Pesticide Formulations - American Chemical Society

Chapter 17

Advanced Polymeric Systems for Site-Specific Release Control of Insecticides in Foliar Applications 1

Downloaded by UNIV OF MASSACHUSETTS AMHERST on September 21, 2015 | http://pubs.acs.org Publication Date: June 24, 1988 | doi: 10.1021/bk-1988-0371.ch017

Dieter Lohmann and Christian D'Hondt

Central Research Laboratories and Agricultural Division Ciba-Geigy Ltd., CH-4002 Basel, Switzerland

Chlordimeform (CDF), an i n s e c t i c i d e / a c a r i c i d e commonly used f o r foliar applications in cotton, as well as it's desmethyl analogue (CMF) have been converted into polymeric controlled release systems with tailored site-specific release c h a r a c t e r i s t i c s . Based on the microenvironmental conditions p r e v a i l i n g on cotton leaves, as the s i t e of the insects action and of the pesticides' application, a l k a l i - c a t a l y z e d hydrolysis, photolysis and cation exchange were employed t o trigger the release by cleavage o f susceptible chemical bonds connecting the active agents with a macromolecular c a r r i e r . Corresponding polymers com p r i s e ethyleneglycol carbamate and benzoin carbamate either as hydrolyzable o r light-sensitive spacer groups, o r they contain CDF bound as a s a l t to sulfonic acid groups i n the r e s i n . In vitro and in vivo investigations provide evidence f o r the benefits of the site-specific release p r i n c i p l e with respect to improved e f f i c i e n c y and safety o f pesticides i n practical use. In conventional applications o f pesticides c e r t a i n inherent loss factors can often r e s u l t i n a p a r t i a l l y useless waste of the chemicals and in t h e i r undesired d i s t r i b u t i o n to the environment and to non-target animals. In recent years controlled release systems based on the use of polymers have shown a considerable potential to overcome those disadvantages and r i s k s (1-17). With respect to agrochemicals the current controlled release technology covers mainly three d i f f e r e n t approaches how t o govern the active agents' b i o a v a i l a b i l i t y in crop protection. The pesticide can be p h y s i c a l l y dissolved, adsorbed or dispersed i n a polymer matrix, i n order to control i t ' s release by d i f f u s i o n or by matrix erosion. Current address: International Research Laboratories, Ciba-Geigy Ltd., 665 Takarazuka, Japan 0097-6156/88/0371-0208$06.00/0 ° 1988 American Chemical Society

P.O.

Box 1,

In Pesticide Formulations; Cross, B., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

17.

LOHMANN AND

D'HONDT

Release Control of Insecticides

209

- The p e s t i c i d e can be p h y s i c a l l y entrapped in polymeric reservoir systems, such as microcapsules hollow f i b e r s etc., i t ' s release i s regulated by permeation, osmosis or evaporation.


