Advances in Pesticide Formulation Technology - American Chemical

11 Development of an Aqueous-Based Controlled Release Pheromone-Pesticide System WILLIAM H. EVANS

Downloaded by CORNELL UNIV on October 7, 2016 | http://pubs.acs.org Publication Date: June 5, 1984 | doi: 10.1021/bk-1984-0254.ch011

Zoecon Corporation, Palo Alto, CA 94304

The state of the art of controlled released delivery systems in agriculture has advanced slowly in comparison with other areas of industry. This is especially true as compared to developments in the pharmaceutical industry. This situation has developed mainly due to the nature of the active ingredients and the associated high cost of the controlling system. Historically, agricultural chemical usage has been characterized by high dosage, low value and highly persistent active agents. Additionally, these actives must compete for market share with compounds of similar activity and price. In contrast, the pharmaceutical industry has had a distinct advantage by virtue of producing mainly low dosage, high value, non-persistent active agents. These agents are usually very specific in use and, thus, face much lower competition for market share. Also the nature of pharmaceutical applications is such that the chemicals are most effective when delivered at the action site in a controlled and precise rate. For these reasons, controlled release technology has been ideally suited for many applications in the pharmaceutical field. This is exemplified by the number of commercially available products and the new developments in basic research of biologically compatible controlled release drug delivery systems. It now appears that the trend in the agricultural industry is toward the development of highly active and target specific chemical agents. These types of chemicals are represented by the synthetic pyrethroids, insect growth regulators, anti-juvenile hormones and pheromones. These novel chemical agents are active at very low dosage rates and are usually highly labile to environmental conditions. Successful formulations of these agents must provide ample environmental protection and precision delivery of the active to the target species. In the light of these developments, controlled release delivery systems are gaining increasing emphasis in formulation design. This is no more evident than in the use of pheromones for the control of specific insect species in economically important crops. The utility of these biologically native, single target specific chemicals, has been realized 0097-6156/ 84/ 0254-0151 $06.00/0 © 1984 American Chemical Society

Scher; Advances in Pesticide Formulation Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

152

ADVANCES IN PESTICIDE FORMULATION TECHNOLOGY

only through the use of w e l l defined c o n t r o l l e d - r e l e a s e d e l i v e r y systems. C o n t r o l l e d - r e l e a s e pheromone systems have found use i n Inte grated Pest Management programs as i n s e c t monitoring t o o l s , i n mass trapping s t r a t e g i e s , and f o r mating d i s r u p t i o n by a i r permea t i o n . The l a t t e r technique has been modified so that the target species i s a t t r a c t e d by the pheromone to a t o x i c a n t source. This ' a t t r a c t i c i d e method o f f e r s the advantage of species s p e c i f i c e r a d i c a t i o n , without s i g n i f i c a n t i n t e r f e r e n c e to b e n e f i c i a l pred a t o r s . There are c u r r e n t l y s e v e r a l systems s p e c i f i c a l l y designed for i n s e c t monitoring and mass trapping techniques. Yet there are only two such systems that have been f u l l y commercialized f o r l a r g e acreage mating d i s r u p t i o n through a i r permeation, although s e v e r a l other systems are under development. The f i r s t system was introduced by Albany I n t e r n a t i o n a l ' s Conrel D i v i s i o n and c o n s i s t s of an impermeable hollow p l a s t i c f i b e r , sealed at one end and f i l l e d with a solvent s o l u t i o n of the pheromone( 1), Figure 1. The system obtains r e l e a s e by evaporation of the pheromone s o l u t i o n from the open end w i t h the pheromone d i f f u s i o n r a t e being depend ent upon the diameter of the f i b e r and the amount of pheromone i n i t i a l l y present. T h i s system has been shown to be u s e f u l f o r s e v e r a l pheromone types and has demonstrated i t s s u i t a b i l i t y f o r l a r g e acreage c o n t r o l of the Pink Bollworm, Pectinophora Gossyp i e l l a (Saunders), by mating d i s r u p t i o n . The second system was developed by the Hereon D i v i s i o n of Health Chem Corporation and c o n s i s t s of a laminated p l a s t i c c h i p , Figure 2 . The chip i s composed of a pheromone saturated polymer r e s e r v o i r w i t h a semi-permeable p l a s t i c membrane on e i t h e r s i d e . The pheromone i s thus r e l e a s e d by d i f f u s i o n from the r e s e r v o i r through the membrane. The r a t e i s c o n t r o l l e d by the membrane composition and thickness(2). The two systems are a p p l i e d i n a polybutene s t i c k e r to f a c i l i t a t e adhesion to the p l a n t surface. For a t t r a c t i c i d e a p p l i c a t i o n s , an appropriate p e s t i c i d e , u s u a l l y a s y n t h e t i c p y r e t h r o i d , i s added to the s t i c k e r base. A common disadvantage of these systems i s the need f o r s p e c i a l i z e d a p p l i c a t i o n equipment, which s i g n i f i c a n t l y l i m i t s the range of use of these systems. In the need f o r a more advanced system which would be s e l f c o n t a i n i n g i n pheromone and p e s t i c i d e , and o f f e r the d i s t i n c t advantage of conventional a p p l i c a t i o n , Zoecon Corporation sought to develop an aqueous based c o n t r o l l e d - r e l e a s e pheromonep e s t i c i d e system f o r a t t r a c t i c i d e a p p l i c a t i o n s . The requirements for a general formulation were the f o l l o w i n g :


