Interactions of recombinant and wild-type baculoviruses with classical insecticides and pyrethroid-resistant tobacco budworm (Lepidoptera: Noctuidae)

HearNPV susceptibility in Helicoverpa armigera and Helicoverpa punctigera strains resistant to Bt toxins Cry1Ac, Cry2Ab, and Vip3Aa

Genetically engineered crops expressing insecticidal toxins from Bacillus thuringiensis (Bt) have improved the management of targeted lepidopteran pests and reduced the use of insecticide sprays. These benefits explain an increasing adoption of Bt crops worldwide, intensifying the selection pressure on target species and the risk of resistance. Nucleopolyhedroviruses (NPVs) are effective bioinsecticides against numerous important lepidopteran pests. If Bt-resistant insects are shown to be susceptible to NPVs then these bioinsecticides could be a valuable component of Insecticide Resistance Management (IRM) strategies for Bt crops. We assessed the effectiveness of a Helicoverpa nucleopolyhedrovirus (HearNPV) against several different Bt-resistant strains. Utilising a droplet feeding bioassay we confirmed susceptibility to HearNPV in Helicoverpa punctigera and Helicoverpa armigera larvae resistant to the Bt toxins Cry1Ac, Cry2Ab, and Vip3A. Dual resistant H. punctigera, (Cry1Ac/Cry2Ab, and Cry2Ab/Vip3A) and dual resistant H. armigera (Cry2Ab/Vip3A) were also susceptible to HearNPV. Regardless of their specific resistance profile, Bt-resistant larvae displayed statistically similar lethal concentration (LC₅₀) and lethal time (LT₅₀) responses to HearNPV when compared to Bt-sensitive control insects. These results indicate that Bt-resistant H. armigera and H. punctigera are not cross-resistant to HearNPV. Consequently, the use of HearNPV against these pests may be a valuable tool to an IRM strategy for controlling Bt-resistant populations.

Synergy of Lepidopteran Nucleopolyhedroviruses AcMNPV and SpliNPV with Insecticides

The joint use of baculoviruses and synthetic insecticides for integrated pest management requires the study of the additive, synergistic or antagonistic effects among them on pest mortality. Droplet bioassays were conducted with Autographa californica multiple nucleopolyhedrovirus (AcMNPV), Spodoptera littoralis nucleopolyhedrovirus (SpliNPV) and seven insecticides (azadirachtin, Bacillus thuringiensis, cyantraniliprole, emamectin, metaflumizone, methoxyfenozide and spinetoram) on Spodoptera exigua and Spodoptera littoralis. The lethal concentrations LC₅₀ and LC₉₅ were calculated through probit regressions. Then, the sequential feeding of insecticides and nucleopolyhedroviruses was studied. Larvae were provided with the LC₅₀ of one insecticide, followed by the LC₅₀ of one nucleopolyhedrovirus 24 h later. The inverse order was also conducted. The insecticide LC₅₀ and LC₉₅ were higher for S. littoralis than for S. exigua. AcMNPV showed greater toxicity on S. exigua than SpliNPV on S. littoralis. Emamectin showed synergy with AcMNPV when the chemical was applied first, and metaflumizone and AcMNPV were synergistic regardless of the order of application, both from the first day of evaluation. SpliNPV was synergistic with azadirachtin and emamectin when it was applied first, but synergy was reached after 12–13 days. Excellent control is possible with the LC₅₀ of azadirachtin, emamectin and metaflumizone in combination with nucleopolyhedroviruses, and merits further study as a means of controlling lepidopteran pests.

Tying pest insects in knots: the deployment of spider-venom-derived knottins as bioinsecticides

Spider venoms are complex chemical arsenals that contain a rich variety of insecticidal toxins. However, the major toxin class in many spider venoms is disulfide-rich peptides known as knottins. The knotted three-dimensional fold of these mini-proteins provides them with exceptional chemical and thermal stability as well as resistance to proteases. In contrast with other bioinsecticides, which are often slow-acting, spider knottins are fast-acting neurotoxins. In addition to being potently insecticidal, some knottins have exceptional taxonomic selectivity, being lethal to key agricultural pests but innocuous to vertebrates and beneficial insects such as bees. The intrinsic oral activity of these peptides, combined with the ability of aerosolized knottins to penetrate insect spiracles, has enabled them to be developed commercially as eco-friendly bioinsecticides. Moreover, it has been demonstrated that spider-knottin transgenes can be used to engineer faster-acting entomopathogens and insect-resistant crops. © 2019 Society of Chemical Industry.

