History of Pheromones

by David K. Mueller, BCE

In the late 1950s, scientists clipped thousands of genitalia from the silkworm moth, Bombyx mori, in order to extract its pheromone. Since this time more than 1,000 pheromones have been identified by scientists worldwide. Many more will surely follow in the years to come.

Pheromones are chemical messengers used by insects to communicate and are similar to the hormones inside the human body. Originally they were called ecto-hormones or messengers outside the body. In 1959, two German scientists suggested in an article in Nature that the name pheromone be coined. This word comes from two Greek words: horman, to excite, and pherein, to carry.

Nearly every person has stopped at one time to observe ants as they follow each other along an organized trail. Upon finding a food source, ants lay down a trail pheromone using their abdomen. Fellow worker ants are lured by the pheromone to the trail that leads to the food source. Ants use other pheromones to their advantage, including the defense pheromone released by fire ants to come to the defense of their colony.

Hedges and Lacey (1996) state in the PCT Field Guide for the Management of Structure-Infesting Beetles: "Entomologists and chemists work together to try and identify the specific pheromones used by our most destructive pests and then figure out how to use their discoveries against the insect to its detriment."

Pheromone-baited traps by themselves do not constitute integrated pest management (IPM). IPM is a philosophy, not a particular product or strategy. Too many people working in pest control and sanitation today believe that they are performing IPM when they use pheromones, IGRs, and less toxic practices. IPM programs must begin with the target insect first and then be developed around creating an environment in which the pest cannot survive, forcing it to either leave or die. Pheromone-baited traps are a tool that is used to detect the presence of particular insects and to help pinpoint areas of activity.

The Original Sticky Pheromone Trap

Nature has done its own analysis of pheromones. Semi-chemicals are present in nature in very primitive, as well as magnificently sophisticated, displays of efficient use of energy and resources. The Bolas spider, Mastophora spp., was reported to attract the male pyralid moths to its unique capturing device with the use of two different self-made pheromones.

Long before entomologists learned to use pheromones the Bolas spider was patiently attracting its next meal with a moth sex attractant pheromone. Bolas spiders attract certain male moths by aggressive chemical mimicry of those moth species’ sex pheromones. This unique hunting spider is commonly found throughout the United States. They spin a line, weight it with a sticky drop of liquid silk (the bolas), and hurl it at their prey, much as the gauche throws his bolas or the angler casts his line says arachnologist.

  • Willis Gertsch (1947).

  • USING PHEROMONE TRAPS

  • Effective use of pheromone-baited traps requires much more than simply placing the traps.

Placement of Pheromone Traps

Pheromone traps are effective tools for monitoring stored product pests, especially moths, such as Indian meal moths and Mediterranean flour moths. Pheromone traps are often used in food warehouses and food processing facilities.

In such sites, place traps in a grid pattern to pinpoint new infestations. If vertical support beams are present, use them to set a grid pattern. Many warehouses have 40-foot by 60-foot bays established by their vertical supports. Some warehouses do not have vertical support beams, and in these cases, the pallet racking or other means can be used to secure a natural grid for a pheromone trapping program.

Many warehouses have fire extinguishers set evenly around the warehouse that will offer a site for a trap. The size of the grid will vary with the type of trap and the facility, but as a general rule, intervals of about every 50 feet produce good results. If an area seems to have an infestation, more traps should be placed around that location to help zero-in on the infested goods.

Traps should also be placed near potential insect harborages, such as corners, beams, and entry and exit points (e.g., corridors). As a rule, traps for flying insects should be placed at a height of about 6 feet. Avoid placing traps near exterior doors and windows, as this could lure insects from outdoors.

"It is important to be flexible when starting a pheromone trapping program for the first time. The inspector must be prepared to move traps, add traps, and remove traps in a building being monitored."

The use of pheromone traps should not be limited to large food ware-houses and food processing plants. They can be useful as well in smaller facilities such as restaurants, grocery stores, health food stores, pet stores, and even private homes. A few well-placed traps can be an early warning system to detect newly arrived infested goods and prevent wider infestations.

Outdoor Trapping with Pheromone Traps

Like outdoor rodent control trapping, outdoor pheromone trapping can be very important in a complete pest management program. Insects are naturally present outdoors feeding on grass seed, dead animals, bird nests, pollen, and spilled grain.