1

ο ο ο ο ο ο

General system f o r d i f f e r e n t pheromone types, Aqueous based. Constant and c o n t r o l l a b l e r e l e a s e r a t e . Extend p r o t e c t i o n from degradation to pheromone. Contact t o x i c to i n s e c t species. Cost e f f e c t i v e compared to standard treatment.


EVANS

Controlled Release Pheromone-Pesticide System


11.

Figure

2.

Hereon Laminated

Chip


153

154



Matrix Development Release Rate Measurement A dynamic flow method was used to determine the r a t e of pheromone r e l e a s e from the v a r i o u s m a t r i c e s . A vacuum manifold was constructed f o r multi-sample a n a l y s i s . The sample chambers were modeled a f t e r the design of Cross(3) and c o n s i s t e d of a g l a s s chamber f i t t e d with a c h a r c o a l p r e - f i l t e r and absorbent column. The f o r m u l a t i o n samples were weighed onto g l a s s cover s l i p s and placed v e r t i c a l l y i n s i d e the sample chambers. The e n t i r e apparatus was held a t a constant temperature of 40.5 C. (105 F.) i n a walk-in hot room. A i r was continuously drawn through the sample chambers a t a constant r a t e of 1.5 l i t e r s per minute. Released pheromone was c o l l e c t e d on the columns, e l u t e d with solvent and analyzed by GLC. Recovery r a t e s were t y p i c a l l y > 95%. Formulation Development The i n i t i a l phase of the development was the determination of the r e l a t i v e s o l u b i l i t y of the s e l e c t e d pheromone, ZZ and ZE-7, 11hexadecadienyl acetate (Gossyplure, 1:1 r a t i o ) , i n a s u i t a b l e polymer matrix. Four d i f f e r e n t water-soluble or water-reducible r e s i n s were i n i t i a l l y i n v e s t i g a t e d : a water-soluble a c r y l i c mixture, two l a t e x emulsions and a n a t u r a l rubber c o l l o i d . I n t r i n ^ s i c s o l u b i l i t y was determined by making resin/pheromone s o l u t i o n s of v a r y i n g concentrations and measuring the r a t e of pheromone d i f f u s i o n from d r i e d f i l m s . In t h i s manner, we were able to determine the most s u i t a b l e base polymer from which to begin. The s o l u b l e a c r y l i c system o f f e r e d the most promise s i n c e the d i f f u s i o n p r o p e r t i e s could be e a s i l y v a r i e d by b l e n d i n g of d i f f erent molecular weight r e s i n s . Although composition of the p o l y mer base was e f f e c t i v e i n p a r t i a l l y c o n t r o l l i n g the r a t e of pheromone d i f f u s i o n , the d e s i r e d zero order r e l e a s e could not be obtained by t h i s technique alone. Therefore, the pheromone was pre-formulated i n t o a c o - s o l u b i l i z i n g o i l , thus c r e a t i n g a l i q u i d diffusion reservoir. By u t i l i z i n g an o i l that was m i s c i b l e with the pheromone and p a r t i a l l y s o l u b l e i n the r e s i n f i l m , an e f f e c t i v e d i f f u s i o n path was e s t a b l i s h e d . An emulsion of the o i l i n the aqueous r e s i n system was formed which r e s u l t e d i n the formation or a r e s i n coated o i l drop. The r e l e a s e r a t e c h a r a c t e r i s t i c s were g r e a t l y improved over the simple mixture of r e s i n and pheromone. The d i f f u s i o n p r o p e r t i e s of the f o r m u l a t i o n could be f u r t h e r modified by c r o s s - l i n k i n g of the r e s i n coat to form a permeable membrane. T h i s was accomplished by a d d i t i o n t o the aqueous phase of a m u l t i - f u n c t i o n a l b a s i c amine capable of c r o s s - l i n k i n g the r e s i n s at ambient temperature. Figure 3 shows the e f f e c t of these matrix v a r i a t i o n s upon the pheromone r e l e a s e r a t e . A small amount of h i g h l y a c t i v e s y n t h e t i c p y r e t h r o i d was next coated onto the membrane l a y e r . The system was completed by the i n c o r p o r a t i o r of spray m o d i f i e r s to i n c r e a s e the cohesiveness of the s o l u t i o n 'and to a i d i n d r o p l e t formation.



