Field Measurements of Pheromone Vapor Distribution - American

10 Field Measurements of Pheromone Vapor Distribution ALAN

W.

TAYLOR

Downloaded by PURDUE UNIV on August 28, 2014 | http://pubs.acs.org Publication Date: June 18, 1982 | doi: 10.1021/bk-1982-0190.ch010

U.S. Dept. of Agriculture, Beltsville Agricultural Research Center, Agricultural Environmental Quality Institute, Beltsville, MD 20705

Field measurements o f c o n c e n t r a t i o n s of d i s p a r l u r e in air under woodland p l o t s t r e a t e d w i t h three d i f f e r e n t slow r e l e a s e formulations showed that all r e l e a s e d pheromone f o r about one month: con c e n t r a t i o n s decreased about 80% in the first f i v e days and 90-98% over 35 days. Between 75 and 85% of the d i s p a r l u r e remained in the formulations a f t e r 35 days even though r e l e a s e had became very slow. Measurements w i t h other formulations c o n t a i n i n g t e t r a d e c e n o l formate a p p l i e d to corn showed these were more efficient but not p e r s i s t e n t enough to c o n t r o l Heliothis Zea f o r more than one month. No s a t i s f a c t o r y measurements o f c o n c e n t r a t i o n s in vapor plumes from p o i n t sources were p o s s i b l e even though these may be as e f f e c t i v e as b r o a d c a s t s . Further field research is l i m i t e d by sampling and a n a l y s i s techniques and the need f o r b e t t e r micrometeorological data. The o b j e c t o f t h e work d e s c r i b e d h e r e was t o measure t h e amount a n d d i s t r i b u t i o n o f pheromone v a p o r i n t h e a i r u n d e r woodland c a n o p i e s a f t e r a e r i a l a p p l i c a t i o n s o f slow r e l e a s e f o r m u l a t i o n s o f d i s p a r l u r e , and t h e r a t e a t which t h e s e d e c l i n e d w i t h t i m e . A l i m i t e d number o f e x p e r i m e n t s h a v e a l s o been done Z - 9 - t e t r a d e c e n o l f o r m a t e ( T D F ) , a m a t i n g i n h i b i t o r f o r t h e c o r n earworm moth ( H e l i o t h i s Z e a ) . I n a l l t h e e x p e r i m e n t s , d i r e c t measurements o f t h e concentrations o f thechemicals i n thea i r i n the treated p l o t s were made by d r a w i n g known v o l u m e s o f a i r t h r o u g h adsorbing samplers p l a c e d a t v a r i o u s h e i g h t s w i t h i n the plots. D e t a i l s o f t h e t r e a t m e n t s and s a m p l i n g p r o c e d u r e s v a r i e d somewhat f r o m e x p e r i m e n t t o e x p e r i m e n t a n d have b e e n d e s c r i b e d e l s e w h e r e (J_, 2, 3.» ^, 5 . ) : o n l y t h e more r e l e v a n t d e t a i l s w i l l be s u m m a r i z e d h e r e . S i n c e c u r r e n t a n a l y t i c a l This chapter not subject to U.S. copyright. Published 1982 American Chemical Society.

In Insect Pheromone Technology: Chemistry and Applications; Leonhardt, B., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

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procedures are not s e n s i t i v e enough to detect a e r i a l concentrations produced by a p p l i c a t i o n s of these chemicals at the r a t e s recommended f o r p o p u l a t i o n c o n t r o l , the r a t e s used i n the experiments described here were up to 500 g . a . i . / h e c t a r e , which i s about 25 times that used i n recommended p r a c t i c e . I t i s however b e l i e v e d that the r e s u l t s obtained can be d i r e c t l y e x t r a p o l a t e d downward to the lower rates.