Application of the Scorpion Neurotoxin AaIT against Insect Pests

Androctonus australis Hector insect toxin (AaIT), an insect-selective toxin, was identified in the venom of the scorpion Androctonus australis. The exclusive and specific target of the toxin is the voltage-gated sodium channels of the insect, resulting in fast excitatory paralysis and even death. Because of its strict toxic selectivity and high bioactivity, AaIT has been widely used in experiments exploring pest bio-control. Recombinant expression of AaIT in a baculovirus or a fungus can increase their virulence to insect pests and diseases vectors. Likewise, transgenic plants expressing AaIT have notable anti-insect activity. AaIT is an efficient toxin and has great potential to be used in the development of commercial insecticides.

Lethal effects of an insecticidal spider venom peptide involve positive allosteric modulation of insect nicotinic acetylcholine receptors

κ-Hexatoxins (κ-HXTXs) are a family of excitotoxic insect-selective neurotoxins from Australian funnel-web spiders that are lethal to a wide range of insects, but display no toxicity towards vertebrates. The prototypic κ-HXTX-Hv1c selectively blocks native and expressed cockroach large-conductance calcium-activated potassium (BK_Ca or K_Ca1.1) channels, but not their mammalian orthologs. Despite this potent and selective action on insect K_Ca1.1 channels, we found that the classical K_Ca1.1 blockers paxilline, charybdotoxin and iberiotoxin, which all block insect K_Ca1.1 channels, are not lethal in crickets. We therefore used whole-cell patch-clamp analysis of cockroach dorsal unpaired median (DUM) neurons to study the effects of κ-HXTX-Hv1c on sodium-activated (K_Na), delayed-rectifier (K_DR) and 'A-type' transient (K_A) K⁺ channels. 1 μM κ-HXTX-Hv1c failed to significantly inhibit cockroach K_Na and K_DR channels, but did cause a 30 ± 7% saturating inhibition of K_A channel currents, possibly via a Kv4 (Shal-like) action. However, this modest action at such a high concentration of κ-HXTX-Hv1c would indicate a different lethal target. Accordingly, we assessed the actions of κ-HXTX-Hv1c on neurotransmitter-gated ion channels in cockroach DUM neurons. We found that κ-HXTX-Hv1c failed to produce any major effects on GABA_A or glutamate-Cl receptors but dramatically slowed nicotine-evoked ACh receptor (nAChR) current decay and reversed nAChR desensitization. These actions occurred without any alterations to nAChR current amplitude or the nicotine concentration-response curve, and are consistent with a positive allosteric modulation of nAChRs. κ-HXTX-Hv1c therefore represents the first venom peptide that selectively modulates insect nAChRs with a mode of action similar to the excitotoxic insecticide spinosyn A. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'

Molecular basis of the remarkable species selectivity of an insecticidal sodium channel toxin from the African spider Augacephalus ezendami

The inexorable decline in the armament of registered chemical insecticides has stimulated research into environmentally-friendly alternatives. Insecticidal spider-venom peptides are promising candidates for bioinsecticide development but it is challenging to find peptides that are specific for targeted pests. In the present study, we isolated an insecticidal peptide (Ae1a) from venom of the African spider Augacephalus ezendami (family Theraphosidae). Injection of Ae1a into sheep blowflies (Lucilia cuprina) induced rapid but reversible paralysis. In striking contrast, Ae1a was lethal to closely related fruit flies (Drosophila melanogaster) but induced no adverse effects in the recalcitrant lepidopteran pest Helicoverpa armigera. Electrophysiological experiments revealed that Ae1a potently inhibits the voltage-gated sodium channel BgNa_V1 from the German cockroach Blattella germanica by shifting the threshold for channel activation to more depolarized potentials. In contrast, Ae1a failed to significantly affect sodium currents in dorsal unpaired median neurons from the American cockroach Periplaneta americana. We show that Ae1a interacts with the domain II voltage sensor and that sensitivity to the toxin is conferred by natural sequence variations in the S1–S2 loop of domain II. The phyletic specificity of Ae1a provides crucial information for development of sodium channel insecticides that target key insect pests without harming beneficial species.