- The p e s t i c i d e can be chemically bound to macromolecular c a r r i e r s , e i t h e r as part of the polymer backbone or as a pendent moiety, and i t ' s release i s governed by the cleavage of susceptible chemical bonds. A large v a r i e t y of d i f f e r e n t polymers and copolymers has been used in numerous devices of various forms and dimensions. The main goal in the development of a l l those c o n t r o l l e d release p e s t i c i d e systems has so f a r been the r e l i a b l e control of the active ingredient's release rate, in order to keep i t ' s temporal b i o a v a i l a b i l i t y at a constant optimum l e v e l . The l o c a l i z e d release control by targeting the pesticide's d e l i v e r y s p e c i f i c a l l y to the p a r t i c u l a r pest or crop has hardly been drawn any attention to, although targeting of drugs i s an established and i n t e n s i v e l y studied subject in the pharmaceutical f i e l d (18). Our own research in t h i s f i e l d has been focussed on the achievement of additional s i t e - s p e c i f i c i t y in the release control of i n s e c t i c i d e s . It i s the aim of t h i s paper to shortly review some of the work accomplished or presently in progress within our laboratory. Concepts and Objectives f o r S i t e - s p e c i f i c Release Control in Cotton The most distinguished c h a r a c t e r i s t i c of s i t e - s p e c i f i c release control i s the f a c t that the release of a bioactive material i s in p a r t i c u l a r triggered and governed by a s p e c i f i c phenomenon occurring in the target biosystem. Regarding the three fundamental approaches to release control by polymers we came to the conclusion that a chemically bound system only implies a dimension of a c t i v a t i o n energy, which meets the requirements f o r the high s e l e c t i v i t y in the p e s t i c i d e release aimed at. Accordingly the general model of a polymeric s i t e - s p e c i f i c p e s t i c i d e relase system i s thought to be composed of a polymeric backbone containing comonomers and/or c r o s s l i n k i n g agents besides a monomer connected with the pendent p e s t i c i d e molecule (Figure 1). Whereas the components of the polymer chain should enable a c e r t a i n fine-tuning of the release c h a r a c t e r i s t i c s , the key p o s i t i o n in the system i s hold by a t a i l o r e d spacer group and a susceptible bond l i n k i n g the p e s t i c i d e to the polymeric c a r r i e r . Both these elements f i n a l l y determine mechanism, rate and s e l e c t i v i t y of the release process. N - ( 4 - c h l o r o - o - t o l y l ) - N N dimethyl-formamidine J_, (Chlordimeform, CDF), has been selected as a model p e s t i c i d e f o r f e a s i b i l i t y studies on the s i t e - s p e c i f i c release concept. CDF i s an i n s e c t i c i d e / a c a r i c i d e commonly used in f o l i a r applications to f i g h t pests in cotton e.g. spodoptera l i t t o r a l i s , h e l i o t h i s and others (19). Unfortunately Chlordimeform lacks a s u i t a b l e functional group which could be u t i l i z e d f o r the chemical binding to a polymeric c a r r i e r . The corresponding monomethyl compound, N -(4-chloroo-tolyl)-Nl methylformamidine 2 (CMF), usually referred to as N-Desmethyl-chlordimeform, shows an i d e n t i c a l spectrum of b i o l o g i c a l 2

1

1

2


210

PESTICIDE FORMULATIONS: INNOVATIONS A N D D E V E L O P M E N T S

a c t i v i t y and i s i n f a c t the a c t i v e form of J_ generated in vivo by demethylation (20, 21).

CMF


CDF

2

Due t o t h e r e a c t i v e secondary amino group CMF 2 was used in t h i s study f o r t h e synthesis o f those systems which imply the covalent binding to a macromolecule. CDF 1 was used f o r systems based on heteropolar linkages to polymers, aricl in bioassaying experiments i t was employed as a standard f o r comparision. With respect t o s i t e - s p e c i f i c i t y i n t h e release a d e t a i l e d knowledge of the biosystem one i s going to deal with, i s by a l l means an i n e v i t a b l e requirement f o r t h e r e a l i z a t i o n o f the targeting p r i n c i p l e . With CDF 2 actual target i s of course the insect which destroys leaves aricJ seed capsules of the cotton plant. Since these i n s e c t i c i d e s are a c t i v e against quite a v a r i e t y of insect pests in cotton, a general alignment of the release t r i g g e r with the metabolism of a l l these insect species was regarded as not f e a s i b l e . Therefore we have directed our search f o r possible t r i g g e r i n g e f f e c t s to t h e cotton leaf as the s i t e where the insects' eggs, larvae and adults appear. Consequently a s p e c i f i c property in the cotton l e a f ' s microenvironment was t o be u t i l i z e d as a s p e c i f i c release t r i g g e r . However, checking t h e microenvironmental conditions p r e v a i l i n g on cotton leaves resulted i n three d i f f e r e n t phenomena (Figure 2) probably employable f o r release t r i g g e r i n g by cleavage of chemical bonds according to the basic idea: a n d C M F

2 t h e

- pH values in the range of 8-10 existent on the leaf surfaces caused by a l k a l i n e excretions (22) - the optimum o r i e n t a t i o n of the leaves to sunlight with i t ' s photochemical potency - cation concentrations leaf dew (23).

