Natural and Engineered Pest Management Agents - American

Chapter 27

Formulation and Application of Viral Insecticides S. Y. Young Downloaded by UNIV OF ALBERTA on November 26, 2014 | http://pubs.acs.org Publication Date: December 20, 1993 | doi: 10.1021/bk-1994-0551.ch027

Department of Entomology, University of Arkansas, Fayetteville, AR 72701

Methodologies most often used for formulation and a p p l i cation of v i r a l insecticides are those developed for conventional chemical insecticides. V i r a l insecticides are most e f f e c t i v e l y formulated as wettable powders by l y o p h i l i z a t i o n or spray dry methods. These formulations are best standardized using both counts of occluded virus p a r t i c l e concentration and bioassay a c t i v i t y . Viral insecticides are t y p i c a l l y applied as sprays against l a r v a l pests of Lepidoptera and Hymenoptera (sawfly) using both a e r i a l and ground equipment. Spray parameters for v i r a l insecticides are not well understood and a v a i l able equipment is not suitable for their most efficaceous use. Much of the research on virus application has been on development of adjuvants for tank mixtures to overcome problems with plant coverage and sunlight i n a c t i v a t i o n . V i r a l diseases have been isolated from several hundred insect species (1). Although these viruses represent several families, those studied for use as control agents are almost exclusively limited to occluded viruses (nuclear polyhedrosis [NPV] and granul o s i s [GV]) of Baculoviridae. Known occluded baculoviruses are mostly r e s t r i c t e d to larvae of Lepidoptera and Hymenoptera (sawf l i e s ) , thus l i m i t i n g v i r a l insecticide development primarily to these two orders. These viruses are safe (2, 3), v i r u l e n t , e f f i caceous (4) and can be produced i n quantity i n insect hosts. Virus efficacy is t y p i c a l l y assessed i n terms r e l a t i v e to the efficacy of standard chemical insecticides, and they seldom fare well i n this comparison. Although numerous viruses have been tested i n the f i e l d as insecticides, few have been developed as viable commercial products. Pesticide formulation and application technology has p a r a l l e l e d the development of synthetic pesticides, accordingly virus formulation and application methodology was copied from t h i s .

0097-6156/94/0551-0384$06.00/0 © 1994 American Chemical Society In Natural and Engineered Pest Management Agents; Hedin, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.

Downloaded by UNIV OF ALBERTA on November 26, 2014 | http://pubs.acs.org Publication Date: December 20, 1993 | doi: 10.1021/bk-1994-0551.ch027

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The formulation and application of v i r a l products using methodology for chemical insecticides may be expedient. However, the a p p l i c a b i l i t y of formulation c r i t e r i a and application technology developed for the fast acting, contact poisons of low molecular weight may be limited for the r e l a t i v e l y unstable, slow-acting v i r a l pathogens that must be consumed to be infectious and effective. Application of v i r a l products is i n effect an inundative release of a b i o l o g i c a l control agent. They can be very e f f i c a cious when applied i n IPM systems where their benign effects on b e n e f i c i a l insects (5) and disease producing potential are desirable and advantageous (6, 7). The numerous research programs around the world on development of v i r a l insecticides have resulted i n a wide array of techn i c a l reports on their formulation and application. There is l i t t l e current research i n this area, and available information has been reviewed i n depth i n numerous reviews (4, 8-14). This report w i l l summarize progress i n these areas and elaborate on areas where the need for additional progress is most c r i t i c a l . FORMULATION Formulation requirements for v i r a l insecticides to those of conventional chemical insecticides (10). t i o n must be a standardized product with l i t t l e loss during the formulation process, i t must be stable i n have good mixing and spraying q u a l i t i e s i n the f i e l d . tives must be safe to animals (2, 3) and plants.