The purpose of an outdoor trapping program is four fold: (1) to mass trap as many target pests as possible so that they do not enter the building; (2) to intercept the target pest from truck doors and other openings around the building; and (3) to pull insects from in-side the building out into the traps; (4) an awareness tool to show why doors should be closed.

A careful study of trap catches may shed light on possible infestation sources. For example, it is possible to look at the hairs (setae) on the back of a beetle and deter-mine the food source in which they were last crawling. Such a food source might be flour, food ingredients, or outdoor pollen.

A whitish Trogoderma beetle in an outdoor trap could mean that it came from the inside of the building. Truck doors are often left open during warm weather and serve as a possible entry point for pests. Placement of a horseshoe-shaped line of traps outside about 75 feet away from doorways can intercept pests trying to enter the building.

It is useful for the pest management professional to place a pheromone trap inside/outside his/ her home or office. A quick glance into the trap each day will provide a source of valuable information— (i.e. when the next generation of target pests has emerged in that geographic region).

The Practical Use of Pheromones

Using Pheromone Traps in a Warehouse

Determination of the presence, or absence, of potentially harmful pest insects is needed wherever stored commodities are held for extended periods of time. Pheromone traps are excellent tools for this purpose.

All pheromone traps were not created equal. Traps for moths may perform differently than beetle traps. Pest management professionals cannot treat all stored-product pests the same when it comes to recommending an effective trapping program. Long-lived insect adults (e.g., flour beetles) tend to be less attracted to pheromone traps than short-lived insect adults.

A flour beetle adult that lives for 12 to 18 months does not react as dramatically to a pheromone lure as an Indian meal moth adult that may only live for one or two weeks. Beetles tend to use aggregation pheromones where as moths use sex-attractants. The Pantry Patrol corner trap and the new PC Traps are good tools for stored product beetles.

Knowing the Pest

Knowing the pest is half the battle in controlling it when establishing and managing a grain, bulk commodity, or bagged product pest management program. This fact holds true when interpreting the results and data from a pheromone monitoring program.

For example: Many adult male beetles emerges from the pupae stage five to seven days before the female. When males are captured in pheromone traps, there will be a 5-7day period to find the infestation and implement control measures before the reproductive adult females emerge looking for a mate.

After predicting the first generation of a population in a given year, a prediction of when the second generation is going to emerge can be made by studying the pest’s biology and examining trap capture records from the previous year. For example, Indian-meal moths in the Midwest have appeared in the following cycle: 1st generation appears near May 7, the 2nd generation around June 21, the 3rd generation about July 27, and the 4th generation by September 7. Some parts of the United States will have six Indian meal moth generations per year. At 200-400 eggs per female, an extra generation can mean the difference in controlling or preventing a serious infestation in the fall.

Trap Maintenance

It is important to change pheromone lures on a periodic basis. The length of time specific lures last can range from 4 weeks to 1 year depending on the manufacturer, the sensitivity of the pheromone, and the type package that the lure is stored in. A good rule of thumb for pheromone lure effectiveness is 8 weeks indoors and 4 weeks outdoors. The ideal lure will release a consistent amount of pheromone during the effective duration giving equal.

The date when the trap was placed in service should be noted on the trap it with a “magic marker” type pen. Other record keeping information should not be written directly on the traps as such a practice will only allow unauthorized individuals access to the results of the trapping program. Trap catch information should be maintained on a trap log or computer software each week.

Many lures normally have some pheromone left in them after eight weeks. The old lure can be left in the trap and a new lure can be placed next to the old lure. Discarded lures should be placed into a sealed plastic bag and discarded in an outdoor trash receptacle.

The pheromone trap itself should be discarded when it has captured so many insects that it has lost its ability to hold the target pest. Traps also should be discarded if they begin to have a poor appearance from dirt, scales from moth wings, or from physical damage. Fresh looking traps offer an appearance that a pest management program is well maintained.

Each week, freshly captured insects should be removed from the trap, as this helps in accurately counting newly captured insects the following week. Another reason to remove the insects from the trap each week and replace the traps periodically is that regulatory and quality control inspectors feel more confident about the facility’s control program when they see clean traps compared to those filled with insects.

