Volume 17, Number 2 .... May 1995

Monitoring Anghrenus verbasci (L.) in museum collections using a sex pheromone lure

1. Introduction

The monitoring of insect populations has long been recognized as an essential component of any successful pest control program (1). To this end visual inspections have often been supplemented by the introduction of various insect traps including sticky traps, light traps, pitfall traps and pheromone traps. Insect traps baited with pheromones are a relatively recent development and their introduction has added another dimension to physical trapping techniques. Though developed primarily for use in agriculture and the stored product industry, pheromone traps have great potential for the detection of many museum pests.

Pheromones are chemical compounds secreted by insects to communicate with other members of its species (2,3). Pheromones act as chemical signals which cue mating, aggregation, feeding and mass attack. To date, attention has focused on the study of sex and aggregation pheromones and, as a result, their commercial application has been the most exploited. In general, sex pheromones are produced by the female of the species to attract males whereas aggregation pheromones are produced by the male to attract both sexes.

Commercial pheromone traps incorporate lures containing synthetic pheromones. These are dispersed using a variety of controlled release mechanisms which vary in design and construction depending upon the behavioral response patterns of different insect species. In general, pheromone traps are designed to maximize the attraction of the pheromone lure while optimizing access to crawling or flying insects.

Pheromone traps are a particularly valuable tool for monitoring insect activity and their use possesses a number of advantages over traditional physical trapping techniques. In particular, they can detect the presence of an infestation at a very early stage unlike traditional trapping techniques. Though the proper placement of pheromone traps is essential in order to maximize their efficiency, this is not as critical as in the case of sticky traps and pitfall traps which will only capture pests when they are placed near harborages or feeding sites. The effectiveness of insect traps containing food attractants are also limited by the amount of competing feeding attractants in the environment.

In addition to locating the source of an infestation, pheromone traps can be used to monitor its spread as well as the effectiveness of subsequent pest control measures. In this respect, pheromone traps may also be used to improve the timing of insecticidal treatments thus reducing the amount of insecticide used. If population levels are low, pheromone traps may also be used for mass trapping of insect pests. While complete control is unlikely under these conditions, the insect population may be reduced to a level which is tolerable and which would not require the use of toxic insecticides.

To date, pheromone traps have been little utilized for monitoring insect pests in museums (4,5). In the following study sticky traps containing a newly developed sex pheromone lure for Anthrenus verbasci were used to monitor the presence of this common museum pest in the collection storage areas of the Essig Memorial Museum of Entomology on the campus of the University of California at Berkeley. According to staff, infestations of Anthrenus verbasci are endemic to the museum and over the years have done extensive damage to the entomology collections.

Natural population levels of Anthrenus verbasci in the grounds outside the museum were also monitored in order to determine when this species is active and if observed fluctuations in population within the collection storage areas correspond to seasonal changes in population growth. The results of these experimental trials are presented.

2. Anthrenus verbasci (6)

Anthrenus verbasci is a common museum pest (7). Damage is confined to the larval stage which feeds on a range of plant and animal matter including skins, feathers, wool and furs. Natural history specimens and, in particular, insect collections are especially vulnerable to attack.

Though it is a cosmopolitan pest, Anthrenus verbasci may well be native to California. In his study of the natural habitat of this species, Linsley states (8):

"In the field, as in the laboratory, this species has but one generation a year. The winter is passed in the larval stages, and when temperatures are favorable, feeding continues during this period. In early spring (about the middle of March in central California) the larvae pupate and transform to adults. In the field, the pupal period usually requires between two and three weeks, although as little as nine days may be involved under laboratory conditions. After transformation, the adults remain in the larval skin for a day or two and then emerge, seeking flowers for mating and feeding".

According to Linsley, Anthrenus verbasci occurs naturally in wasp and bird nests which are ideal harborages and breeding sites given the wealth of proteinaceous material upon which to feed (8). These natural reservoirs are often the source of serious building infestations. Flowering plants and gardens adjacent to buildings are also a source of infestation given that adult beetles, having mated and fed, may enter through open windows or on cut flowers.

3. Materials and Methodology: Pheromone lure and trap

Both the pheromone lure and trap used in this study were supplied by the Fuji Flavor Company of Japan. The lure consists of a single tablet impregnated with a mixture of (Z)-5 and (E)-5-undecenoic acid, the natural sex pheromone of the female adult varied carpet beetle. Each tablet is covered with a permeable plastic membrane which controls the release of the pheromone.

The trap consists of a single sheet of cardboard approximately 30cm long and 12cm wide which can be folded back upon itself to form a triangle with open sides. The inner surface of the trap is coated with an adhesive to immobilize beetles drawn to the lure which is placed inside the trap.

The presence of 5-undecenoic acid in the lure was confirmed by GC-MS (9). The pheromone content of a single lure was determined by extraction, followed by capillary GLC analysis using an internal standard. A total load of 0.752mg was estimated (10). A four day aeration study using GLC analysis yielded a diffusion rate of approximately 1752 nanograms of pheromone per day.

4. Methodology

Traps containing the sex pheromone lure for Anthrenus verbasci were placed in a grid pattern in a room (125m2) on the top floor of the Essig Memorial Museum of Entomology, Test room #1. A total of 10 pheromone baited traps and 10 unbaited traps were suspended approximately 1 meter off the ground using the walls and cabinets as supports.

The traps were monitored for a period of two years (1993/1994) during which time their contents were examined once a week. The species, sex and number of all insects present were recorded.