are similar The formulaof a c t i v i t y storage, and The addi-

Methods of Formulation Formulation as Sprays. Virus formulations have usually been for application as sprays using conventional application equipment. Most viruses tested by researchers i n f i e l d t r i a l s have been aqueous suspensions of f i l t r a t e s or precipitates from macerated v i r u s - k i l l e d cadavers. These are stable for long periods under r e f r i g e r a t i o n or when frozen and usually are easily tank-mixed with water and other adjuvants (12, 13). Performance of these simple formulations i n f i e l d t r i a l s usually is equal or superior to more elaborate formulations. They are seldom p r a c t i c a l for commercialization, however. Commercial formulations are concentrated precipitates because stable and concentrated product is needed for storage and shipping. Attempts to improve virus formulations have been primarily by the product registrant, especially private industry as this is where much of the formulation expertise exists. Commercial formulations have often been wettable powder, because the particulate nature of virus makes formulation of flowables d i f f i c u l t . Virus in dry formulations t y p i c a l l y exhibits better shelf l i f e than i n l i q u i d formulations (12). It must be noted, however, that not a l l dry formulations are stable, p a r t i c u l a r l y those formulated as acetone p r e c i p i t a t e s . When formulated as an acetone extract, the early experimental formulations of Helicoverpa zea NPV, including Viron-H (International Minerals and Chemical Corp., L i b e r t y v i l l e , IL) l o s t a c t i v i t y between shipment i n the spring to the s c i e n t i s t s

In Natural and Engineered Pest Management Agents; Hedin, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.

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studying their efficacy against cotton insects and the end of the cotton producing season i n the summer (10). Although acetone precipitates mix well for use as sprays, this procedure is seldom desirable. Lyophilization is often used effectively i n formulation of viruses, but i t may be expensive. A common problem with l y o p h i l ized products is clumping of virus in the l y o p h i l i z a t i o n step. Although m i l l i n g can powder the lyophilate, some clumping of polyhedra remains, l i m i t i n g dispersal i n the tank mixture (15). The U. S. Forest Service uses l y o p h i l i z a t i o n followed by m i l l i n g to formulate both Lymantria dispar NPV (Gypchek) and Orgy La pseudotsugata NPV (TM-Biocontrol-1). Formulation as Dusts or Granules. Viruses formulated as dusts or granules, but these effective than sprays. The H. zea NPV has dust using attaclay (16) and with cellulose wheat or corn (27). Plodia interpunctella as a dust using wheat flour (28).

have been occasionally have usually been less been formulated as a plus cottonseed meal, GV has been formulated

Formulation using Microencapsulation Techniques. Viruses have been formulated as wettable powders using microencapsulation techniques. The H. zea NPV was formulated on two occasions by microencapsulation using c e l l u l o s e , gelatin or polymer formed from styrene maleic anhydride (29, 20). The greatest advance i n formul a t i o n was made by Sandoz, Inc. (Palo A l t o , CA) using spray-dry techniques. In this process a microencapsulated wettable powder is produced by spray-drying the virus with clay and other d i l u ents . This procedure was used to produce several experimental formulations of H. zea NPV which were more stable, exhibited greater a c t i v i t y per unit of product and resulted i n desirable spray q u a l i t i e s (20, 21). Sandoz 240-070-2WP, one of the most effective of these, was registered as Elcar and b r i e f l y marketed for suppression of heliothine species i n cotton. Sandoz Agro, Inc. has since used this process to successfully formulate several other experimental v i r a l products including Syngrapha falcifera NPV and Autographa californica NPV (Sandoz 404). This procedure is apparently not applicable to a l l N P V s , however, as the Choristonura NPV l o s t much a c t i v i t y when formulated by this process (10). A l so, the spray dry formulation of Laspeyresia pomonella GV (Sandoz 406) was not stable as the loss of active product during storage was excessive. S t a b i l i t y i n Storage. S t a b i l i t y i n storage is p a r t i c u l a r l y important for v i r a l insecticides. Most chemical insecticides have an array of potential usages and can be stored for lengthy periods at room temperature without loss of a c t i v i t y . The baculovirus host ranges are often limited to closely related species within an order and their efficaceous use is confined to one or a few pest species i n appropriate IPM systems. Therefore, long periods may be required between opportunities for use. At present, i t is recommended that virus products be stored refrigerated or frozen. These storage conditions are not readily available, thus putting


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virus products at a competitive disadvantage with chemical insecticides .