Common Insect Pests in Grain and Processed Food

Types of Traps

It is important to recognize that no one type of trap is best to use in a pest monitoring program in warehouses. It is important to match the specific trap to the particular conditions in each trapping situation. Some examples include: 1) dusty versus non-dusty area; 2) hot versus cold temperatures; and 3) outdoor versus indoor use 4) crawling vs. flying insects 5. sex-attractant vs. aggregation pheromones.

Too much dust can cause sticky traps to be ineffective. In this situation, alterations to the sticky trap can prevent an excessive buildup of dust, or a pitfall-type trap could be incorporated. Dusty warehouses offer challenges for conventional sticky glue traps. In these extreme conditions, a sticky trap may become useless after several days, or even after several hours. The selection of a trap that can deflect the dust, or a pitfall-type trap that does not include glue as the entrapment mechanism, will need to be implemented.

Outdoor Traps

Trapping for stored-product insects around the outside of a food warehouse can offer several advantages in an overall pest management strategy. The trap selected for outdoor trapping must be able to withstand the weather (e.g., plastic construction, wax coated) and should not be prone to becoming saturated with insects quickly.

By placing pheromone traps on the outer perimeter of a storage facility, potentially destructive insects can be intercepted or lured away from stored food and grain. A feral population of many of the most common stored-product insect pests is present outdoors throughout the United States and Canada . Thus, the outdoor pheromone trapping technique can help the modern pest manager predict the arrival of indoor populations of insects and prevent many from causing an infestation.

Trap Placement

No particular number of traps is right for any particular warehouse to detect the presence or absence of pest insects. The number of traps needed changes according to several factors including:

  • Quality assurance standards by management

  • Agricultural products versus finished goods

  • Pharmaceutical versus raw intermediate products

  • Regulatory pressure

Important questions to ask prior to placement of traps are:

  • What is the goal of the sanitation program? Is the goal zero insect tolerance or lowering customer complaints?

  • Is an attempt being made to reduce the population by mass trapping or to just monitor a pest population?

Here is a situation. The pest management inspector checks each trap weekly and records the results on a trap log. A map made of each trap location can assist in finding the traps and in determining patterns of activity within the warehouse. Each trap in this practical example contains two lures: (1) Plodia complex (Indian meal moth), and (2) Trogoderma complex (Warehouse beetle, T. glabrum, furniture cabinet beetle, Khapra beetle). An optional lure for the Cigarette beetle could be placed in select traps should that beetle also be targeted for monitoring by the pest management professional.

In this situation, it was determined that this warehouse contained few or no detectable target pests in half of the facility, so the traps were moved to the half of the warehouse where insects were found in the pheromone traps. Another approach that may be used instead of moving the traps is to employ more traps in a uniform grid pattern in the suspect areas of the warehouse. After three to seven days, these traps are checked and captures recorded.

At this point, one trap per 50,000 cubic feet is present. If the pest management inspector has more time, he/she can tighten the grid even further to pinpoint the infestation (e.g., one trap per 10,000 cubic feet). The inspector can then start visually searching for signs of an active infestation in the areas where the most insects were captured. Signs of activity might include caste skins of Trogoderma larvae; odor distinctive to certain insects (e.g., flour beetles); webbing on bags, flaps of the bags, or the surface/sidewalls of a grain bin; pupal casings in corrugated cardboard; or actual live insects on finished product.

In one particular warehouse, old code-dated rolled oats were found to be infested with Indianmeal moths, Saw-toothed grain beetles, and Flour beetles. Some nearby dog food also contained large numbers of stored-product insects that could have entered this warehouse from the continuously opened dock door during the summer months. In this example, the cost of the pheromone traps/lures would typically run about $300 to $400 per year. The time needed to count and record seven traps each week would be about 30 minutes per week.

Interpreting Trap Culture

A common misconception in a strategy used to manage grain, bulk commodities, and bagged food products using pheromone traps is that a set numerical threshold exists to trigger either an action or reaction, but no such magic number exists. The inspector must weigh all factors before making a decision. The key factor for interpreting trap catch is to look for increases in numbers of insects from one trapping period to the next (e.g., 1-5-30 ). It is easy to see when an outbreak or new generation emerges. At that point, the appropriate corrective actions (e.g., chemical, non-chemical, sanitation, discarding product) may be devised and implemented.