o f 18-20 m moles/ltr. found in cotton

As a consequence a l k a l i - c a t a l y z e d hydrolysis, photolysis and cation exchange have been i d e n t i f i e d as the most promising t a r g e t - s p e c i f i c t r i g g e r s t o be u t i l i z e d in the new s i t e - s p e c i f i c release systems. Synthesis of Polymer-Bound Insecticides The f i r s t approach based on hydrolysis as a release mechanism required as a weak link between the polymer backbone and the pendent i n s e c t i c i d e moiety a l a b i l e bond to be hydrolyzed in a desired way under the cotton leaves a l k a l i n e conditions. Previous investigations (24) with model compounds containing CMF 2 linked with a l i p h a t i c moieties v i a urea-, amide-, ester-, carbamate- and p h o s p h o n i t r i l i c amide bonds, had c o n c l u s i v e l y proven only the carbamate linkage to be



17.

LOHMANN AND D'HONDT

Figure 1.


211

General model f o r s i t e - s p e c i f i c c o n t r o l l e d release pesticides

Atmosphere

Soil Spher

Figure 2.

•

pH 8 - 10 / dew

•

1 8 - 2 0 mmoles cations /

•

optimum orientation

Itr. dew

to sunlight

Microenvironmental conditions p r e v a i l i n g on cotton leaves



212

PESTICIDE FORMULATIONS: INNOVATIONS AND DEVELOPMENTS

suitably hydrolyzed a t the pH value concerned. By reaction of 2-hydroxyethyl-methacrylate, phosgen and CMF 2 the CMF d e r i v a t i v e 3 is obtained which can subsequently be polymerized by r a d i c a l techniques to form homo- or copolymers (Scheme 1). The polymers thus obtained containing the ethyleneglycol ester unit as a spacer group and the carbamate moiety as a susceptible bond are in perfect accordance with the model lead structure (Figure 1). The homopolymer 4 and the more h y d r o p h i l i c 1:1 copolymer with N-vinylpyrrolidone TNVP) 5 were s e t to modest molecular weights favouring convential f o l i a r a p p l i c a t i o n by spraying. The second concept based on the idea of a p h o t o l y t i c cleavage of the susceptible bond as a release t r i g g e r required a s u i t a b l e photoresponsive spacer group. Among various model compounds including a number of photoremovable protecting groups (25-27) connected with CMF 2 by carbamate linkages, f i n a l l y the benzoin-carbamate of CMF 2 was Tound to undergoe the desired photofragmentation under formation of CMF (28). A corresponding polymeric system can be synthesized from 4-methacrylamido-benzoin 6 by reaction with the carbamoylchloride of CMF (24) and by r a d i c a l poTymerization of the monomer _7 thus obtained (Scheme 2 ) . The 1:1 methyl-methacrylate copolymer 8 and the corresponding N-vinyl-pyrrolidone copolymer 9 were adapted in the molecular weights t o the h y d r o l y t i c systems 4 and 5. A d e t a i l e d investigation o f the photochemistry of the monomeric and polymeric CMF-benzoin-carbamates using CIDNP-NMR techniques (29, 30) confirmed the -cleavage o f the benzoin moiety as an absolutely predominant process r e s u l t i n g i n the formation o f CMF, C 0 and 2-phenylbenzofuran moieties (Scheme 3). The t h i r d approach we were thinking o f i s based on the u t i l i z a t i o n o f the r e l a t i v e l y large c a t i o n concentration p r e v a i l i n g on cotton leave surfaces as a release t r i g g e r . Since Chlordimeform J[ is a weak base i t i s capable of forming stable s a l t s with strongly a c i d i c polymeric s u l f o n i c acids. Among various l i n e a r and c r o s s l i n k e d a l i p h a t i c and aromatic polymeric s u l f o n i c acids those CDF-resinates formed with sulfonated highly porous s t y r e n e / d i v i n y l benzene copolymers showed by f a r the most superior s t a b i l i t y and release capacity (Scheme 4). The release process of CDF could be simulated in v i t r o with spray deposits on f i l t e r paper obtained from aqueous formulations o f the products. Whereas a deposit obtained from conventional CDF emulsion concentrate (EC) i s completely depleted a f t e r 5 days due to CDF-evaporation, deposits obtained from the CDF resinate JO do not loose any a c t i v e agent f o r weeks. Subsequent spraying with d i s t i l l e d water has no influence. Only when increasing amounts of sodium bicarbonate are sprayed onto the CDF-resinate deposits there are gradually well-defined portions of CDF released and exposed to regular evaporation. The complete release of CDF from the resinate requires under these conditions almost 4 equivalents of cations (Figure 3). 2