Standardization Standardization of virus formulations is more d i f f i c u l t than for chemical insecticides. Although viruses have been standardized on a weight basis i n dry formulations, this is unsatisfactory (22) as viruses may lose a c t i v i t y i n storage. In addition, the quantity of virus produced i n cadavers may be influenced by a variety of factors and comparable procedures of preparation may result i n considerable differences i n virus y i e l d per unit weight. Viruses have also been standardized by counts of occluded virus under a l i g h t microscope. However, this method may provide e r r a t i c results as a c t i v i t y per polyhedra can d i f f e r and can be reduced during storage without discernable breakdown under the microscope. Standardization of virus a c t i v i t y by bioassay against larvae of a susceptible host is a more successful method of standardizing virus formulations. However, they are time consuming, expensive and data are often less precise than desired (22, 23). The most commonly used bioassay is diet surface treatment (24). A recently developed bioassay is a virus suspension feeding method (25). For some situations this method may be preferred to the diet method, but although larvae older than neonates need to be starved p r i o r to exposure for consistent r e s u l t s . The most successful standardi z a t i o n protocols have employed both polyhedral counts and bioassay. Spray Adjuvants V i r a l formulations may contain ingredients to increase i n s e c t i c i dal a c t i v i t y of the applied product such as surface active agents, u l t r a v i o l e t l i g h t screens or gustatory stimulants. These materials may present problems when included i n the primary formulation, and are often not added u n t i l the product is mixed i n the spray tank (tank mixtures). Adjuvants added to the primary formulation often s i g n i f i c a n t l y dilute the product and may increase the expense of shipping and storage. Furthermore, adjuvants may not be compatible with the virus formulation, reducing a c t i v i t y during formulation and (or) decreasing s t a b i l i t y during storage. Acetone precipitates of virus have been produced with sugar (26) to obtain a product that is easily resuspended for spraying. Lyophilization of virus i n sugar can also reduce the clumping of polyhedra encountered i n this process. Several experimental formulations have been developed that retard sunlight i n a c t i v a t i o n and extend f i e l d persistence. Microencapsulated H. zea NPV products of National Cash Register Company (Dayton, OH) and Southwest Research Institute (San Santonio, TX) contained UV screens that provided a high l e v e l of persistence for several days i n the f i e l d (19, 27). Both formulation encapsulation procedures result i n unacceptable losses i n virus a c t i v i t y during the process, however. Recently sunlight protectants were included i n formulations produced by starch encapsulation technology. The addition of activated carbon, dye, stelbene fluorescent brightners (28) or



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polyflavanoid s i g n i f i c a n t l y increase persistence of the virus i n formulations exposed to UV l i g h t . Although the process is simple, inexpensive and increases virus persistence, the p a r t i c l e size produced i s considered too large for formulation of viruses (29). Sandoz, Inc. also developed spray-dry products of H. zea NPV, Sandoz-240-070-3 and Sandoz-240-070-5, that contain UV screen which extends virus a c t i v i t y i n cotton f i e l d s (21). Formulation of v i r a l products has been more d i f f i c u l t than that of chemical i n s e c t i c i d e s . No single method has been successf u l for a l l viruses. Although aqueous preparations of f i l t r a t e s of v i r u s - k i l l e d cadavers are feasible for small quantities of product and inexpensive, they are not desirable for formulations of large quantities of virus due to the d i l u t e nature of the preparations and i n s t a b i l i t y from a c t i v i t y loss and b a c t e r i a l contamination during long term storage at room temperature. The more successful formulations have been wettable powders from spray-dry methods, provided a c t i v i t y is not lost during the formul a t i o n or l y o p h i l i z a t i o n processes or storage. Chemicals to improve performance of the virus i n the f i e l d should seldom be included i n the primary formulation i f they can be e f f e c t i v e l y added to the tank mixture at application. APPLICATION V i r a l insecticides are t y p i c a l l y used i n situations where they must compete with chemical insecticides for a market share. Further, they are applied with equipment that was developed for dispensing chemical i n s e c t i c i d e s . Although they are seldom as efficaceous ( i . e . less mortality and slower-acting) as most chemical i n s e c t i c i d e s , production practices and available equipment require that they be used i n this way. Ideally viruses should be used i n a manner that f a c i l i t a t e s their dispersal potential and epizootic development within and between generations of the insect host. Where cropping practices and pest population size allow t h i s , v i r a l pesticides have been more successful (30, 31). Timing of Application V i r a l insecticides are slow-acting agents that are not very effective against older, more damaging larvae. Applications must be c a r e f u l l y timed so that mortality occurs while larvae are small. Timing may d i f f e r , however, i f older larvae are more exposed during feeding than small larvae, as is the case with eastern spruce budworm, Choristoneura fumiferana i n forests of North America (31). Foliage feeding larvae are the most l i k e l y candidates for control with v i r a l insecticides (10, 31). Helicoverpa zea NPV has been used with some success against heliothine species, foliage and f r u i t feeders, on cotton. This is because application can be timed against small larvae that often feed on the upper terminals ( i . e . foliage where they are exposed to spray deposits). When a v i r a l insecticide is applied against a subeconomic populat i o n for control of succeeding generations, i t may be desirable to direct the application to larger larvae. The quantity of polyhe-