Both the lures and sticky traps were replaced once every 4 weeks as recommended by the manufacturer.

In 1994 the trapping studies were expanded to include a second nearby room (20m2), where many live, larvae and adult Anthrenus verbasci had been observed the previous year (Test room #2 houses the study collections for the entomology students). Two pheromone baited traps and 2 unbaited traps were placed in opposite corners of the room approximately 2 meters off the ground.

Natural population levels of Anthrenus verbasci were monitored by suspending delta traps, with and without the sex pheromone lure, from various shrubs and trees (Pittosporum tobira and Rhapiolepis umbellata) in the grounds immediate outside Wellman Hall. A total of 6 pheromone baited traps and 6 unbaited traps were used.

5. Results and discussion

Over the entire two year monitoring period no beetles were caught in any of the traps placed in Test room #1. Evidence of old insect infestations (cast skins) was found in a number of boxes and cabinets but no live insects were identified other than Attagenous megatoma. These results do not suggest the presence of any active insect infestation in room #1 which may be attributed to Anthrenus verbasci.

The results of the trapping studies in Test room #2 are given in Figure 1. A total of 11 male beetles, identified as Anthrenus verbasci, were caught in the traps baited with the sex pheromone lure. No beetles were caught in the unbaited traps. All trap catches occurred during the first week of April, 1994, coinciding with their occurrence in the traps placed outdoors (see below). Not surprisingly, most of the beetles were caught in the pheromone baited trap nearest the window (north facing). It is well known that adult insects of this species are attracted to light and the latter may well have enhanced the trapping efficiency of the pheromone baited trap.

FIGURE 1. Total number of adult A. verbasci trapped in Test room #2 in 1994.

The source of the infestation was traced to several wasp nests suspended from the ceiling approximately two meters distance from the traps. When subsequently examined by the author, the nests were found to contain a considerable amount of frass and cast skins as well as live Anthrenus verbasci larvae. As previously mentioned, wasp nests are a natural reservoir for Anthrenus verbasci and their introduction into the collection storage areas a number of years earlier is probably responsible for the observed infestation.

The results of the trapping studies undertaken on the grounds outside Wellman Hall are given in Figures 2 and 3 for the years 1993 and 1994, respectively. Though some beetles were caught in late March, the majority were trapped during the months of April, May and June. All beetles were identified as male, Anthrenus verbasci. No beetles were caught in the unbaited traps. These results attest to the attractiveness of the pheromone lure and are consistent with the ecology and behavior of Anthrenus verbasci (8). As previously mentioned, in early spring young adults will seek flowers for mating as well as feeding. Flowering plants probably play an important role in the mating process by drawing male and female beetles sufficently close to allow visual and/or pheromonal communication. Close proximity would be essential given that the sex pheromone for Anthrenus verbasci is a long chain fatty acid and, hence, not very volatile.

FIGURE 2. Total number of adult A. verbasci trapped outdoors in 1993.

6. Conclusion

The data derived from this study is somewhat inconclusive given the relatively low number of trap catches, particularly indoors. This may simply reflect a low population density of Anthrenus verbasci or, alternatively, poor trap efficiency. Controlled release studies are needed to establish trap efficiency under both laboratory and field conditions. Without this information, it is not possible to monitor population levels of Anthrenus verbasci with any degree of confidence.

However, these studies do suggest that this particular pheromone trap can be used to detect the presence of Anthrenus verbasci though timing and trap placement are critical given that adult males of this species are short lived and emerge over a well defined period of time during the year both indoors and outdoors.

The greater number of outdoor catches does raise the interesting possibility of using these pheromone lures to mass trap Anthrenus verbasci on the grounds immediately outside a building as a means of minimizing the number of insects entering the structure through open windows or doors.

REFERENCES

1. Pinniger, D., Insect Pests in Museums, Institute of Archaeology Publications, London (1989).

2. Beroze, M., and Kydonieus, A.F., Pheromones and their use, in Insect Suppression with Controlled Release Pheromone Systems, V. 1, A.F. Kydonieus and M. Beroze, ed., CRC Press, Boca Raton (1982) 3-12.

3. Burkholder, W.E., and Ma, M., 'Pheromones for monitoring and control of stored product insects', Annual Review of Entomology (1985) 257-272.

4. Gilberg, Mark, 'Pheromone traps for monitoring insect pests in museums', IIC-CG Newsletter 17 (1992) 9-11.

5. Gilberg, M., and Roach, A., 'The use of a commercial pheromone trap for monitoring Lasioderma serricorne (F.) infestations in museum collections', Studies in Conservation 36 (1991) 243.

6. Parker, T.A., 'Hide and carpet beetles', in Handbook of Pest Control, ed. A. Mallis, Franzak and Foster Co., Cleveland, 7th ed. (1990) 377-413.

7. Story, K., Approaches to Pest Management in Museums, Smithsonian Institution, Suitland, Maryland, (1985).

8. Linsley, E.G., 'Natural sources, habitats, and reservoirs of insects associated with stored food products', Hilgardia 16 (1946) 187-214.

9. Analysis performed by Environmental Deterioration Research Division, Canadian Conservation Institute, Ottawa, Ontario, March 1994.

10. Analysis performed by Stored-Product Insects Research Unit, Agriculture Research Service, U. of Wisconsin, Madison, WI, August 1994.

ACKNOWLEDGEMENTS

The author wishes to thank the Getty Conservation Institute for providing funding in support of this project and to Art Slater (Pest Management, U.C. Berkeley) for his generous assistance in undertaking these trials.