Physicochemical and B i o l o g i c a l Properties of the S i t e - S p e c i f i c Controlled Release Systems Evaporation, wash o f f by r a i n , leaching and chemical degradation are among t h e most important loss f a c t o r s which often decimate a pesticide's b i o a v a i l a b i l i t y in open f i e l d a p p l i c a t i o n s within a short



17.

LOHMANNANDD'HONDT


£ HOMOPOLYMER

M ~ 7800

5 NVP-COPOLYMER ( 1:1 )

Scheme 1.

213

M - 7600

Hydrolytic systems: monomer synthesis and polymeri zation (NVP=N-vinyl-2-pyrrolidone)

7_

6.

SL MMA - COPOLYMER

( 1:1 )

9 NVP - COPOLYMER ( 1:1 )

Scheme 2.

M M

8300 8000

Photolytic systems: monomer synthesis and polymerization (MMA=methy1-methaerylate; NVP=Nvinyl-2-pyrrolidone)




214

CDF - LOADINGS : 30 - 36

Scheme 4.

%

Preparation of CDF-resinates



17.

Release Control ofInsecticides

LOHMANNANDD'HONDT

215

remaining deposit

% A

0

5

10

15 ****

Figure 3. CDF evaporation from CDF resinate spray deposits (CDF, dotted line: deposits from conventional CDF emulsion concentrate). (Reproduced with permission from ref. 31. Copyright 1987 Controlled Release Society.)



216


period of time. Table I summarizes some physicochemical properties of the three d i f f e r e n t types o f new c o n t r o l l e d release systems. In comparison t o CDF Jl and CMF 2 the polymers 4, 5, 8, 9 and _10 show a dicrease in vapour pressure aricl water s o l u b i l T t y by several orders of magnitude. In t h e absence of those t r i g g e r i n g influences which the respective design of the system i s based on aqueous formulations of the polymers e x h i b i t highly improved s t a b i l i t i e s and do not contain detectable amounts of f r e e CDF. Two days a f t e r a e r i a l applications in cotton plantations, CDF recoveries on the crop were determined to be 40-60 % increased when the new polymers were used compared to the conventional CDF emulsion concentrate. This r e s u l t exemplifies c l e a r l y the s u b s t a n t i a l l y reduced environmental losses obtained with the new s i t e - s p e c i f i c release systems - a f a c t o r of considerabel importance with regard to economical and e c o l o g i c a l aspects. A f t e r t h e f e a s i b i l i t y of the three d i f f e r e n t s i t e - s p e c i f i c re lease mechanism had been v e r i f i e d by simulating in v i t r o experiments, the new systems were to be tested on the real b i o l o g i c a l target under p r a c t i c a l conditions. In greenhouse experiments laboratory-reared spodoptera l i t t o r a l is larvae o f t h e f i r s t i n s t a r on young cotton plants (30 cm) were used f o r the bioassaying experiments. Larval m o r t a l i t i e s were assessed 4 and 8 days a f t e r treatment of the plants with wettable powder (WP)-, emulsion concentrate (EC)- or flowable (FO)-formulations o f t h e new polymers 4, 5, 8, 9, H). Some of the polymers were also tested i n f i e l d experiments and n a t u r a l l y occurring eggs and larvae were used f o r assessing the a c t i v i t i e s . The r e s u l t s (Table II) give evidence of the two photolytic systems (8, 9) as well as t h e CDF-resinate (10) being at l e a s t equal in TheTr i n s e c t i c i d a l potency to the standard CDF. EC- and FO-formulations are always more e f f i c i e n t than t h e corresponding WP-formulations, presumably due t o t h e i r favourable film-forming properties. The b i o a c t i v i t y o f t h e h y d r o l y t i c systems 4 and 5 i s found to be not completely s a t i s f a c t o r y . The lack of dew in greenhouse experiments - occurring every night in the f i e l d - might r e s u l t in an i n s u f f i c i e n t level of hydrolysis-triggered CMF-release. Further investiga tions require a c a r e f u l simulation of dew formation in greenhouse experiments and additional f i e l d t r i a l s under p r a c t i c a l conditions to give evidence o f t h e actual e f f i c i e n c y of the h y d r o l y t i c systems under p r a c t i c a l conditions. Since t h e aqueous formulations o f the new polymeric release systems do not contain d i s t i n c t amounts of f r e e CMF or CDF, the r e s u l t s from the bioassaying experiments provide c l e a r proof of the s i t e - s p e c i f i c release mechanisms conceived being e f f e c t i v e in the target biosystem. On t h e other hand due to the absence of f r e e i n s e c t i c i d e s t h e p r a c t i c a l formulations showed no t o x i c e f f e c t s during o r a l and dermal studies on r a t s . Thus s i t e - s p e c i f i c i t y of the release mechanism can contribute in a substantial way to handling safety and environmental clearance of p e s t i c i d e s . The forementioned environmental losses i n conventional applications o f p e s t i c i d e s lead t o i n s u f f i c i e n t duration of the p e s t i c i d a l a c t i v i t y . Therefore prolonged duration of a c t i v i t y i s another main goal advanced c o n t r o l l e d release systems aim at. A longterm a c t i v i t y t e s t with t h e polymers 5, 9 and JO has been performed in such a way that cotton plants in a greenhouse a f t e r the treatment with aqueous formulations of the polymers were stored f o r