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dra produced i n v i r u s - k i l l e d cadavers w i l l increase with their size at death. Timing the application so that treated larvae are large at death w i l l result i n higher deposits of v i r a l inoculum against the target generation of the pest population. Timing virus applications to control future generations or i n succeeding years i s more p r a c t i c a l against foliage feeders on perennial crops such as i n forest situations (31). Proper timing of v i r a l insecticides is c r i t i c a l for their efficaceous use on crops. Much of the v a r i a t i o n i n efficacy i n f i e l d tests can be attributed to improper timing (usually late) of the application. In many instances proper timing could mean treating when the target population is predominantly eggs and newly hatched larvae. Effective application timing requires a more extensive (and expensive) scouting program than is t y p i c a l l y used for chemical insecticides. On some crops with high damage thresholds, where thresholds do not e x i s t , or i n areas where pest populations seldom reach economical l e v e l s , systematic survey programs rarely e x i s t . Furthermore, insect control l i t e r a t u r e may recommend that i n s e c t i c i d a l application be applied against large larvae. V i r a l insecticides are not l i k e l y to be effective i n these systems where early population detection and application cannot be assured. V i r a l insecticides k i l l slowly and result i n lower mortalit i e s than chemical insecticides in most instances. This often dictates that virus application be directed against pest populations of lower density than would be necessary for chemical insecticides. The lower levels of control obtained and the short residual period of v i r a l insecticides may also require that virus treatments be timed closer together and applied more often than for chemical insecticides. Because v i r a l insecticides are less effective than chemicals i n producing quick r e s u l t s , they are less l i k e l y to control high population densities of the target population. Because producers are accustomed to evaluating the effectiveness of the fast-acting chemical insecticides, they find i t d i f f i c u l t to delay their evaluation of virus application for the several days or even weeks often required for treated larvae to die (31). I f not properly trained, users may switch to chemical insecticides prematurely and never r e a l i z e that the virus would have been efficaceous. Methods of Application Application Equipment. For the most part equipment cost and a v a i l a b i l i t y dictate that v i r a l insecticides be applied with equipment designed for chemical insecticides. Accordingly, most research on application of v i r a l insecticides has been with this equipment. In e a r l i e r years some dust equipment was available, but at present viruses are applied as concentrated sprays from ground or a i r application equipment, whether applied as sprays, dusts or granules, the use of equipment developed for contact chemical insecticides does not appear capable of providing the desired coverage needed for the viruses. Virus must be deposited at feeding sites of the target pest so that i t can be ingested. This may require a method of application that directs the spray to