11.

EVANS


155

Upon spraying, the cohesive f o r c e of the s o l u t i o n causes drop l e t s of 3-5 mm diameter to be formed which are composed of up to s e v e r a l thousand of the o i l capsules per drop. As the formulation drys, the r e s i n c r o s s l i n k s forming a continuous membrane network surrounding the capsules. Due to e f f e c t s at the surface the i n t e g r i t y of the emulsion a t the i n t e r f a c e i s destroyed which thus leads to the formation of a r e s i n membrane surrounding the capsule network. A c r o s s - s e c t i o n of the system i s shown i n the photo micrograph i n Figure 4. T h i s system was found to r e l e a s e the pheromone a t a near zero order r a t e during the e f f e c t i v e l i f e t i m e of the formulation. The mechanism of r e l e a s e i s by d i f f u s i o n of the pheromone from the o i l s o l u t i o n through the membrane network. The d i f f u s i o n r a t e was found to be dependent upon the i n i t i a l pheromone c o n c e n t r a t i o n , the r e s i n / o i l r a t i o , and the degree of r e s i n c r o s s l i n k i n g . In each instance, the r e l e a s e c h a r a c t e r i s t i c s of the system were n e a r l y i d e n t i a l , that i s , the amount of the pheromone r e l e a s e d over time was constant. Thus by determining a s u i t a b l e matrix one could e a s i l y vary the parameters to o b t a i n the d e s i r e d magnitude of the r e l e a s e r a t e . Figure 5 i l l u s t r a t e s the consistency of the r e l e a s e charac t e r i s t i c s f o r an equivalent matrix where the only change i s the i n i t i a l pheromone c o n c e n t r a t i o n . The change i n the absolute r a t e for e q u i v a l e n t pheromone concentrations i s shown i n Figure 6, the m o d i f i c a t i o n here being the r e s i n to o i l r a t i o . Depending upon the d e s i r e d r a t e of pheromone r e l e a s e , the present system i s capable of constant r e l e a s e f o r up to three weeks under the s p e c i f i e d laboratory conditions. T e s t i n g and R e s u l t s In order to t e s t the e f f e c t i v e n e s s of the v a r i o u s matrix bases and t h e i r formulations, a wind tunnel b i o a s s y was performed i n co operation with researchers a t the USDA-Phoenix Research S t a t i o n . The bioassay chambers were constructed of 6.4 mm p l e x i g l a s s , 0.60 χ 0.60 χ 2.4 meters i n dimension. The a i r i n l e t end was f i t t e d with a c h a r c o a l f i l t e r through which a i r was drawn through the chamber by a v a r i a b l e v e l o c i t y f a n . The formulations to be tested were a p p l i e d to growing cotton p l a n t s and allowed to age for the d e s i r e d length of time. The t r e a t e d p l a n t s were p o s i t i o n ed a t the a i r i n l e t end of the chamber and the a i r f l o w adjusted to approximately 3-5 km/hr. Male pink bollworm moths were p o s i t i o n e d at the opposite end of the chamber, downwind of the pheromone source. Moth m o r t a l i t y was recorded versus an untreated c o n t r o l plant to compensate f o r any n a t u r a l m o r t a l i t y . Table I summarizes the data from the t e s t designed to demonstrate the ' a t t r a c t i c i d e ' e f f e c t . As can be seen, s i g n i f i c a n t m o r t a l i t y i s obtained only i n the case where pheromone and t o x i c a n t are both present.