Broadcast

A p p l i c a t i o n s of D i s p a r l u r e To Woodland

In an experiment i n woodland a t B e l t s v i l l e , Maryland, i n September 1979, three separate formulations were a p p l i e d by a i r to separate 4 hectare p l o t s (200 m χ 200 m). The t r e e s were between 15 and 20 meters high i n a dense stand of deciduous s p e c i e s with a few intermixed evergreens. The f i r s t p l o t r e c e i v e d 500 g.a.i./h of d i s p l a r l u r e as NCR g e l a t i n - w a l l e d microcapsules c o n t a i n i n g 2% a i . The formulation, a p p l i e d as an aqueous suspension, a l s o contained 1% o f s t i c k e r to a i d adhesion of the formulation to f o l i a g e . The second p l o t r e c e i v e d 500 g./h. as H e r c u l i t e Corporation sprayable laminate f l a k e s c o n t a i n i n g 9.1% a i . The f l a k e s c o n s i s t e d o f two l a y e r s of v i n y l , each 0.08 mm t h i c k on both s i d e s o f a c e n t r a l porous l a y e r c o n t a i n i n g the d i s p a r l u r e : the surface area of the f l a k e s was between 7 and 35 mm per s i d e . The same s t i c k e r as that i n the microcapsules was used. The t h i r d p l o t r e c e i v e d 330 g.a.i./h as "Conrel" c o n t r o l l e d r e l e a s e hollow f i b e r s c o n t a i n i n g nominally 11.5% a i . : a s u i t a b l e s t i c k e r was a l s o i n c o r p o r a t e d i n the f o r m u l a t i o n . (Note that the use of trade or p r o p r i e t a r y names here or elsewhere does not c o n s t i t u t e an endorsement by the USDA). 2

A i r samplers were mounted i n the center of each p l o t at 0.3, 2.0, 5.0 and 10 meters above ground. Samples were taken f o r consecutive 4 hour periods i n o v e r a l l 24 hour runs on a s e r i e s o f separate days up to 34 days a f t e r a p p l i c a t i o n . Samples o f the laminates and hollow f i b e r s were recovered from the p l o t s and analyzed f o r pheromone residues on s e v e r a l days. P e r s i s t e n c e A e r i a l concentrations are p l o t t e d as a f u n c t i o n of time f o r a l l three formulations i n Figure 1. Each curve shows the d e c l i n e i n c o n c e n t r a t i o n c a l c u l a t e d i n terms of the average a l l heights and sampling periods i n each 24 hour day. Rapid i n i t i a l d e c l i n e s were evident over the f i r s t few days i n both the microcapsule and f i b e r f o r m u l a t i o n s . A f t e r the tenth day, when average concentrations were between 5 and 10 ng/m^, a l l d e c l i n e d s t e a d i l y to between 0.4 and 2.0 ng/w? a f t e r about 30 days. S i m i l a r r e s u l t s , presented i n Table I, were obtained i n an e a r l i e r experiment i n which the same microcapsules were a p p l i e d at 250 g.a.i./h to a 20 m high canopy of deciduous



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DAYS IN FIELO Figure 1. Change in average concentration of disparlure in air under a deciduous woodland canopy treated in September 1979 with 3 slow release formulations: a) Conrel hollow fibers ( ); b) NCR microcapsules ( ); c) Hereon laminates ( ) (adapted from 1).


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Table I . Average D i s p a r l u r e concentrations during d a y l i g h t hours at 0.3 and 8.0 meters above ground under a woodland canopy t r e a t e d i n August 1976

Days a f t e r application

Concentration (ng/m3) at height


0.3

2 3 7 14 22 34

76 46 29 22 2 3 2

m

8.0

m

50 25 16 4 1 0.5

woodland at E l k Neck State Park, Maryland i n August, 1976 ( 2 ) . Although, as noted above, abnormally high a p p l i c a t i o n r a t e s were used i n these experiments i n order to ensure measurably high concentration i n a i r f o r the maximum time, the only d i f f e r e n c e between these and a p p l i c a t i o n s at the normal a p p l i c a t i o n r a t e s o f about 20 g. a i . / h was that the number of formulation p a r t i c l e s was g r e a t l y i n c r e a s e d . T h i s suggests that the data can be d i r e c t l y extrapolated downward to estimate a e r i a l concentrations i n p l o t s t r e a t e d at recommended r a t e s , i n d i c a t i n g t h a t , 30 days a f t e r treatment, these should be i n the range between 0.10 and 0.02 ng/m3 f o r the microcapsules, f l a k e s and f i b e r s . These are about the same order o f magnitude as the reported t h r e s h o l d concentrations f o r the response of many i n s e c t s to pheromones (6). It i s therefore d o u b t f u l that the e f f e c t i v e n e s s of these formulations i s l i k e l y to be more than about 5 weeks under c o n d i t i o n s s i m i l a r to those of these experiments. In warm summer weather e f f e c t i v e l i f e s p a n s might w e l l be l e s s . I t should be noted that while t h i s may be a s u f f i c e n t period f o r suppression of the mating of the gypsy moth which has a s i n g l e generation of i n s e c t s each year, and which i s s e x u a l l y a c t i v e over a l i m i t e d time p e r i o d , s i n g l e a p p l i c a t i o n s of these formulations may be q u i t e inadequate to produce pheromone vapor concentrations over the longer time periods necessary to c o n t r o l mating o f other i n s e c t species with f i e l d populations of a complex age s t r u c t u r e . P e r s i s t e n c e of formulations may a l s o be l e s s where they are a p p l i e d to shorter f i e l d crops which have a more v a r i e d microclimate than i n the r a t h e r s h e l t e r e d c o n d i t i o n s under a woodland canopy. The e f f e c t i v e n e s s of the formulation i n terms of the amounts of m a t e r i a l a p p l i e d can be evaluated i n terms of the