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areas of the plant canopy that can not be reached using convent i o n a l equipment. The parameters necessary for application of v i r a l insecticides are not well understood (12). F i e l d t r i a l s i n which viruses are formulated as dusts or granules have been l i m i t e d . Results of these tests have often been discouraging as efficacy of viruses formulated as dusts or granules is less than that of spray formulations (10). A i r vs. Ground Application Equipment. Ground spray equipment is the method of choice for testing v i r a l insecticides i n f i e l d crops. It is readily available and lends i t s e l f well to use i n small p l o t s . With both a i r and ground equipment, a boom-type sprayer with f l a t fan or hollow-cone nozzles i s often used. For control of forest pests, v i r a l insecticides are t y p i c a l l y applied by a i r , although control is generally superior when ground equipment is used i n young plantations, parks, beside roads, etc. (31). High pressure spray equipment is more l i k e l y to be used to apply virus i n f r u i t and vegetable IPM programs. Application volume is normally similar to that used for chemical insecticides, 10 to 47 1/ha and 19 to 114 1/ha for a i r and ground, respectively. Higher spray volumes generally increase coverage and efficacy, although there are exceptions (10, 30, 32). Use of high spray volume is l i m i t e d primarily by the expense and time required to cover a given area (4). There is often a poor correlation between virus rate and efficacy i n tests i n the f i e l d (4, 31), suggesting that available application methods are not effective i n delivering the virus to feeding s i t e s of the target pest. The desired spray parameters may d i f f e r with target insect and crop. In situations where many individuals feed secluded, the concept of "good" coverage may d i f f e r from that commonly accepted for conventional chemical insecticides. It may be desirable to maximize virus deposits to control small larvae in more exposed sites while ignoring the remaining larvae, as any gain obtained from attempts to direct the spray to less exposed larvae could be small and not compensate for reduced control of exposed larvae. Existing application methods have been used most successfully with v i r a l insecticides against l a r v a l pests that feed on foliage i n the outer canopy (4, 30, 31). Unconventional Methods of Application. In addition to the convent i o n a l methods of insecticide application, several novel methods of virus delivery have been tested. Most of these were designed for long term population suppression by u t i l i z i n g the disease producing features of dispersal and epizootic development. Autodissemination of the virus by male moths contaminated with virus in baited l i g h t or pheromone traps has been demonstrated (33). The males i n turn contaminate the female g e n i t a l i a during mating and eggs are contaminated externally when layed. Hatching larvae eat the virus deposits on the eggshell and become infected. Honey bee, Aphis melliphora, p o l l i n a t o r s have been contaminated with H. zea NPV formulated as a dust while entering and leaving their hive (33). This virus was successfully dispersed into nearby clover f i e l d s and epizootics developed i n H. zea populations were subsequently observed. Chemigation application with i r r i g a t i o n water


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has been used to a p p l y the Spodoptera frugiperda NPV and H. zea NPV a g a i n s t t h e i r r e s p e c t i v e h o s t s on c o r n ( 3 5 ) . Although o f f e r i n g p o t e n t i a l f o r e f f i c a c e o u s use i n some systems the expense o f t h i s type o f a p p l i c a t i o n i s p r o h i b i t i v e i n many c r o p p i n g systems u n l e s s i r r i g a t i o n i s needed a t the time o f a p p l i c a t i o n .