Evaluation of the Insecticidal Efficacy of Wild Type and Recombinant Baculoviruses

A considerable amount of work has been undertaken to genetically enhance the efficacy of baculovirus insecticides. Following construction of a genetically altered baculovirus, laboratory bioassays are used to quantify various parameters of insecticidal activity such as the median lethal concentration (or dose) required to kill 50 % of infected larvae (LC50 or LD50), median survival of larvae infected (ST50), and feeding damage incurred by infected larvae. In this chapter, protocols are described for a variety of bioassays and the corresponding data analyses for assessment of the insecticidal activity of baculovirus insecticides.

A novel method using Autographa californica multiple nucleopolyhedrovirus for increasing the sensitivity of insecticide through calcium influx in insect cell line

Due to an intensive use of chemical insecticides, resistance mechanisms to insecticides together with adverse effects on non-target organisms have been largely reported. Improvement in pest control strategy represents an urgent need to optimize efficiency in the control of pest insects. In this context, a novel method based on the use of insect specific virus applied in combination with chemical insecticide, which could lead to sensitization of the insect target to insecticides is described. Insect virus, the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV), applied onto Sf9 cells induces an increase of intracellular calcium concentration via extracellular calcium influx. Co-application of AcMNPV with chlorpyrifos-ethyl onto Sf9 cells expressing the key enzyme acetylcholinesterase (AChE), known to be targeted by organophosphate insecticides, increases 1.5-fold the sensitivity of AChE to the insecticide. This effect is correlated with intracellular calcium concentration rise since AcMNPV-induced potentiating insecticide effect is counteracted by pretreatment with the calcium channel blocker, cadmium chloride. Increasing insecticide target sensitivity through intracellular calcium modulation by using insect virus co-applied with a chemical insecticide is a very promising strategy allowing optimization of insecticide treatment while reducing the concentration of insecticides used.

Spider-venom peptides: structure, pharmacology, and potential for control of insect pests

Spider venoms are an incredibly rich source of disulfide-rich insecticidal peptides that have been tuned over millions of years to target a wide range of receptors and ion channels in the insect nervous system. These peptides can act individually, or as part of larger toxin cabals, to rapidly immobilize envenomated prey owing to their debilitating effects on nervous system function. Most of these peptides contain a unique arrangement of disulfide bonds that provides them with extreme resistance to proteases. As a result, these peptides are highly stable in the insect gut and hemolymph and many of them are orally active. Thus, spider-venom peptides can be used as stand-alone bioinsecticides, or transgenes encoding these peptides can be used to engineer insect-resistant crops or enhanced entomopathogens. We critically review the potential of spider-venom peptides to control insect pests and highlight their advantages and disadvantages compared with conventional chemical insecticides.

Spider-venom peptides as bioinsecticides

Over 10,000 arthropod species are currently considered to be pest organisms. They are estimated to contribute to the destruction of ~14% of the world's annual crop production and transmit many pathogens. Presently, arthropod pests of agricultural and health significance are controlled predominantly through the use of chemical insecticides. Unfortunately, the widespread use of these agrochemicals has resulted in genetic selection pressure that has led to the development of insecticide-resistant arthropods, as well as concerns over human health and the environment. Bioinsecticides represent a new generation of insecticides that utilise organisms or their derivatives (e.g., transgenic plants, recombinant baculoviruses, toxin-fusion proteins and peptidomimetics) and show promise as environmentally-friendly alternatives to conventional agrochemicals. Spider-venom peptides are now being investigated as potential sources of bioinsecticides. With an estimated 100,000 species, spiders are one of the most successful arthropod predators. Their venom has proven to be a rich source of hyperstable insecticidal mini-proteins that cause insect paralysis or lethality through the modulation of ion channels, receptors and enzymes. Many newly characterized insecticidal spider toxins target novel sites in insects. Here we review the structure and pharmacology of these toxins and discuss the potential of this vast peptide library for the discovery of novel bioinsecticides.

Evaluation of the insecticidal efficacy of wild-type and recombinant baculoviruses

A considerable amount of work has been done during the last 20 yr to genetically enhance the efficacy of baculovirus insecticides. Following construction of a genetically altered baculovirus, laboratory bioassays are used to quantify various parameters of insecticidal activity such as the median lethal concentration (or dose) required to kill 50% of infected larvae (LC50 or LD50), median survival time of larvae infected at a fixed dose (ST50), and feeding damage incurred by infected larvae. In this chapter, protocols are described for a variety of bioassays and corresponding data analyses for assessment of the insecticidal activity or host range of baculovirus insecticides. Methods are also provided for baculovirus inoculation of larvae using a microapplicator for determining ST50 or for examining physiological effects.