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Table I I .

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E f f e c t i v e n e s s of slow r e l e a s e formulations under f i e l d c o n d i t i o n s . Fibers

Flakes


Concentration In A i r Initial 30 days Decline D i s p a r l u r e Content of Formulation (%) Initial 30 days Fraction released

(ng/m3) 7.2 1.1 85*

22.5 0.4 98$

7.1 6.0

5.0

16%

24%

data presented i n Table I I . These show that, even a f t e r the pheromone emission from the p a r t i c l e s had ceased, very l a r g e f r a c t i o n s remained as unused and i n a c t i v e r e s i d u e s . Data suggesting a s i m i l a r l i m i t a t i o n on the e f f e c t i v e n e s s of the same microcapsule formulation were obtained i n an e a r l i e r f i e l d experiment ( 7 ) . The reasons f o r these d e c l i n e s i n emission from the formulations while they s t i l l c o n t a i n l a r g e f r a c t i o n s of the a c t i v e i n g r e d i e n t s are unclear, but they i n d i c a t e that d e t a i l e d study of the weathering process and t h e i r behavior i n f i e l d c o n d i t i o n s i s necessary to improve the e f f e c t i v e n e s s of t h e i r performance and reduce the amount of a c t i v e i n g r e d i e n t a p p l i e d and the number of a p p l i c a t i o n s that may be needed f o r long p e r i o d i n s e c t behavior c o n t r o l . Vapor D i s t r i b u t i o n The d i s t r i b u t i o n of vapors with height under the t r e a t e d canopy i s a complex f u n c t i o n of the d i s t r i b u t i o n of the formulation over the ground, the undergrowth and the canopy i t s e l f coupled with the mixing of the a i r by wind v e n t i l a t i o n and i n s t a b i l i t i e s of temperature g r a d i e n t s . Since however, turbulence i s much l e s s under the canopy of a l e a f y wood than i n an open f i e l d d i r e c t l y exposed to wind and r a d i a t i o n , comparison of vapor p r o f i l e s r e l e a s e d by d i f f e r e n t formulations during simular time periods w i l l give some i n d i c a t i o n o f any d i f f e r e n c e s i n the d i s t r i b u t i o n of the sources, although these i n d i c a t i o n s cannot be regarded as q u a n t i t a t i v e . Such a comparison of the vapor p r o f i l e s from the three formulations used i n the 1979 experiment are presented i n Table I I I . The most s t r i k i n g feature of these r e s u l t s i s the even d i s t r i b u t i o n of the vapor with height f o r a l l the formulations. As a broad g e n e r a l i t y the observation appeared true throughout the 24 hour p e r i o d s , no marked concentration g r a d i e n t s being found at any time. In comparisons between formulations the d i s t r i b u t i o n of the f i b e r s was most uniform. The r e s u l t s f o r the laminates are


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Table I I I . D i s t r i b u t i o n with height of average d i s p a r l u r e vapor concentrations r e l e a s e d from three formulations a p p l i e d to deciduous woodland at B e l t s v i l l e , Maryland i n 1979.

Height (meters)


10 5 2 0.3 periods averaged

Formulation Microcapsules Flakes (ng/m3) 14 a 5.2 ab 4.4 c 11 b 10 b 4.7 be 9.4 b 5.5 a 26

27

Fibers 9.8 8.7 8.7 10.6

a a a a

25

Within formulations, means followed by the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t at the 20% l e v e l (by Duncans M u l t i p l e Range T e s t ) .

