that have played a critical role in pest management. In field trials, baculovirus products applied in rotation and tank mixes with chlorantraniliprole, Bacillus thuringiensis products, and spinosad were provided promising control of target pests (Landwehr, 2021). Baculoviruses are feasible to be applied along with other pesticides, as long as they do not degrade the OBs, and that standard spray equipment can be used in the application of these bioinsecticides (Moscardi et al., 2011).

5. Challenges of baculovirus for controlling insect pests

The successful commercialization of insect pathogenic viruses has been limited (Nagrale et al., 2023). Viral insecticide development is hindered by the fact that the viruses are specific to one species or genus, ensuring a relatively small market (Knox et al., 2015). This is mostly due to the higher specificity of a control agent, the narrower its market. From the commercial point of view, this may be a major constraint for investing in such a small market, and this is the main reason why many viral bioinsecticides are developed and produced by nonprofit organizations, such as government agencies. Likewise, viral bioinsecticides are expensive to produce, and this is mostly due to the high costs required to maintain a large insect colony not only because of the needed material but also because this work is very labor-intensive (Del Rincón-Castro & Ibarra, 2011). This is mostly due to NPV strains have only been mass produced in living insects, a costly procedure (Sharma, 2014). Therefore, one of the major drawbacks for the commercialization of viral bioinsecticides is the need to optimize massive production (Kergunteuil et al., 2016).

Another restrictive challenge for the use of baculovirus insecticides in maintaining insect populations below the economic injury threshold is the time taken for a given virus to kill the host insect (Valicente, 2019). Most insect viruses take several days to kill their host insect, during which the pest is still causing damage (Rai & Ingle, 2012). According to the host-virus combination, it can take anywhere from a few days to several weeks for an insect to succumb to baculovirus infection (El-Sheikh & Ashour, 2011). Many baculoviruses may take 4 to 14 days to kill their host, a serious challenge in the use of baculoviruses as biological control agents is their slow infectivity (Grzywacz, 2017). On the other hand, viruses can persist in the environment for months or years, exposed virus particles, such as those on the surface of plants, are quickly inactivated by direct sunlight or high temperatures, which can limit their persistence within a given season (Le Guyader et al., 2000). However, some agricultural practices can reduce persistence between seasons, such as tillage, which buries virus particles in the soil (Linker et al., 2009). The shorter persistence of an application in the field can be considered a limitation, as many producers like long-lasting effects of any control measure (Killeen, 2014). UV irradiation from sunlight is the most important degrading factor of baculoviruses in the field (Šimáčková et al., 2014).

6. Optimizing baculovirus performance using genetic engineering for the control insect

Genetic engineering provides opportunities for enhancing the utilization of viruses for insect control. Research to reduce the killing time of viruses includes the use of genetic engineering to improve the performance of viral insecticides (Thakur et al., 2023). The recent literature on advances made to model viral pathogens of insects shows how the efficacy of wild-type pathogens can be improved (Lacey et al., 2015). Researchers (virologists) have been interested in increasing the effectiveness of viral biocontrol agents through genetic engineering (Hussain et al., 2023; Paul & Das, 2021). Recombinant viruses have been engineered with the goal of improving their pesticidal potential by shortening the time required for infection to kill or incapacitate insect pests and reducing the amount of crop damage as a consequence (Agboola et al., 2022). In addition, by enhancing the speed of action (i.e., reducing the lethal time, LT₅₀) of baculovirus insecticides, genetic engineering has also been used to increase the virulence (i.e., reduce the lethal dose LD₅₀ of the virus) and to modify the host range (Yu et al., 2023).

There are different strategies for successfully optimization of baculovirus insecticides by using genetic engineering (Macauley‐Patrick et al., 2005). Some of the tactics are deletion of a baculovirus gene, thereby reducing the time taken by the baculovirus to kill the host insect; insertion of a gene encoding a toxin, hormone or enzyme such that expression of the transgene by the baculovirus would result in death of the host insect; and insertion of a gut active toxin into the occlusion body of the baculovirus on the basis that toxin action in the gut would synergize baculovirus infectivity (Inceoglu et al., 2006).

6.1. Genetic engineering of baculoviruses for increased virulence

There are several examples of baculoviruses that have been genetically engineered to reduce the amount of virus required for a fatal infection of the targeted insect pest (Snow et al., 2005). Enhancing is a metallopro tease commonly expressed by baculoviruses that degrades insect intestinal mucins in the peritrophic membrane (Guo et al., 2019). Insertion of the enhancing gene derived from Trichoplusia GV enhanced AcMNPV virulence by 2- to 14-fold in various insect species (Merzendorfer, 2013). Conversely, deletion of two enhancing genes from Lymantria dispar MNPV reduced viral strength 12-fold compared to wild-type virus (D’Amico et al., 2013). Deletion of the gene encoding the polyhedral envelope protein that surrounds the OB of AcMNPV resulted in a 6-fold increase in infectivity to first instar trichoplusia compared to that of wild-type virus (Cai et al., 2012). The OBs of this virus that lacked the polyhedral envelope protein dissolved more readily in alkali than the OBs of the wild-type virus. Hence, the reduction in effective dose was attributed to the rapid release and increased availability of ODV in the gut for infection. Curiously, engineering AcMNPV to express an algal virus pyrimidine dimer-specific glycosylase, cvPDG, to reduce the susceptibility of the virus to UV inactivation, significantly increased the virulence of the virus in some species (ANGGRAINI et al., 2022). The dose required to kill S. frugiperda larvae was reduced 16-fold by the expression of cvPDG. A possible explanation for this observation is that cvPDG is toxic to midgut cells, with toxicity facilitating virus entry (ANGGRAINI et al., 2022). Some of the best recombinant baculovirus insecticides developed induce feeding cessation within 24 hours of infection, making them competitive with classical chemical insecticides. The degree of efficacy along with the demonstrated safety of recombinant baculoviruses makes them useful tools for crop protection (Efremenko et al., 2023).