Tank M i x t u r e s Much o f the e f f o r t on v i r a l i n s e c t i c i d e r e s e a r c h has been aimed a t the development o f a d j u v a n t s to improve e f f i c a c y . A l t h o u g h some e f f o r t has been d i r e c t e d a t i n c o r p o r a t i o n o f a d j u v a n t s i n t o the b a s i c f o r m u l a t i o n , a m a j o r i t y o f e f f o r t has been w i t h s p r a y tank adjuvants. M a t e r i a l s to overcome the p o t e n t i a l e f f i c a c y l i m i t i n g c h a r a c t e r i s t i c s o f the v i r u s ( e . g . s t a b i l i t y and coverage) have been t a r g e t s o f r e s e a r c h . Surface A c t i v e Agents. S u r f a c e - a c t i v e agents a r e most o f t e n added to tank m i x t u r e s . These may be e v a p o r a t i o n r e t a r d a n t s , s p r e a d e r s t i c k e r s and/or wetting agents. A wide v a r i e t y o f a v a i l a b l e commercial m a t e r i a l s are c o m p a t i b l e w i t h v i r a l insecticides, a l t h o u g h performance o f these agents i s not c o n s i s t e n t (9, 12). Sunlight Screens. The r a p i d i n a c t i v a t i o n o f v i r a l i n s e c t i c i d e s by the UV spectrum o f s u n l i g h t has l e d to the development o f s u n l i g h t s c r e e n s f o r use i n tank m i x t u r e s t h a t i n c r e a s e v i r u s p e r s i s t e n c e on the p l a n t . S h a d e ™ (Sandoz, I n c . ) and l i g n i n s u l f a t e are two e f f e c t i v e s u n l i g h t p r o t e c t a n t s most commonly used w i t h a p p l i c a t i o n s i n f o r e s t s and a g r i c u l t u r a l c r o p s (10, 31). Many o t h e r m a t e r i a l s c o m p a t i b l e w i t h v i r a l i n s e c t i c i d e s are e f f e c t i v e sunl i g h t s c r e e n s (13, 28). A l t h o u g h e f f e c t i v e as s u n l i g h t s c r e e n s , these m a t e r i a l s o f t e n do not s i g n i f i c a n t l y i n c r e a s e v i r u s e f f i c a c y (4, 31). The i n c r e a s e i n e f f e c t i v e n e s s o f L . d i s p a r NPV a g a i n s t L . d i s p a r l a r v a e observed with s t i l b e n e f l u o r e s c e n t b r i g h t n e r s does not appear to r e s u l t from t h e i r a c t i v i t y as s u n l i g h t s c r e e n s , s i n c e t h e s e c h e m i c a l s are a l s o e f f e c t i v e s y n e r g i s t s f o r the NPV i n l a b o r a t o r y assays (36). These f i n d i n g s suggest t h a t a g a i n s t many i n s e c t s , v i r u s p e r s i s t e n c e i s adequate a t the f e e d i n g s i t e s o f the t a r g e t i n s e c t , such as on u n d e r s u r f a c e o f l e a v e s , t e r m i n a l s , e t c . Furthermore, s i n c e s u n l i g h t s c r e e n s add expense to the c o s t o f a p p l i c a t i o n and a t h i g h e r c o n c e n t r a t i o n s i m p a r t u n d e s i r a b l e s p r a y q u a l i t i e s ( d i f f i c u l t to mix and s p r a y ) , i t may not be p r a c t i c a l i n many i n s t a n c e s to use them at the c o n c e n t r a t i o n s needed to p r o v i d e efficacious sunlight protection. Buffers: Because s o l u t i o n s o f h i g h i o n i c c o n c e n t r a t i o n s w i l l i n a c t i v a t e v i r u s , i t may be n e c e s s a r y to b u f f e r the t a n k - m i x t u r e . Some b u f f e r s may a l s o be n e c e s s a r y w i t h some a d j u v a n t s and where l o c a l water has an extreme pH. In a d d i t i o n , l e a f s u r f a c e chemic a l s may r e s u l t i n a h i g h pH l e a f s u r f a c e . C o t t o n l e a v e s have a s u r f a c e pH between 9 and 10 and have been shown to i n a c t i v a t e v i r a l i n s e c t i c i d e s a p p l i e d to the s u r f a c e . I n a c t i v a t i o n i s slow ( i n comparison to s u n l i g h t i n a c t i v a t i o n ) and does n o t appear to be i m p o r t a n t under f i e l d c o n d i t i o n s where o c c a s i o n a l r a i n f a l l o c c u r s (37).