Standards

CDF J_

CMF 2

CDF-Resinate H)

Ion Exchange

196

100

100

30

crosslinked

182

24

30

40

53

8000

8300

MMA-Copolymer (1:1) 8

NVP-Copolymer (1:1) 9

7600

7800

NVP-Copolymer (1:1) 5

Homopolymer 4

Systems

Photolyt.

Systems

Hydrolyt.

Controlled Release Polymer

CDF (CMF) Content % weight

250

350

«0,5

«0,5

«0,5

«0,5

« 0,5

Water Solubility 20°C ppm

7

«10"

3,6M0'

7,2M0"

7

7

«10"

«10"

7

7

«10"

«10"

4

5

Vapour Pressure 20°C mm Hg

Table I. Physiochemical Properties of Site-Specific Release Systems


2

2

H 0, 0 , l i g h t

sensitive to

stable i n absence o f cations

stable i n lighttight containers

hydrolytically stable a t pH 5 - 7,5

Stability


MMA-Copolymer (1:1) 8 NVP-Copolymer (1:1) 9

Photolyt.

44 66

WP-25 (4)

Standards

CDF 2

CMF 2 100

94

96

98

90

78

92 (F0)

97

100

98 (F0)

90

64 82

98

80 90

EC-50 (4) EC-50 (8)

% Larval M o r t a l i t y

Ion Exchange CDF-Resinate H) 92

Systems

Homopolymer 4 NVP-Copolymer (1:1) 5

Hydrolyt. Systems

Controlled Release Polymers

GREENHOUSE EXPERIMENTS

88 (EC)

-

larvae

72 (EC) 90 (EC)

76 (F0) 96 (F0)

-

43 (WP) 74 (WP)

eggs

% Mortality

FIELD EXPERIMENTS

Table II. Bioactivities of Site-Specific Release Systems (greenhouse experiments: Spodoptera littoralis larvae L I on cotton plants; field experiments: naturally occurring eggs and larvae of Spodoptera littoralis; WP=wettable powder, ED=emulsion concentrate, FO=flowable)



17.