ambiguous but do not i n d i c a t e any tendency f o r accumulation a t any p a r t i c u l a r h e i g h t . The data f o r the microcapsules s t r o n g l y suggests accumulation of the formulation on the f o l i a g e o f the canopy with somewhat smaller amounts on the ground and undergrowth. These data c o n t r a s t with those from the 1976 experiment presented i n Table IV. In these e a r l i e r data g r a d i e n t s of c o n c e n t r a t i o n are c l e a r l y evident, both i n these r e s u l t s and others not presented here. These g r a d i e n t s r e f l e c t the e f f e c t o f the lower d e n s i t y of the canopy i n the 1976 woodland p l o t i n two ways. The higher concentrations at the lower l e v e l s appear to r e f l e c t the g r e a t e r p e n e t r a t i o n o f the formulation to lower l e v e l s i n the thinner stand, r e s u l t i n g i n c o n s i s t e n t l y higher vapor concentrations c l o s e to the ground. Also the e f f e c t of increased wind v e n t i l a t i o n i n the thinner canopy i s c l e a r i n the data f o r the 15-17 hour sampling p e r i o d , where the higher r e l e a s e r a t e of the microcapsules caused an increased c o n c e n t r a t i o n c l o s e to the ground, while that at the 17 meter height f e l l due to increased v e n t i l a t i o n a s s o c i a t e d with g r e a t e r afternoon wind speed and turbulence. In general these r e s u l t s suggest that the character of the f o r e s t canopy w i l l prove to be one of the most important f a c t o r s c o n t r o l l i n g the d i s t r i b u t i o n of a e r i a l l y a p p l i e d slow r e l e a s e formulations under woodland canopies and the u l t i m a t e g r a d i e n t s of pheromone vapor under them.


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Broadcast A p p l i c a t i o n s o f Tetradecenol Formate To Corn The behavior o f two other formulations, microcapsules and small p l a s t i c laminate f l a k e s , c o n t a i n i n g t e t r a d e c e n o l formate, were compared i n a p p l i c t i o n s to p l o t s of mature corn at B e l t s v i l l e , i n August 1980. (8_) The Z-9-tetradecen-1-ol formate (TDF) i s a mating d i s r u p t a n t , r a t h e r than a true pheromone, of the H e l i o t h i s species o f moths. I t was s e l e c t e d i n these experiments because r e l i a b l e a n a l y t i c a l methods were a v a i l a b l e (JO and i t s behavior was expected to be s i m i l a r to that o f the a c t u a l pheromones, whose chemical s t r u c t u r e s and p r o p e r t i e s are a l s o s i m i l a r . The two formulations were polyurea-polyamide microcapsules 5-microns i n diameter supplied by ICI at B r a c k n e l l , B e r k s h i r e , England, and a small (3 mm side) p l a s t i c laminate formulation s u p p l i e d by the H e r c u l i t e Corporation o f York, PA. The microcapsules were a p p l i e d at 300 g of TDF per hectare and the f l a k e s at 285 g/h. Both formulations were a p p l i e d by a i r to mature corn 240-270 cm i n height i n c l e a r , hot weather with a d a i l y maximum temperature o f 39°C.

Table IV. Concentrations o f d i s p a r l u r e vapor between 0.3 and 17 meters height under a microcapsule-treated f o r e s t canopy at E l k Neck, Maryland, during d a y l i g h t hours on August 18, 1976. Time (EDT)

11-15 13-15 15-17 17-19

Concentration (ng/m^) at height (m)

0.3 "66 67 87 62

8.0 "58" 45 47 56

17.0 47 39 36 44

In order to measure the decrease i n r e s i d u e s , samples o f formulations were c o l l e c t e d by hand immediately a f t e r spraying and at approximately weekly i n t e r v a l s . The laminates were c o l l e c t e d by hand from p l a n t s u r f a c e s s c a t t e r e d through the p l o t . For the microcapsules, 16 12.5 cm f i l t e r paper c i r c l e s were l a i d together on a s i n g l e p l a s t i c sheet to r e c e i v e the spray. These were then c l i p p e d i n d i v i d u a l l y to p l a n t leaves at 150 cm height at a number of l o c a t i o n s throughout the p l o t . On each c o l l e c t i o n day, four f i l t e r papers were randomly c o l l e c t e d and i n d i v i d u a l l y analyzed to measure the decrease i n r e s i d u e s .