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Gustatory Stimulants. The a d d i t i o n o f g u s t a t o r y s t i m u l a n t s to the tank m i x t u r e has been found to i n c r e a s e consumption o f v i r u s by some l e p i d o p t e r o u s l a r v a l p e s t s . These m a t e r i a l s appear to o f f e r p o t e n t i a l to i n c r e a s e e f f i c a c y o f v i r a l i n s e c t i c i d e s on c r o p s , p a r t i c u l a r l y i n s i t u a t i o n s where l a r v a e f e e d a t s i t e s where c o v e r age i s not a d e q u a t e . Most s t u d i e s have been c o n d u c t e d w i t h g u s t a t o r y s t i m u l a n t s o f h e l i o t h i n e s p e c i e s on c o t t o n . Host p l a n t e x t r a c t s and low c o n c e n t r a t i o n s o f sugars used a t r a t e s which i n c r e a s e v i r u s consumption i n the l a b o r a t o r y have seldom been e f f i c a c i o u s i n f i e l d t e s t s (4). Sugars a t h i g h e r c o n c e n t r a t i o n s ( o f t e n m o l a s s e s ) and more complex a d j u v a n t s t h a t have g u s t a t o r y s t i m u l a n t p r o p e r t i e s have sometimes p r o v e n to add to e f f i c a c y (20, 38). However, improvements may be caused by s e v e r a l o t h e r d e s i r a b l e c h a r a c t e r i s t i c s o f these a d j u v a n t s ( e . g . weak s u n l i g h t s c r e e n s , e v a p o r a t i o n r e t a r d a n t s , i n c r e a s e d d r o p l e t d e n s i t y , improve coverage, e t c . ) (20). When an i n c r e a s e i n e f f i c a c y o c c u r s i t i s d i f f i c u l t to determine which d e s i r a b l e p r o p e r t y ( i e s ) i s responsible. A complex a d j u v a n t , Coax (CCT C o r p . , L i t c h f i e l d P a r k , A Z ) , w i t h g u s t a t o r y s t i m u l a n t and o t h e r d e s i r a b l e p r o p e r t i e s i s a v a i l a b l e c o m m e r c i a l l y b u t expense p r o h i b i t s i t s use a t e f f e c t i v e r a t e s i n many IPM systems. Mixtures with other

Pesticides

An a r r a y o f p e s t i c i d e s may be a p p l i e d to most c r o p s d u r i n g the growing s e a s o n . C o m p a t i b i l i t y among p e s t i c i d e s i s i m p o r t a n t as i t i s o f t e n d e s i r a b l e a n d / o r n e c e s s a r y to t a n k - m i x p r o d u c t s s i m u l t a neously. T h i s i s p a r t i c u l a r l y t r u e f o r v i r u s i n s e c t i c i d e s because o f t h e i r e x t r e m e l y l i m i t e d h o s t r a n g e , e s p e c i a l l y when a p e s t complex i s p r e s e n t . V i r a l i n s e c t i c i d e s have been shown to be c o m p a t i b l e w i t h most c o n v e n t i o n a l c h e m i c a l i n s e c t i c i d e s such as p y r e t h r o i d s , organophosphates and carbamates (20, 39). V i r u s e s a r e t y p i c a l l y c o m p a t i b l e w i t h o r g a n i c p e s t i c i d e s w i t h low i o n i c c o n c e n t r a t i o n (near n e u t r a l p H ) . V i r u s e s have been t e s t e d i n combination with a v a r i e t y of i n s e c t i c i d e s for s y n e r g i s t i c a c t i v i ty. I n the l a b o r a t o r y , a c t i v i t y has been a d d i t i v e i n most i n s t a n c e s , w i t h s y n e r g i s t i c a c t i v i t y i n some i n s t a n c e s . In f i e l d t r i a l s , however, e f f i c a c y has seldom been o t h e r t h a n a d d i t i v e . M i x t u r e s o f v i r u s and Bacillus thuringiensis have been t e s t e d a g a i n s t s e v e r a l p e s t s i n the f i e l d w i t h s i m i l a r r e s u l t s (40). SUMMARY P r o d u c t i o n p r a c t i c e s and a v a i l a b i l i t y o f equipment r e q u i r e t h a t v i r a l i n s e c t i c i d e s be f o r m u l a t e d and a p p l i e d u s i n g t e c h n o l o g y designed for a p p l i c a t i o n of contact i n s e c t i c i d e s . Development o f f o r m u l a t i o n and a p p l i c a t i o n methodology f o r v i r a l i n s e c t i c i d e s has n o t p r o c e e d e d as r a p i d l y as a n t i c i p a t e d . Many v i r a l insecticides a r e e f f i c a c e o u s , b u t r e s e a r c h has slowed because few a r e m a r k e t e d . A l t h o u g h v i r a l i n s e c t i c i d e use i s l i m i t e d , t h e i r p o t e n t i a l f o r use i n IPM systems where o t h e r p e s t i c i d e s are not a v a i l a b l e o r d e s i r a b l e p r o v i d e s a window o f o p p o r t u n i t y f o r g r e a t e r use i n the f u ture. Improvements i n f o r m u l a t i o n and a p p l i c a t i o n t e c h n o l o g y


27.