6.2. Genetic modification to reduce the survival time of baculovirus-infected insects

Several baculoviruses have been engineered for improved insecticidal performance to reduce the amount of time taken by the virus to kill the host insect (Reid et al., 2023). These include Rachiplusia nu (Anagrapha falcifera), MNPV (RoMNPV), Helicoverpa zea SNPV (HzSNPV), and Bombyx mori NPV (BmNPV), which have been used as model systems (Chen et al., 2002; Christian et al., 2001; Gomi et al., 1999). Most of the strategies employed to increase the speed of action of baculovirus insecticides have involved the insertion of a transgene into the baculovirus genome (Bai et al., 2023). On replication of the baculovirus within the cells of the infected host, the product of the transgene, usually a toxin or a physiological effector, is expressed along with the baculovirus proteins, and expression of these agents results in paralysis or in disruption of the homeostasis of the host insect (Reid et al., 2023). Hence, baculovirus serves as a delivery system for toxic agents, and death results from expression of the toxin rather than from baculovirus infection (Popham et al., 2016). The agents expressed by recombinant baculovirus insecticides fall into two main categories: neurotoxins (that target the insect nervous system or physiological effectors that disrupt a physiological process such as water balance) or hormonal regulation of development (Schmidt & Bonning, 2009). Of the recombinant baculoviruses developed to date, viruses expressing insect-selective toxins and the protease cathepsin have the greatest potential for insect pest control. Indeed, the insecticidal potential of HzSNPV and AcMNPV expressing the toxin LqhIT2 was assessed for commercial viability for the control of the cotton bollworm Helicoverpa zea Boddie by DuPont Agricultural Products, while AcMNPV expressing the toxin AalT was assessed by American Cyanamid Company (Kamita et al., 2010). These insect-selective toxins are derived from the venom of the scorpions Leiurus quinquestriatus, hebraeus Hemprich & Ehrenberg, and Androctonus australis Hector, respectively. Because of internally changing priorities and competing technologies, both of these corporate programs that were established to develop recombinant baculovirus insecticides for commercialization have been discontinued.

7. Conclusions and future directions

The application of baculoviruses in third-world countries has been constrained by many factors. First, there are no incentives for organic production due to the concern of some governments and the public about the effects of chemical pesticides generated. Second, farmers are not aware of the drawbacks of chemical use (pesticide resistance development and secondary pest resurgence). Third, research advances have not led to a larger inventory of diverse baculovirus species and improvements in biopesticidal production technologies. In addition, the distribution of literature and extension activity does not play a positive role in public perception and farmers’ acceptance of environmentally friendly microbial control agents. Most of the third-world nations are not aware of the efficiency, formulation, application, environmental persistence, and shelf life of baculoviruses.

The use of synthetic insecticides will be continued due to limited information of alternative insect pest management practices, specifically in developing countries like Ethiopia. Thus, effective public extension services, government policies, and farmer education are important to expand the use of viral insecticides as well as for further development in the production and use of these insecticides. In addition, introducing and evaluating commercial available baculoviruses bioinsecticides need to be practiced.

Authors’ contributions

Concept, synthesis, write-up

Availability of data and materials

The dataset that supports the findings of this review is included in the article.

Acknowledgments

The author acknowledges the anonymous editors and potential reviewers for their valuable input on the manuscript.

Disclosure Statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

No funding was received for this manuscript.

Notes on contributors

Yohannes Gelaye

Yohannes Gelaye is a lecturer and researcher in the Department of Horticulture, Debre Markos University, Ethiopia. He did Master’s degree in Horticulture at Bahir Dar University, Ethiopia. He has taught various courses (Vegetable and fruit crops production and management, Ornamental plants production, Plant propagation, Plant physiology, Coffee production, processing and quality control, Design and agricultural experimentation, Protection, Nutrition sensitive agriculture) at Debre Markos University, since December 2014. His research interest is horticulture crops improvement, Postharvest handling and management, Food safety, Soil fertility improvement and management, Nutrition and food security.

Belete Negash

Belete Negash (PhD) is a lecturer and researcher in Debre Markos University, Ethiopia. He did his PhD in agricultural entomology at Hawassa University, Ethiopia. He has been giving different M. Sc courses (IPM, agricultural pesticides, biological control etc.) at Debre Markos University.