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Concentrations o f TDF i n a i r were measured at f i v e heights from 30 to 270 cm above the ground, using sampling and a n a l y t i c a l methods described elsewhere ( 9 ) . This sampling was done on days 3, 6, 10, 15, 21 and 31 a f t e r a p p l i c a t i o n : during each period o f 24 hours samplers were changed at 2200, 0000, 0200, 0600 and 1200 EDT. Wind speed g r a d i e n t s , a i r temperatures and temperature g r a d i e n t s were measured continuously. P e r s i s t e n c e The r e s u l t s presented i n Figure 2 show that the TDF residues disappeared from the laminates s u b s t a n t i a l l y f a s t e r than from the microcapsules. Expressed i n terms of f i r s t - o r d e r k i n e t i c s the h a l f - l i f e i n the capsules was 13.5 days and 5.3 days i n the laminates. The l a t t e r f i g u r e agrees w e l l with l a b o r a t o r y measurements of r e l e a s e r a t e s : these a l s o suggest that, i n t h i s formulation, the l o s s r a t e i s c o n t r o l l e d by d i f f u s i o n outward to the edges of the f l a k e s r a t h e r than through the e x t e r i o r l a y e r s of v i n y l c o v e r i n g . The changes i n average concentrations of TDF i n the a i r under the crop canopy between 2200 and 0200 EDT f o r each sampling day are p l o t t e d i n Figure 3· Since the s t a b i l i t y of the a i r i s g r e a t e s t at t h i s time, these values g e n e r a l l y represent the highest l e v e l s of the d i u r n a l c y c l e . They a l s o c o - i n c i d e with a c r i t i c a l time i n the f l i g h t and mating behavior of the H e l i o t h i s moths. Both formulations gave the highest night-time concentrations a f t e r being exposed i n the f i e l d f o r some time - the laminates a f t e r about 6 days and the microcapsules 15. I t may perhaps be s i g n i f i c a n t that both these correspond to the l o s s of about the same f r a c t i o n of r e s i d u e s , at times s l i g h t l y more than one residue h a l f - l i f e . The reason f o r the delay before the highest concentration, which was p a r t i c u l a r l y marked f o r the microcapsule formulation, cannot be explained on the b a s i s of changes i n a i r temperatures or wind speeds. One p o s s i b l e mechanism c o u l d i n v o l v e increases i n p e r m e a b i l i t y of the capsule w a l l s and laminates as the formulations weathered, leading to increased s p e c i f i c r a t e s of TDF r e l e a s e ( i . e . f l u x / u n i t weight TDF)_. This would l a t e r be o f f s e t by the decreasing amount of residue present. As an a l t e r n a t i v e , the e f f e c t of adsorption and desorption by s o i l and p l a n t l e a f s u r f a c e s may be considered. Studies of the adsorption and desorption of i n s e c t i c i d e and h e r b i c i d e vapors have c l e a r l y shown that these are h i g h l y s e n s i t i v e to water vapor and r e l a t i v e humidity. Similar organic molecules such as pheromones may perhaps be adsorbed during dry c o n d i t i o n s i n d a y l i g h t hours and released by r i s i n g humidity and dew formation at n i g h t , thus tending to s t a b i l i z e higher vapor concentrations under the s t i l l , moist canopy with s t a b l e a i r at n i g h t : i t may be noted that such a mechanism w i l l a l s o present a n a t u r a l l y s e l e c t i v e process f a v o r i n g the mating o f i n s e c t s that r e l e a s e n a t u r a l pheromones under such c o n d i t i o n s . Despite these questions of mechanism i t i s c l e a r


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10.

DAYS IN FIELD Figure 2. Decrease in residues of Z-9-tetradecenol formate in microcapsules ( ) and laminated flakes ( ) after field application to mature corn ($).


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Figure 3. Average concentrations of Z-9-tedradecenol-formate in air under mature corn between 2200 and 0200 EDT for 30 days after application of slow release laminate (X) and microcapsule (O) formulations (&).