The insecticidal potential of scorpion β-toxins

Voltage-gated sodium channels are a major target for toxins and insecticides due to their central role in excitability, but due to the conservation of these channels in Animalia most insecticides do not distinguish between those of insects and mammals, thereby imposing risks to humans and livestock. Evidently, as long as modern agriculture depends heavily on the use of insecticides there is a great need for new substances capable of differentiating between sodium channel subtypes. Such substances exist in venomous animals, but ways for their exploitation have not yet been developed due to problems associated with manufacturing, degradation, and delivery to the target channels. Engineering of plants for expression of anti-insect toxins or use of natural vectors that express toxins near their target site (e.g. baculoviruses) are still problematic and raise public concern. In this problematic reality a rational approach might be to learn from nature how to design highly selective anti-insect compounds preferably in the form of peptidomimetics. This is a complex task that requires the elucidation of the face of interaction between insect-selective toxins and their sodium channel receptor sites. This review delineates current progress in: (i) elucidation of the bioactive surfaces of scorpion beta-toxins, especially the excitatory and depressant groups, which show high preference for insects and bind insect sodium channels with high affinity; (ii) studies of the mode of interaction of scorpion beta-toxins with receptor site-4 on voltage-gated sodium channels; and (iii) clarification of channel elements that constitute receptor site-4. This information may be useful in future attempts to mimic the bioactive surface of the toxins for the design of anti-insect selective peptidomimetics.

Insect-selective spider toxins targeting voltage-gated sodium channels

The voltage-gated sodium (Na(v)) channel is a target for a number of drugs, insecticides and neurotoxins. These bind to at least seven identified neurotoxin binding sites and either block conductance or modulate Na(v) channel gating. A number of peptide neurotoxins from the venoms of araneomorph and mygalomorph spiders have been isolated and characterized and determined to interact with several of these sites. These all conform to an 'inhibitor cystine-knot' motif with structural, but not sequence homology, to a variety of other spider and marine snail toxins. Of these, spider toxins several show phyla-specificity and are being considered as lead compounds for the development of biopesticides. Hainantoxin-I appears to target site-1 to block Na(v) channel conductance. Magi 2 and Tx4(6-1) slow Na(v) channel inactivation via an interaction with site-3. The delta-palutoxins, and most likely mu-agatoxins and curtatoxins, target site-4. However, their action is complex with the mu-agatoxins causing a hyperpolarizing shift in the voltage-dependence of activation, an action analogous to scorpion beta-toxins, but with both delta-palutoxins and mu-agatoxins slowing Na(v) channel inactivation, a site-3-like action. In addition, several other spider neurotoxins, such as delta-atracotoxins, are known to target both insect and vertebrate Na(v) channels most likely as a result of the conserved structures within domains of voltage-gated ion channels across phyla. These toxins may provide tools to establish the molecular determinants of invertebrate selectivity. These studies are being greatly assisted by the determination of the pharmacophore of these toxins, but without precise identification of their binding site and mode of action their potential in the above areas remains underdeveloped.

Genetically modified baculoviruses: a historical overview and future outlook

The concept of using genetic engineering to improve the natural insecticidal activity of baculoviruses emerged during the 1980s. Both academic and industrial laboratories have since invested a great deal of effort to generate genetically modified (GM) or recombinant baculoviruses with dramatically improved speeds of kill. Optimal production methodologies and formulations have also been developed, and the safety and ecology of the recombinant baculoviruses have been thoroughly investigated. Unfortunately, the initial excitement that was generated by these technologies was tempered when industry made a critical decision to not complete the registration process of GM baculoviruses for pest insect control. In this chapter, we summarize the developments in the field from a historical perspective and provide our opinions as to the current status and future potential of the technology. We will argue that GM baculoviruses are valuable and viable tools for pest insect control both alone and in combination with wild-type viruses. We believe that these highly effective biopesticides still have a bright future in modern agriculture as public awareness and acceptance of GM organisms, including GM baculoviruses, increases.

Baculoviruses-- re-emerging biopesticides

Biological control of agricultural pests has gained importance in recent years due to increased pressure to reduce the use of agrochemicals and their residues in the environment and food. Viruses of a few families are known to infect insects but only those belonging to the highly specialized family Baculoviridae have been used as biopesticides. They are safe to people and wildlife, their specificity is very narrow. Their application as bioinsecticides was limited until recently because of their slow killing action and technical difficulties for in vitro commercial production. Two approaches for the wider application of baculoviruses as biopesticides will be implemented in future. In countries where use of genetically modified organisms is restricted, the improvements will be mainly at the level of diagnostics, in vitro production and changes in biopesticide formulations. In the second approach, the killing activity of baculoviruses may be augmented by genetic modifications of the baculovirus genome with genes of another natural pathogen. It is expected that the baculoviruses improved by genetic modifications will be gradually introduced in countries which have fewer concerns towards genetically modified organisms.