LOHMANNANDD'HONDT


219

increasing periods o f time before i n f e s t a t i o n with spodoptera l i t t o r a l is larvae and assessment of the larval mortality. The r e s u l t s thus obtained from greenhouse experiments are shown in Figure 4. The photolytic NVP-copolymer 9 e x h i b i t s by f a r the highest duration of a c t i v i t y i n comparison t o the h y d r o l y t i c NVP-copolymer j>, t h e CDF-resinate 10 and the CDF standard. Under these conditions t h i s p a r t i c u l a r polymer keeps the i n s e c t i c i d a l potency on a high l e v e l o f 80-100 % f o r a period of four weeks compared to 10 days only found for the CDF standard. We assume that the minor e f f i c i e n c y of the polymer 5 and the CDF-resinate _H) observed in the longterm studies are again due to the f a c t that there i s water involved in the release processes concerned, hydrolysis and cation exchange. Under t h e influence o f dew in open f i e l d s the longterm a c t i v i t y of the l a t t e r systems might turn out more p o s i t i v e l y than the behaviour in the greenhouse. F i n a l l y i t was to be prooved that the photolytic systems, also containing carbamate linkages, not only in v i t r o (s. Scheme 3) but also i n vivo are subject t o the p a r t i c u l a r photoreaction under release o f CMF. For t h i s purpose a number of cotton plants was treated with aqueous formulations of the polymer 8. When the plants were stored under reduced l i g h t i n t e n s i t y in the shade the larval m o r t a l i t i e s found on those plants dropped to 15 % only within 10 days, compared to 98 % larval mortality a f t e r 10 days obtained with plants stored under f u l l daylight. With CDF used as a standard the larval m o r t a l i t i e s undergoe in both cases only the regular longterm decrease t o 76 % within 10 days. Based on these r e s u l t s , l i g h t i s considered t o be the actual release t r i g g e r in the polymer 8 thus confirming the f e a s i b i l i t y of the o r i g i n a l concept.

% larval mortality A100-

80-

60-

x

Hydrolytic NVP-Copolymer £

40-

}

CDF - Resinate 12

20-

4

Figure 4.

8

12

16

20

24 28 32 3 — - time ( d a y s )

Longterm b i o a c t i v i t y of s i t e - s p e c i f i c release systems (spodoptera l i t t o r a l is larvae L1, greenhouse, cotton plants 30 cm high)


220


Conclusions The new polymerbound c o n t r o l l e d release systems e x h i b i t s i t e - s p e c i f i c release c h a r a t e r i s t i c s , which are s p e c i f i c a l l y directed t o cotton leaves as a target biosystem. Hydrolysis, photolysis and cation exchange as release mechanisms can s e l e c t i v e l y be triggered under the biosystem s conditions. Reduced environmental losses and a general d e t o x i f i c a t i o n i s found as a benefit i n a l l the three systems. The preparation o f t h e new polymers includes r e l a t i v e l y simple and unexpensive processes, with the CDF resinate being at the head. Conventional formulation and spraying techniques can be used f o r the p r a c t i c a l a p p l i c a t i o n . Preliminary greenhouse and f i e l d experiments have given evidence o f t h e advantages o f s i t e - s p e c i f i c release systems. Expecially l i g h t - t r i g g e r e d release as a concept showed most promising r e s u l t s with respect t o a remarkably prolonged duration o f a c t i v i t y . Further investigations w i l l be directed t o the t r a n s f e r of the new concepts to various types of bioactive materials.


1

Acknowledgments The authors are g r a t e f u l t o Dr. G. R i s t f o r the NMR-spectrocopic investigation o f the photorelease mechanism and t o Dr. F. Bourgeois, F. Buholzer, Dr. V. Fluck, Dr. E. Neuenschwander and Dr. H. Schwitulla f o r the extensive b i o l o g i c a l t e s t i n g . L i t e r a t u r e Cited 1. G.G. A l l a n , C.S. Chopra, J.F. Friedhoff, R.I. Gara, M.W. Maggi, A. N. Neogi, S.C. Roberts, R.M. Wilkins, CHEMTECH. 1973 (3), 171 2. "Controlled Release Pesticides Formulations", edited by Nate Cardarelli, CRC Press, Inc., Cleveland, Ohio, 1976 3. "Proc. Controlled Release Pesticide Symposium", August 22-24, 1977, Corvallis, Oregon, edited by R.F. Goulding 4. "Controlled Release Technology-Bioengineering Aspects", edited by K.G. Das, John Wiley & Sons, New york, 1983 5. "Controlled Release o f Bioactive Materials", edited by R. Baker, Academic Press, New York, 1980 6. " B i o l o g i c a l Activities o f Polymers", edited by C.E. Carraher, C. G. Gebelein; ACS Symp. Ser. 1986, 13 (1981) 7. "Proc. Controlled Release Pesticide Symposium", Sept. 16-18, 1974, Akron, Ohio, edited by N.F. Cardarelli 8. A.N. Neogi, G.G. A l l a n i n "Advances i n Experimental Medicine and Biology", Vol. 47 edited by A.C. Tanquary, R.e. Lacey, Plenum Press, New York, 1974, p. 195-224 9. "Proc. Controlled Release Pesticide Symposium", Sept. 1975, Dayton, Ohio, edited by F. W. Harris 10. "Controlled Release P e s t i c i d e s " , edited by H.B. Scher; ACS Symp. Ser. 53, (1977) 11. "Proc. Controlled Release P e s t i c i d e Symposium", Aug. 1978, Gaithersburg, Maryland, edited by G.A. Montemarrano 12. "Controlled Release Technologies: Methods, Theory and Applications", Vol. 1 and 2, edited by A.F. Kydonieus, CRC Press Inc. Boca Raton, Florida, 1980