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that the p l o t that received microcapsules was bathed i n s u b s t a n t i a l concentrations o f TDF vapor during the night hours f o r about one month, whereas the laminate t r e a t e d p l o t contained only very low l e v e l s a f t e r about two weeks: t h i s d i f f e r e n c e appears p r i m a r i l y due to the pattern o f r e l e a s e o f TDF from the formulations. E f f e c t i v e n e s s The two formulations used i n the TDF experiment d i f f e r e d from those i n the e a r l i e r d i s p a r l u r e experiment i n that the r e l e a s e o f the a c t i v e chemical d i d not cease u n t i l the residues were exhausted. I f the steady continuous r e l e a s e o f chemical over a period o f s e v e r a l weeks i s accepted as a c r i t e r i o n o f e f f e c t i v e n e s s , these formulations were c l e a r l y more e f f e c t i v e than those i n the d i s p a r l u r e experiment. Where broadcast a p p l i c a t i o n s o f pheromones are made to c o n t r o l i n s e c t behavior i n open, f r e e l y v e n t i l a t e d a g r i c u l t u r a l crops, a very l a r g e f r a c t i o n o f the pheromone released i s l o s t by d i r e c t d i s s i p a t i o n . Where, as i n the present case, the chemical i s being a p p l i e d to c o n t r o l the behavior o f n i g h t - f l y i n g i n s e c t s t h i s w i l l be p a r t i c u l a r l y true because only that f r a c t i o n released during night-time can be counted as e f f e c t i v e . Since no measurements o f f l u x r a t e s were made no d i r e c t estimate o f the amount l o s t i s p o s s i b l e , but i n d i r e c t estimates o f the amount required to permeate the a i r during the i n s e c t f l i g h t period can be made. A simple c a l c u l a t i o n shows that an average concentration o f 10 ng/m^ under the canopy o f 1 hectare o f crop with a height o f 2.5 m r e q u i r e s 250 micrograms. I f the average wind speed i s 1 m/sec (2 mph) t h i s must be replaced once per 100 seconds, corresponding to 54 mg/night f o r the period 2100 to 0300 hours. This i n d i c a t e s that over a 30 day period about 1.62 grams or 0.5$ o f an a p p l i c a t i o n o f 300 gr/hectare o f a c t i v e i n g r e d i e n t can be regarded as c o n t r i b u t i n g to i n s e c t mating c o n t r o l . While the f i g u r e s used i n t h i s c a l c u l a t i o n r e f l e c t the a r t i f i c a l c o n d i t i o n s used i n the experiments described, they i l l u s t r a t e a general p r i n c i p l e and suggest that l a r g e economies could be made i n the amount o f a c t i v e i n g r e d i e n t used by the development o f formulations that r e l e a s e i n response t o changes i n humidity or temperature depending on the release p a t t e r n d e s i r e d . Release From Point Sources In the l i g h t o f the poor e f f i c i e n c y o f broadcast a p p l i c a t i o n s o f pheromones i n a i r permeation techniques the a l t e r n a t i v e p r a c t i c e o f s c a t t e r i n g or p l a c i n g a l i m i t e d number of r e l e a s e p o i n t s a t s u i t a b l e distances apart over the t r e a t e d area merits c o n s i d e r a t i o n . Since each point w i l l then a c t as an i n d i v i d u a l source the t r e a t e d area w i l l be permeated by a set o f i n d i v i d u a l plumes o f pheromone vapor whose d i r e c t i o n w i l l vary with a i r f l o w through the crop or woodland. Large


INSECT


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concentration g r a d i e n t s may be expected from place to place w i t h i n the stand. Despite the d i f f i c u l t i e s o f sampling and data i n t e r p r e t a t i o n two experimental attempts were made to measure the average concentrations produced i n treatments of t h i s k i n d and the way i n which these d e c l i n e d with time. Neither produced meaningful data. I t was c l e a r that where i n d i v i d u a l sources each produce i n d i v i d u a l plumes with very high surrounding c o n c e n t r a t i o n g r a d i e n t s , sampling f o r two hour periods at p o i n t s downwind from such sources produces timeaveraged data that have l i t t l e p h y s i c a l meaning other than i n d i c a t i n g how long the source continues to g i v e out a d e t e c t a b l e plume. The problem i s w e l l i l l u s t r a t e d by measurements of TDF r e l e a s e from sources i n a 10 meter spaced g r i d of i n d i v i d u a l p o i n t s (Hereon p l a s t i c dispensers) i n a mature corn canopy 180-200 cm h i g h . Dispensers were at 108 and 180 cm h e i g h t s . Samplers at 30, 100 and 150 cm height, 1 meter downwind from a source, detected time average concentrations of 50 ng/m during the 2200-0200 hr p e r i o d on the s i x t h day a f t e r exposure. This f e l l to 9 ng by the 27th day. No d e t e c t a b l e amounts were found i n s i m i l a r samplers a t 7 m e q u i d i s t a n t from four separate g r i d sources. The data suggest a u s e f u l l i f e of 30-40 days f o r plume emission by these d i s p e n s e r s . A s i m i l a r experiment to measure d i s p a r l u r e r e l e a s e from sources mounted on a 25 m g r i d under a woodland canopy, which had proved e f f e c t i v e when evaluated by bioassay techniques measuring the mating o f tethered females, gave a wholly ambiguous r e s u l t i n that concentrations were below d e t e c t a b l e l e v e l s f o r the e n t i r e experiment. The negative character o f these r e s u l t s do not i n d i c a t e that the use of a l i m i t e d number of r e l e a s e p o i n t s i s b i o l o g i c a l l y a l e s s d e s i r a b l e p r a c t i c e , but r a t h e r that at the present time t h e i r e v a l u a t i o n by chemical methods r e q u i r e s sampling and a n a l y t i c a l techniques beyond those c u r r e n t l y a v a i l a b l e . T h i s i s indeed a p o i n t i n t h e i r favor, i n d i c a t i n g that, s i n c e they have been shown to be s u c c e s s f u l by b i o l o g i c a l techniques, t h i s success must r e f l e c t the g r e a t e r e f f i c e n c y with the smaller amounts o f pheromone i n j e c t e d i n t o the a i r . The use of a smaller number o f source p o i n t s a l s o permits a g r e a t e r degree of f l e x i b i l i t y i n the design of the formulations with more s o p h i s t i c a t e d r e l e a s e p a t t e r n s . 2