156


s œ —Ι


Π3 CD

time F i g u r e 3.

Effect Δ

(hours)

of M a t r i x V a r i a t i o n s on Release Rate Resin Only Resin p l u s O i l C r o s s l i n k e d Resin plus O i l

RESIN MEMBRANE

O I L CAPSULES AND R E S I N NETWORK

F i g u r e 4.

Photomicrograph

of R e s i n / O i l Network

40x



11.

M

0

157


EVANS

I

I

I

J

I

I

I

1

F i g u r e 5.

I

I

J 2

M

I

I

I

J

I

I

I

I

3

I

I

I

I

I

I

4

I

ι 5

ι

ι

ι

ι

ι

ι

ι

ι

I

|

I

7

time (days) E f f e c t of Pheromone L e v e l on Equivalent Matrix ^ 750 ppm Pheromone - J - 500 ppm Pheromone

time

(hours)

F i g u r e 6. •

1

Β

E f f e c t of R e s i n : 0 i l Ratio f o r Equivalent Pheromone Concentration (750 ppm) R e s i n : 0 i l =1.0 Δ R e s i n : O i l =1.5


I

158


Table I .

A t t r a c t i c i d e Bioassy

Data

Formulation V a r i a t i o n

Ζ Mortality 24 h r .

with pheromone & t o x i c a n t w i t h pheromone only with t o x i c a n t only blank (no t o x i c a n t or pheromone)

32.0 0.7 4.0 0.0

48 h r . 81.4 4.7 6.0 1.3


a = s o l u b l e a c r y l i c base From t h i s stage, the most promising formulations were tested under n a t u r a l f i e l d c o n d i t i o n s f o r e f f e c t i v e n e s s and l o n g e v i t y of attraction. Since the most e f f e c t i v e pheromone emission r a t e was not known, nor the long term e f f e c t of the t o x i c a n t upon moth a t t r a c t i v e n e s s , a f i e l d trapping study was designed to determine the most e f f i c a c i o u s formulation. The s e l e c t e d formulations were a p p l i e d to growing cotton p l a n t s i n the f i e l d . D a i l y , a treated l e a f was placed i n a funnel type trap designed to capture l i v e moths(4). Table I I shows the formulation v a r i a t i o n s tested and the r e s u l t i n g moth catch. The r e s u l t s of t h i s t e s t were s i g n i f i cant i n that they c l e a r l y demonstrated the s u p e r i o r i t y of the s o l u b l e a c r y l i c system. A l s o i t was p o s s i b l e to determine an e f f e c t i v e f i e l d concentration of pheromone, i n the presence of t o x i c a n t , that would be a t t r a c t i v e and not d i s r u p t i v e to the male moths. [The e f f e c t s of the t o x i c a n t needed to be tested s i n c e i t had p r e v i o u s l y been reported that s y n t h e t i c p y r e t h r o i d s have r e p e l l e n t e f f e c t s on some species of moths.](5^ In c o n t r a s t to the l a b o r a t o r y data, the e f f e c t of the p y r e t h r o i d upon the cons i s tancy of the pheromone r e l e a s e i s evident. I t appears that i n outdoor exposure s i t u a t i o n s the chemicals are instrumental i n the s t a b i l i z a t i o n of the pheromone or i n the mediation of i t s r e l e a s e . Results and D i s c u s s i o n On the b a s i s of l a b o r a t o r y and f i e l d r e s u l t s , the s o l u b l e a c r y l i c system was chosen f o r f u r t h e r f i e l d t r i a l s . The formulation (code //1692) was t e s t e d on 210 hectares, 13 separate f i e l d s i n Arizona and C a l i f o r n i a during the 1982 growing season. Each t e s t f i e l d was compared to a standard f i e l d , treated e i t h e r with a chemical regime or a commercial pheromone product, l o c a t e d i n the immediate vicinity. The e f f i c a c y assessment was based on trap catch r e d u c t i o n and b o l l i n f e s t a t i o n c o n t r o l . The treatment r a t e was 6.9 l i t e r s of formulation per hectare. T h i s represented a r a t e of 3.7 grams pheromone and 36.9 grams p y r e t h r o i d per hectare. Treatment i n t e r v a l s were approximately ten days apart and the a p p l i c a t i o n s