Allosteric interactions among pyrethroid, brevetoxin, and scorpion toxin receptors on insect sodium channels raise an alternative approach for insect control

Intensive pyrethroid use in insect control has led to resistance buildup among various pests. One alternative to battle this problem envisions the combined use of synergistically acting insecticidal compounds. Pyrethroids, scorpion alpha- and beta-toxins, and brevetoxins bind to distinct receptor sites on voltage-gated sodium channels (NaChs) and modify their function. The binding affinity of scorpion alpha-toxins to locust, but not rat-brain NaChs, is allosterically increased by pyrethroids and by brevetoxin-1. Brevetoxin-1 also increases the binding of an excitatory beta-toxin to insect NaChs. These results reveal differences between insect and mammalian NaChs and may be exploited in new strategies of insect control.

Recombinant baculoviruses for insect control

Baculoviruses are double-stranded DNA viruses which are highly selective for several insect groups. They are valuable natural control agents, but their utility in many agricultural applications has been limited by their slow speed of kill and narrow host specificity. Baculoviruses have been genetically modified to express foreign genes under powerful promoters in order to accelerate their speed of kill. In our and other laboratories, the expression of genes coding for insect juvenile hormone esterases and various peptide neurotoxins has resulted in recombinant baculoviruses with promise as biological insecticides. These viruses are efficacious in the laboratory, greenhouse and field and dramatically reduce damage caused by insect feeding. The recombinant viruses synergize and are synergized by classical pesticides such as pyrethroids. Since they are highly selective for pest insects, they can be used without disrupting biological control. Because the recombinant virus produces fewer progeny in infected larvae than the wild-type virus, they are rapidly out-competed in the ecosystem. The viruses can be used effectively with crops expressing endotoxins of Bacillus thuringiensis. They can be produced industrially but also by village industries, indicating that they have the potential to deliver sustainable pest control in developing countries. It remains to be seen, however, whether the current generation of recombinant baculoviruses will be competitive with the new generation of synthetic chemical pesticides. Current research clearly indicates, though, that the use of biological vectors of genes for insect control will find a place in agriculture. Baculoviruses will also prove valuable in testing the potential utility of proteins and peptides for insect control.

AaIT: from neurotoxin to insecticide

AaIT is a single chain neurotoxic polypeptide derived from the venom of the Buthid scorpion Androctonus australis Hector, composed of 70 amino acids cross-linked by four disulfide bridges. Its strict selectivity for insects has been documented by toxicity, electrophysiological and ligand receptor binding assays. These last have shown that various insect neuronal membranes possess a single class of non-interacting AaIT binding sites of high affinity (K(D) = 1-3(n)M) and low capacity (0.5-2.0 pmol/mg prot.). The fast excitatory paralysis induced by AaIT is a result of a presynaptic effect, namely the induction of a repetitive firing in the terminal branches of the insect's motor nerves resulting in a massive and uncoordinated stimulation of the respective skeletal muscles. The neuronal repetitive activity is attributed to an exclusive and specific perturbation of sodium conductance as a consequence of toxin binding to external loops of the insect voltage-dependent sodium channel and modification of its gating mechanism. From a strictly agrotechnical point of view AaIT involvement in plant protection has taken the following two complementary forms: firstly, as a factor for the genetic engineering of insect infective baculoviruses resulting in potent and selective bio-insecticides. The efficacy of the AaIT-expressing, recombinant baculovirus is attributed mainly to its ability to continuously provide and translocate the gene of the expressed toxin to the insect central nervous system; secondly, based on the pharmacological flexibility of the voltage-gated sodium channel, as a device for insecticide resistance management. Channel mutations conferring resistance to a given class of insecticidal agents (such as the KDR phenomenon) may greatly increase susceptibility to the AaIT expressing bioinsecticides. Thus the AaIT is a pharmacological tool for the study of insect neuronal excitability and chemical ecology and the development of new approaches to insect control.

