Pheromone diffusion

The Initial phase of the development was the determination of the relative solubility of the selected pheromone, ZZ and ZE-7, 11-hexadecadlenyl acetate (Gossyplure, 1 1 ratio). In a suitable polymer matrix. Four different water-soluble or water-reducible resins were Initially Investigated a water-soluble acrylic mixture, two latex emulsions and a natural rubber colloid. Intrln- sic solubility was determined by making resln/pheromone solutions of varying concentrations and measuring the rate of pheromone diffusion from dried films. In this manner, we were able to determine the most suitable base polymer from which to begin. 

Another company (624, 625) supplies a controlled release dispenser, which is a three-layer plastic laminated sheet consisting of a bottom protective layer, a middle pheromone reservoir layer, and a top permeable layer through which the pheromone diffuses. The sheet can be cut into ribbons and applied over an area. Formulations have been field tested on a number of insect pests gypsy moth, pink bollworm, peachtree borer, lesser peach tree borer, soybean looper, cabbage looper, European elm bark beetle, tobacco budworm, fall armyworm, tussock moth, eastern spruce budworm, and Mediterranean fruit fly. 

The function of the male courtship pheromone in plethodontids was first documented in a study of Desmognathus ocoee Houck and Reagan (1990) showed that the diffusion delivery of a crude extract from the male pheromone gland increased... 

The demonstration of this behavioural response to a male pheromone signal is significant because of the manner in which the pheromone was delivered. Most other vertebrate examples of reproductive pheromones involve reception via the olfactory system(s). In contrast, D. ocoee females received the pheromone via diffusion through the dorsal skin. We assume that the well developed superficial capillary system of these lungless salamanders is the route by which the male pheromone was transported to whatever target tissue(s) initiated responses that affected female reproductive behaviour. 

The delivery of male courtship pheromones is widespread among plethodontid salamanders (Houck and Arnold 2003), and other courtship pheromones are being discovered for this group (Houck, Palmer, Watts, Arnold, Feldhoff and Feldhoff 2007). The mode by which these pheromones are transferred to the female apparently has been modified from delivery via diffusion into the circulatory system to delivery that directly stimulates vomeronasal receptors (Fig. 20.1 Houck and Sever 1994 Watts et al. 2004 Palmer et al. 2005 Palmer et al. 2007). The behavior patterns and morphologies associated with these two delivery modes often remain static for millions of years. In contrast, evolution at the level of pheromone signals is apparently an incessant process that continuously alters the protein sequence and composition of pheromones both within and among species (Watts et al. 2004 Palmer et al. 2005 Palmer et al. 2007). 

Pheromone propagation by wind depends on the release rate of the pheromone (or any other odor) and air movements (turbulent dispersion). In wind, the turbulent diffusivity overwhelms the diffusion properties of a volatile compound or mixture itself. Diffusion properties are now properties of wind structure and boundary surfaces, and preferably termed dispersion coefficients. Two models have dominated the discussion of insect pheromone propagation. These are the time-average model (Sutton, 1953) and the Gaussian plume model. 

Diffusion is the gradual dispersal of one substance through another substance, such as one gas through another gas (Fig. 4.20). Diffusion explains the spread of perfumes and pheromones, the chemical signals between animals, through air. It also helps to keep the composition of the atmosphere approximately constant, because abnormally high concentra-... 

The site of hydrocarbon pheromone production in the nitidulid beetles has been identified as very large, round abdominal cells, connected to the tracheal system by fine ducts (Dowd and Bartelt, 1993 Nardi et al., 1996). The secretory cells contain several lipid spheres (presumably pheromone and pheromone precursors), and are dramatically larger in beetles that are actively emitting pheromone (Nardi et al., 1996). Pheromone apparently diffuses from the cells,... 

Consider sensory hairs 2 pm in diameter that are 20 pm apart. Inserting these values into equation (21.22) and assuming that D is 2.5 x 10 6 m2/s (the diffusion coefficient for bombykol, the main component of the commercial silkmoth sex pheromone Adam and Delbriick, 1968) results in the prediction that these hairs are likely to interfere with each other s odorant interception when the air speed between the hairs is below 0.0125 m/s. This is not a discontinuous function - the sensory hairs will interfere with each other more at slower speeds and less at faster speeds. Another way of appreciating what this means quantitatively is to recognize that the root mean square displacement of a molecule (considering movement in one dimension) is... 

Futrelle R. P. (1984) How molecules get to their detectors the physics of diffusion of insect pheromones. Trends in Neurosci. 7, 116-120. 

The main use of PVC is for intravenous bags. However, PVC has been used in the controlled release of volatile insecticides, herbicides, pheromones, and perfumes by diffusion through a PVC membrane of multilaminated stripes. A monolithic matrix device of PVC can be prepared by mixing PVC particles with a suitable plasticizer and an active agent, followed by heating of the mixture in a mold. A solid PVC matrix is obtained from the subsequent cooling. 