11.

EVANS



Table II.

Pink Bollworm Field Trapping Data

Formulation Base

Toxicant

Acrylic Emulsion

Permethrin

If

If

II tt

It

ft

It

tt

It

tt

tt

II

Soluble Acrylic

ft

Mavrik

Permethrin

If

II

ft

II

II

It

tt

It

tt

tt

11

II

159

ft

Mavrik

%

% Pheromone

a

Average Catch per day

0.60 0.60 0.40 0.40 0.50 —

0.075 0.040 0.075 0.040 0.040 0.075

21.5 11.4 28.4 13.8 16.6 12.7

0.60 0.60 0.40 0.40 0.50 —

0.075 0.040 0.075 0.040 0.050 0.075

37.4 28.1 36.0 28.7 21.1 19.1

Leaf Control

0.0

a = 15 day average

continued throughout the normal pink bollworm season. Figure 7 shows the e f f e c t of the formulation upon the trap c a t c h as compared to an untreated f i e l d . The data given i n Table I I I compares the treatment regimes on a f i e l d by f i e l d b a s i s . Unfortunately absolute comparisons to the current s t a t e of the a r t pheromone systems could not be made s i n c e i n a l l cases these f i e l d s were a l s o t r e a t e d with v a r i o u s chemical agents. However, the data can s t i l l be compared on o v e r a l l e f f i c a c y and performance. The compa r a t i v e data does i n d i c a t e that i n the m a j o r i t y of the cases the b o l l i n f e s t a t i o n l e v e l s were kept to below 5%, which would be considered the economic t h r e s h o l d l e v e l ( 6 ) . The data a l s o c l e a r l y demonstrates that a considerable r e d u c t i o n i n conventional p e s t i c i d e usage can be achieved by use of t h i s system. I t i s important to note that i n s e v e r a l t e s t s the percent i n f e s t a t i o n i n comparable f i e l d s i s c o n s i d e r a b l y higher than the acceptable t h r e s h o l d l e v e l . T h i s data e x e m p l i f i e s one of the more s e r i o u s d e f i c i e n c i e s of pheromones when used as chemical c o n t r o l agents. Many i n v e s t i gators have found that pheromones are most e f f e c t i v e a t r e l a t i v e l y low to moderate population pressures, and tend to be h i g h l y i n e f f e c t i v e a t p o p u l a t i o n d e n s i t i e s above a c e r t a i n threshold(7) . Thus the u t i l i t y of pheromone usage may be more compatible with Integrated Pest Management p r a c t i c e s .


160



CD —1

date: June 1982 Figure

7.