YOUNG


393

designed for v i r a l insecticides are needed to help viruses reach their potential as commercial insecticides.

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4. 5. 6. 7. 8. 9. 10.

11.

12. 13. 14. 15. 16. 17. 18. 19. 20.

Payne, C. C. Parasitology. 1982, 84; pp 35-77. Saik, J . E . ; Lacey, L. Α.; Lacey, C. M. In Safety of Microbial Insecticides; Laird, M; Lacey, L. Α.; Davidson, E. W., Eds; CRC Press: Boca Raton, FL, 1989; pp 115-134. Doller, G. In Viral Insecticides for Biological Control. Maramorosch, K.; Sherman, Κ. Ε., Eds; Academic Press: New York, NY, 1985; pp 399-440. Yearian, W. C.; Young, S. Y. In Microbial and Viral Pesti cides; Kurstak, E . , Ed; Marcel Dekker: New York, NY, 1982; pp 387-424. Groner, A. In Safety of Microbial Insecticides; Laid, M.; Lacey, L. A.; Davidson, E. W., Eds; CRC Press: Boca Raton, FL, 1989; pp 135-148. Harper, J . D. In Epizootiology of Insect Diseases; Fuxa, J . R. and Tanada, Υ., Ed; John Wiley & Sons: New York, NY, 1987; pp 473-496. Podgwaite, J . D. In Viral Insecticides for Biological Con trol. Maramorosch, K.; Sherman, Κ. Ε., Eds.; Academic Press, Inc.: New York, NY, 1985; pp 775-797. Couch, T. L . ; Ignoffo, C. M. In Microbial Control of Pests and Plant Diseases, 1970-1980; Burges, H. D., Ed; Academic Press: New York, NY. 1981; pp 621-634. Yearian, W. C.; Young, S. Y. Misc. Publ., Entomol. Soc. Am, 1978, 10; pp 21-26. Young, S. Y.; W. C. Yearian. In The Biology of Baculoviruses Vol. II. Practical Application for Insect Control; Granados, R. R.; Federici, Β. Α., Ed.; CRC Press, Inc: Boca Raton, FL, 1986; pp 157-179. Falcon, L. A. In Proc. NSF-USDA-Univ. Fla. Workshop; Microbi al Control of Insect Pests: Future Strategies in Pest Manage ment Systems; Allen, G. E . ; Ignoffo, C. M.; Jaques, R. P., Eds; University of Florida: Gainesville, FL, 1978; pp 113-117. Smith, D. B.; Bouse, L. F. In Microbial Control of Pests and Plant Diseases, 1970-1980; Burges, H. D., Ed; Academic Press, New York, NY, 1981; pp 635-654. Jaques, R. P. Misc. Publ. Entomol. Sci. Am. 1977, 10; pp 99116. Hostetter, D. L . ; Bell, M. R. In Viral Insecticides for Biological Control. Maramorosch, K.; Sherman, Κ. Ε., Eds; Academic Press: New York, NY, 1985; pp 249-284. Ignoffo, C. M. J. Insect Pathol. 1964, 6; pp 318-326. Montoya, E. L . ; Ignoffo, C. M. J. Invertebr. Pathol.; 1966, 8; pp 251-254. Stacey, A. L . ; Yearian, W. C.; Young, S. Y. Ark. Farm Res; 1977, 2b; pp 3-4. McGaughey, W. H. J. Econ. Entomol. 1975, 68; pp 346-348. Ignoffo, C. M.; Batzer, O. F. J. Econ. Entomol.; 1971, 64; pp 850-853. Ignoffo, C. M.; Hostetter, D. L . ; Smith, D. B. J. Econ. Entomol., 1976, 69; pp 207-210.


394 21. 22. 23.

24. 25.


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RECEIVED April 30, 1993


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