Deterministic modeling of negative cross-resistance strategies for use in transgenic host-plant resistance

Negative cross-resistance refers to a situation in which an insect population that is tolerant (resistant, virulent) to one insecticide is hyper-sensitive (avirulent) to a second insecticide and insects hyper-sensitive to the first compound are tolerant to the second. Most research dealing with negative cross-resistance has focused on the molecular biology and chemical aspects of this phenomenon. We explored, from a population genetics perspective, whether negative cross-resistance is feasible in the control of an insect population. As a first step towards this goal, we used a deterministic approach to evaluate different control scenarios and to identify some of the potential limitations of negative cross-resistance strategies. Specifically, we investigated how such approaches could be used in a host-plant resistance program. Homo- and heterozygous insect fitness influenced the effectiveness of the toxins in controlling the insect population. The negative cross-resistance strategy was most useful when the insects' virulence to both host-plant toxins was recessive. When virulence was dominant, there were many periods when intervention with an outside (or third) class of compounds, which had a different mode of action than that of the negative cross-resistance compounds, was needed to control the insect population. The greater the number of insect generations per plant generation, in the absence of immigration or emigration in the insect population, the greater the requirement for intervention with a third class of compound to maintain effective control of the insect population. When the toxins were rotated every insect generation, and virulence in the insect was recessive to both toxins, effective control of the insect population was maintained without intervention of a third class of compounds.

The insect voltage-gated sodium channel as target of insecticides

Examination of the function, chemistry, and pharmacology of the voltage-gated insect sodium channel (ISC) reveals that the ISC closely resembles its vertebrate counterpart in electrophysiology and ion conductance, primary structure and allocation of all functional domains, and its pharmacological diversity and flexibility exhibited by the occurrence of different allosterically coupled receptor-binding sites for various neurotoxicants. The toxicants include several groups of insecticides, namely DDT and its analogues, pyrethroids, N-alkylamides, and dihydropyrazoles, which affect channel gating and ion permeability. Despite their similarity, the insect and vertebrate channels are pharmacologically distinguishable, as revealed by the responsiveness of the heterologously expressed Drosophila para clone to channel modifiers and blockers and the occurrence of the insect-selective sodium channel neurotoxins derived from arachnid venoms presently used for the design of recombinant baculovirus-mediated selective bioinsecticides. The pharmacological specificity of the ISC may lead to the design of insect-selective toxicants, and its pharmacological flexibility may direct the use of ISC insecticides for resistance management. Insecticide resistance [such as knockdown resistance (KDR)] is acquired by natural selection and operated by increased metabolism, channel mutagenesis, or both. The resistance issue can be dealt with in several ways. One is by simultaneous application of low doses of synergistic, allosterically coupled mixtures (thus delaying or preventing the onset of resistance). An alternative is to replace an insecticide to which resistance was acquired by channel mutation with a different ISC toxicant to which increased susceptibility was conferred by the same mutation. Such a possibility was exemplified by a significant increase in susceptibility to N-alkylamides, as well as an insect-selective neurotoxin revealed by KDR insects. Third, both of these methods can be combined. Thus owing to its pharmacological uniqueness, the ISC may serve as a high-priority target for future selective and resistance-manageable insecticides.

Assessment of the application of baculoviruses for control of Lepidoptera

Baculoviruses, among other insect viruses, are regarded as safe and selective bioinsecticides, restricted to invertebrates. They have been used worldwide against many insect pests, mainly Lepidoptera. Their application as microbial pesticides, however, has not met their potential to control pests in crops, forests, and pastures, with the exception of the nuclear polyhedrosis virus of the soybean caterpillar (Anticarsia gemmatalis), which is used on approximately 1 million ha annually in Brazil. Problems that have limited expansion of baculovirus use include narrow host range, slow killing speed, technical and economical difficulties for in vitro commercial production, timing of application based on frequent host population monitoring, variability of field efficacy due to climatic conditions, and farmers' attitudes toward pest control, which have been based on application of fast-killing chemical insecticides. Farmer education regarding use of biological insecticides and their characteristics is considered one of the major actions necessary for increased use of baculoviruses. Strategies to counteract some of the limitations of baculoviruses, especially their slow killing activity, have been investigated and are promising. These include the use of chemical or biological substances added to virus formulations and genetic engineering of the viruses themselves to express insect toxins or hormones. Such strategies can enhance viral activity and increase speed of kill as well as reduce larval feeding activity. The use of baculoviruses against Lepidoptera is reviewed, with the utilization of the nuclear polyhedrosis virus of A. gemmatalis in Brazil serving as a case-study.