General

Conclusions

These experiments show that s e v e r a l formulations now a v a i l a b l e are s a t i s f a c t o r y f o r the permeation of a i r volumes i n woodland and crop canopies by pheromone vapors. Some formulations cannot however be regarded as e f f i c i e n t sources i n that they r e t a i n l a r g e f r a c t i o n s of the a c t i v e



10.

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Distribution

205

chemical a f t e r r e l e a s e has ceased. T h i s , coupled with the inherent i n e f f i c i e n c i e s of a i r permeation due to l o s s e s of chemical r e l e a s e d continuously over periods when i n s e c t s are i n a c t i v e , means that the amount of chemical used to confuse i n s e c t mating behavior i s a very small f r a c t i o n of that a p p l i e d . Improvement of t h i s e f f i c i e n c y presents a major research challenge f o r the f u t u r e . Although i n t u i t i o n suggests that point source r e l e a s e techniques may be more e f f e c t i v e , these methods are d i f f i c u l t to c h a r a c t e r i z e by p h y s i c a l measurements because of the low s e n s i t i v i t y of our a n a l y t i c a l methods and the d i f f i c u l t i e s o f sampling r e l e a s e plumes. In the immediate f u t u r e such methods can only be t e s t e d by d i r e c t measurements of e f f e c t s on i n s e c t behavior. We are a l s o unable at the present time to sample and analyze many pheromone chemicals at any c o n c e n t r a t i o n - l e t alone the low b i o l o g i c a l l y a c t i v e l e v e l s - because of t h e i r i n s t a b i l i t y upon the sampling media f o r the time they must remain t h e r e . Extension of our sampling and d e t e c t i o n and a n a l y s i s techniques to much lower l e v e l s presents another major research c h a l l e n g e . At the present time t h i s i s the main o b s t a c l e to progress. Beyond t h i s p o i n t i t i s p o s s i b l e to foresee the development of a major research area i n f u t u r e which w i l l c o n t r i b u t e to l a r g e s t r i d e s i n the techniques of c o n t r o l l i n g i n s e c t populations and i n s e c t behavior. In a d d i t i o n to the p o s s i b l e advances that w i l l r e s u l t from b e t t e r chemical c h a r a c t e r i z a t i o n of the d i r e c t e f f e c t s of pheromone or other s e m i o c h e m i c a l treatments, c o n t r i b u t i o n s from other d i s c i p l i n e s w i l l be e s s e n t i a l . An improved understanding o f the m i c r o m e t e o r o l o g i c a l c o n d i t i o n s i n which the i n s e c t s l i v e i s e s s e n t i a l both f o r an improved understanding o f how these a f f e c t the i n s e c t behavior i t s e l f , i n c l u d i n g the use o f the chemical communication systems they employ, and f o r improved understanding of the f a c t o r s that a f f e c t the r e l e a s e p a t t e r n s o f the formulations used. Too o f t e n the behavior o f the l a t t e r are evaluated and p r e d i c t e d i n l a b o r a t o r y systems which g r o s s l y o v e r s i m p l i f y the a c t u a l c o n d i t i o n s o f use. In p r a c t i c e , formulations are never used i n i s o l a t i o n but r e s t upon s o i l or p l a n t s u r f a c e s which are not passive but themselves respond to changes i n temperature, r a d i a t i o n , moisture and a i r flow. These changes, apart from d i r e c t e f f e c t s on the formulation are a l s o l i k e l y to cause changes i n the adsorption and d e s o r p t i o n of the vapors themselves, whether they are emitted e i t h e r by a c a l l i n g i n s e c t or by an a r t i f i c i a l f o r m u l a t i o n . In g e n e r a l , c o n d i t i o n s under crop canopies at n i g h t have r e c e i v e d l i t t l e a t t e n t i o n from a g r i c u l t u r a l c l i m a t o l o g i s t s who have concentrated p r i m a r i l y on the daytime e f f e c t s o f l i g h t , moisture and gas exchange because these are c l e a r l y o f g r e a t e r importance f o r the physiology of crop growth. As a