Trap

Catch Comparison; T r e a t e d v s Untreated • Pheromone T r e a t e d a t ^ Δ Untreated


Field


= = = =

%

5.3 1.7 13.4 1.3 2.5 0.0 0.0 0.4 33.0 2.4 0.0 1.0 0.2

Infested bolls d

183.47 122.31 183.47 61.16 122.31 122.31 142.70 163.09 101.93 101.93 122.31 122.31 163.09

Cost: $ per hectare 13 7 13 7 6 6 3 3 11 3 3 3 3 a

5b

-5^

5a 3b

-5

_

c

-

3

3

-c

Nomate

Reference P l o t

No. o f A p p l i c a t i o n s Hereon Insecticides

Trials

Hereon D i v . , NY, NY; f l a k e s c o n t a i n i n g pheromone + P y d r i n Hereon D i v . , NY, NY; f l a k e s c o n t i n i n g pheromone + Ambush C o n r e l D i v . , Needham, MA; f i b e r s c o n t a i n i n g pheromone R e p r e s e n t s t o t a l chemical c o s t . A p p l i c a t i o n cost not i n c l u d e d .

9 6 9 3 6 6 7 8 5 5 6 6 8

215 216 217 220 221 223 218 219 222 224 225 226 227

a b c d

No. o f Appl. Zoecon

Test P l o t

E f f i c a c y Comparison f o r 1982 F i e l d

Test no.

Table I I I .


%

16.4 2.2 20.2 2.0 0.8 2.3 1.4 0.4 13.0 0.0 0.0 3.8 1.5

Infested bolls

d

162.47 92.29 166.52 126.61 78.43 96.02 93.97 93.97 214.01 95.60 95.60 118.61 118.61

Cost: $ per hectare

A D V A N C E S IN P E S T I C I D E F O R M U L A T I O N T E C H N O L O G Y

162


Conclusion An aqueous based c o n t r o l l e d - r e l e a s e pheromone system was developed f o r c o n t r o l of i n s e c t s p e c i e s i n l a r g e acreage f i e l d crops. The system was shown to be e f f i c a c i o u s f o r the c o n t r o l of the pink bollworm, when compared to standard i n s e c t i c i d e usage and s t a t e ot the a r t s o l i d r e l e a s e m a t r i c e s . The system has the d i s t i n c t advantage of being c o n v e n t i o n a l l y a p p l i e d and c o n t a i n i n g both pheromone and t o x i c a n t . The system a l s o allows a s i g n i f i c a n t r e d u c t i o n i n c o n v e n t i o n a l p e s t i c i d e usage, w h i l e l i m i t i n g b o l l i n f e s t a t i o n to l e v e l s comparable to standard chemical usage and s t a t e of the a r t pheromone systems. I t now remains to be seen i f the system can be adapted on a g e n e r a l b a s i s to the pheromones of other economically important i n s e c t s s p e c i e s .

Acknowledgments The k i n d e s t thanks to Dr. L o u i s B a r i o l a f o r conducting the b i o a s s y s t u d i e s . To Mr. David Rhoades f o r performing the r e l e a s e data measurements and Mrs. Marie Saunders f o r her i n v a l u a b l e a s s i s t a n c e w i t h the f o r m u l a t i o n development.

Literature Cited 1. Coplan et al., U.S. Patent 4 017 030, 1977. 2. Quisumbing, A. R.; Kydonieus, A. F., in "Insect Suppression With Controlled Release Pheromone Systems"; Kydonieus, A. F.; Beroza, Μ., Eds.; CRC Press: Boca Raton Fl., 1982; Vol, I, Chap. 8. 3. Cross, J. H. J. Chem. Ecol. 1980, 4, 781-787. 4. Lingren, L. J. Econ. Entomol. 1980, 73, 622-630. 5. Floyd, J. P.; Crowder, L. A. J. Econ. Entomol. 1981,74,634638. 6. "A Comparison of Pheromone, Pheromone and Pyrethroid and Insecticides for Control of the Pink Bollworm in the Imperial Valley, CA." USDA, 1981, Butler G. D. and Barker R. J. 7. Klassen, W.; Ridgway, R. L.; Inscoe, Μ., in "Insect Suppres sion With Controlled Release Pheromone Systems"; Kydonieus, A. F.; Beroza, Μ., Eds.; CRC Press: Boca Raton Fl., 1982; Vol. I, Chap. 2. RECEIVED February 9, 1984


Advances in Pesticide Formulation Technology - American Chemical

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