17.

LOHMANNANDD'HONDT


221

13. F.W. H a r r i s , A.E. Aulabaugh, R.D. Case, M.K. Dykes, W.A. Feld in "Controlled Release Polymeric Formulations", edited by D.R. Paul, F.W. H a r r i s ; ACS Symp. Ser. 33, 222 (1976) 14. "Proceedings of the 7th International Symposium on Controlled Release of Bioactive Materials", edited by D.H. Lewis, F t . Lauterdale, F l o r i d a , 1980 15. "Proceedings 12th Intl. Symp. Contr. Release Bioactive Materials", edited by N.A. Peppas, R. J. Haluska, July 1985, Geneva, Switzerland 16. "Proceedings of the 13th International Symposium on c o n t r o l l e d Release of Bioactive Materials", August 1986, N o r f o l k / V i r g i n i a , edited by J.A. Chaudry and C. Thies 17. "Proceedings of the 14th International Symposium on Controlled Release of Bioactive Materials", August 1987, Toronto/Canada, edited by P.J. Lee and B. Leonhardt 18. "Site-specific Drug Delivery", edited by E. Tomlinson and S.S. Davis, John Wiley & Sons, Chichester, 1986 19. "The Pesticide Manual" edited by C.R. Worthing, 7. edition, BCPC London 1985, p. 103 20. R.W. Beeman, Annu. Rev. Entomol 27, 262 (1982) 21. J.R. Corbett, K. Wright, A.C. B a i l l i e "The Biochemical Mode of Action of P e s t i c i d e s " , Academic Press, London, 1984, p. 167 22. J . J . Oertli, J . Harr, R. Guggenheim, J. Plant Dis. Prot. 84, 729 (1977) 23. S.Y. Young, W.C. Yearian, K.S. Kim, J . Invertebr. Pathol. 29, 105 (1977) 24. D. Lohmann, C. D'Hondt, Makromol. Chem. 188, 295-305 (1987) 25. E. Wuensch in "Methoden der organischen Chiemie" (Houben-Weyl) v o l . XV/1, edited by E. Wuensch, 4. edition, Georg Thieme, Stuttgart, 1974, p. 81-83, 150-153 26. V.N.R. Pillai, Synthesis 1980, 1-26 27. R.W. Binkley, T.W. Flechtner in "Synthetic Organic Photochemistry", edited by W.M. Horspool, Plenum Press, New York, 1984, p. 375-423 28. D. Lohmann in reference 16, p. 74 29. G.L. Closs, J . Amer. Chem. Soc. 91, 4552 (1969) 30. G.L. Closs, D.R. Paulson, J . Amer. Chem. Soc. 92 (24), 7229 (1970) 31. D. Lohmann, C. D'Hondt, in "Proceedings of the 14th International Symposium on Controlled Release of Bioactive Materials", August 1987, Toronto/Canada, edited by P. Lee and B. Leonhardt, p. 161, Figure 1 RECEIVED

January 11, 1988


Pesticide Formulations - American Chemical Society

Recommend Documents