206

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consequence, not only our understanding of the nature of temperature, moisture and wind g r a d i e n t s w i t h i n crops during darkness i s more l i m i t e d , but the necessary instrumentation f o r measurement o f these i n the more s t a b l e and l e s s dynamic c o n d i t i o n s i s l a c k i n g . The i n v e s t i g a t i o n of these s u b j e c t s , emphasizing the c h a r a c t e r i z a t i o n of the micro-environment from the p o i n t o f view o f the i n s e c t i s l i k e l y to prove a h i g h l y f e r t i l e research area. Two c o n t r i b u t i o n s from other d i s c i p l i n e s are a l s o d e s i r a b l e . Improved use of pheromones and other semiochemic a l s w i l l depend upon a much b e t t e r understanding of the biochemical and physiochemical mechanisms w i t h i n the i n s e c t that produces them and upon which they a c t . Such systems are c l e a r l y complex and i t seems h i g h l y probable that, once they are understood, improved methods of i n h i b i t i n g them w i l l be found, i n c l u d i n g the p o s s i b l e uses of i n d i v i d u a l i n h i b i t o r y chemicals or c l a s s e s of them i n place of the a c t u a l pheromones themselves. F i n a l l y , improved techniques must be developed f o r b i o l o g i c a l assay o f the e f f e c t i v e n e s s o f management techniques f o r i n s e c t population c o n t r o l using semiochemicals. Since, i n the long run, the o b j e c t i v e of a l l pest management techniques i s the c o n t r o l o f populations, e v a l u a t i o n must be made using population growth and decay as a b a s i c s t a t i s t i c . Evaluation based upon trap catches and mating r a t e s i n small confined populations have u n c e r t a i n t i e s i n the s t a t i s t i c a l s i g n i f i c a n c e of the p r o j e c t i o n s based upon them that are so l a r g e that comparisons of the e f f e c t i v e n e s s of d i f f e r e n t treatments are not p o s s i b l e at the l e v e l required f o r progress. The development of improved techniques f o r measurements of population s i z e s and changes and the s t a t i s t i c s of t h e i r i n t e r p r e t a t i o n probably represents one of the major challenges not only i n the techniques discussed here but i n a l l other approaches and c o n t r i b u t i o n s to i n t e g r a t e d pest management methods o f i n s e c t c o n t r o l .


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Distribution

207

LITERATURE CITED 1. 2. 3· 4. 5.


6.

7. 8. 9.

Caro, J . H . ; Freeman, H . P . ; Brower, D. L.; Bierl-Leonhardt, B. A. J. Chem. Ecology 1981, 7, 867-880. Plimmer, J . R.; Caro. J. H . ; Freeman, H. P. J. Econ. Entom. 1978, 71, 155-157. Caro, J. H . ; Glotfelty, D. E.; Freeman, H. P. J. Chem. Ecology 1980, 6 229-239. Caro, J. H . ; B i e r l , Β. A . ; Freeman, H. P . ; Sonnet, P. E . J . Agri. Food Chem. 1978, 26, 461-463. Caro, J . H . ; Freeman, H. P . ; Bierl-Leonhardt, Β. A., J. Agri. Food Chem. 1979, 27, 1211-1215. Caro, J. H. Chapter in "Insect suppression with controlled release pheromone systems" Kydonieus, A. K. and Beroza, M. (Eds) 1980. CRC Press, Boca Raton, FL. Caro, J . H . ; B i e r l , Β. Α . ; Freeman, H. P . ; Glotfelty, D. E.; Turner, B . C. 1977. Environ. Entomol. 6, 877-881. Caro, J. H . ; personal communication. Caro, J. H . ; Freeman, H. P . ; Bierl-Leonhardt, Β. Α . , J. Agric. Food Chem. 1979, 27, 1211-1215.

RECEIVED February 24, 1982.


Field Measurements of Pheromone Vapor Distribution - American

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