The release of pheromone from hollow fibers as described by Brooks (6) is dependent upon several factors including the movement of air past the open end of the fiber. In the mini-airflow apparatus the open end of the fiber is in a stream of constantly moving air so that any released pheromone is immediately swept away from the end. In the static air apparatus the only air movement across the open end will be as a result of diffusion. Consequently the concentration of pheromone is more likely to build up at the open end of a fiber in a static air apparatus than at the open end of a fiber in an airflow apparatus with the result that the release rate is lowered in the static air apparatus. Work is now in progress to evaluate the effect of air speed on release rates. 

The emission from a controlled-release formulation is generally limited by a diffusion process which is controlled by the concentration gradient across a barrier to free emission and the parameters of the barrier itself (3). The rate of release follows approximate zero order kinetics if the concentration gradient remains constant i.e., the rate is independent of the amount of material remaining in the formulation except near exhaustion. A large reservoir of pheromone is generally used to attain a zero order release. Most formulations, however, tend to follow first order kinetics, in which the rate of emission depends on the amount of pheromone remaining. With first order kinetics, In [CQ/C] = kt where CQ is the initial concentration of pheromone, C is the residual pheromone content at time t, and k is the rate of release. When C 1/2 CQ, the half-life, of the formulation is 0.693/k. Discussions of the theoretical basis for release rates appear elsewhere (4- 7)... 

The emission of a pheromone from a controlled-release formulation can depend on the diffusion through holes in the matrix or on the penetration of the compound through a wall or membrane by absorption, solution and diffusion (8). Thus variation in the parameters of the formulations, such as film thickness, particle size, solvent, pore dimensions, etc., alters the release rate. The design of the formulation must therefore take into account the effect of each variable on the emission rate in order to develop a system that is effective during the appropriate cycle of the target insect. 

In this paper, I will describe results obtained in the continuation of this work with the laminate formulations. The laminates consist of an Inner layer that contains the pheromone plus laminating resins and outer layers made of polymeric membranes. The lure diffuses from the inner reservoir through the membrane layers and evaporates from the polymer surface. At the pheromone concentrations that we have evaluated, the release rate generally follows first order kinetics, with the rate proportional to the concentration of lure. The parameters of the polymeric membrane, including thickness and backbone... 

When the dispensers are exposed, the pheromone gradually diffuses out through the outer layers of the laminate and is thereby slowly released to the atmosphere in a manner similar to that of an insect secreting its lure into the air to attract a mate. Since most pheromones are potent, very little pheromone is needed, and the dispensers can frequently contain enough pheromone to last an entire season. Location of the bulk of the pheromone in the inner layer of the plastic protects it from degradation by light, air and weather. This feature can be important because some pheromones are rather unstable (e.g., aldehydes), and they have to be protected until released,... 

Figure 1. The Hereon Disrupt pheromone dispenser. Controlled amounts of active agent move from reservoir layer to surface and subsequent diffusion.

The second system was developed by the Hereon Division of Health Chem Corporation and consists of a laminated plastic chip. Figure 2. The chip is composed of a pheromone saturated polymer reservoir with a semi-permeable plastic membrane on either side. The pheromone is thus released by diffusion from the reservoir through the membrane. The rate is controlled by the membrane composition and thickness(2,). The two systems are applied in a polybutene sticker to facilitate adhesion to the plant surface. 

Several delivery systems have been described in which the primary role of the polymer is to serve as a convenient carrier for the agent rather then serve any specific rate controlling function. Ashare et al, have described a hollow fiber system in whidi the agent is contained within the bore and release is effected by its evaporation and subsequent diffusion through the air above it within the bore. One of its intriguing uses is for release of pheromones, i.e. sex attractants, for control of insects. An alternate concept is release of such agents held within the pore of a suitably constructed open celled polymeric foarn. ... 

Put on safety glasses. Pour a little anunonia in a bowl, place it in one comer of the room, and then walk to the far comer of the room. If you wait a moment or two, the smell of ammonia should reach you because the gas-phase ammonia molecules are very lightweight and diffuse quickly. Insects rely heavily on diffusion. Pheromones, or chemical substances released as odors, are used as a primary method of communication among our more diminutive brethren. The male gypsy moth can detect a burst of a few hundred molecules of a sex attractant from a female gypsy moth located as far as three miles away. Love is a wonderful thing. 

Pheromone was applied in hollow, polyethylene tie-on dispensers placed at regular intervals throughout the vineyard at the rates and timing shown in Table I Initially, each dispenser contained 88 mG of pheromone, a 10 1 mixture of Z-9-DDA and Z-ll-TDA, which slowly diffused through the plastic walls and permeated the vineyard Ten kG samples were harvested from each plot and transported to the laboratory for subsampling, spiking, and frozen storage. 

Most of them are esters. They may also be alcohols, carboxylic acids, lactones, aldehydes, ketones, and hydrocarbons (Silverstein, 1984). Crucial properties of releaser pheromones are their volatility, their stability, and, of course, the degree of specificity possible to build into a relatively small molecule. The molecular weight tends to be between 80 and 300. On the basis of evaporation and diffusion rates, it can be predicted that long-distance sex pheromones would have a molecular weight between 200 and 300. A pheromone may be one chemical, but usually it is a mixture of chemicals, each of which is a component of the pheromone. Mixtures increase the specificity, a property important especially for the sex pheromones. 

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