A list of Coleopteran families found in disturbed and undisturbed areas in Yucatan, Mexico.

Department of Biology, Millsaps College, Jackson, MS 39210

Families of the order Coleoptera found in two areas of Yucatan, Mexico were listed in an effort to establish a baseline for coleopteran diversity and to determine if unique families could be found in discrete areas. One area was undisturbed dry, tropical forest, and the other was an agricultural plantation; they were 19.7 km apart in linear distance. Insects were captured via sweep nets, Malaise traps, pit-fall traps, black lighting, and Berlese funnels. Insects were killed in Nalgene vials containing cedar chips and a sufficient amount of ethyl acetate. A total of 189 insects were collected and identified over a two-week period representing 23 different families. Of the families recorded, 15 were common to both areas. Only 2 families were unique to the agricultural area, and 6 families were unique to the undisturbed forest area. Based on the insects collected, there was not a marked difference in the families that were found in each area. The unique families could be a result of a collection bias in each area.

Although much is known about the physiology and functioning of beetles in general, very little taxonomic information is known about beetles in the Yucatan. Literature searches yielded very little information about general beetle populations in Yucatan; the articles primarily dealt with particular species and their interactions with the flora of the area. The species level data are too limited for the scope of this project.

The purpose of this project was to start listing the families of beetles present in the Yucatan in order to establish a baseline list of beetle families in that area. This project can serve as a guide for further research in the Yucatan.

Also, an effort was made to determine if there was any difference between which families could be found in the undisturbed versus disturbed areas used as the collecting sites.

MATERIALS AND METHODS

Specimen Collecting Environment--The two areas selected for collection were both highly vegetated but markedly different. The Helen Moyers Reserve at Kiuic, Yucatan, Mexico has been relatively undisturbed for a few hundred years. The only type of disturbances encountered were the trails around the area. The Hacienda San Juan Bautista at Tabi, Yucatan, Mexico is a highly agricultural area with many mango and orange groves in the immediate area. Also, many remains of buildings from an abandoned sugarcane plantation dotted the collection area. These areas were roughly 19.7 km apart in linear distance.

Insects were collected daily over a two-week period during the early rainy season. The majority of insects were collected during daylight hours and in areas not far from established trails. Only the understory served as the prime place for collecting; no canopy collecting was performed. Collection at Kiuic was done typically from 8:00 AM until 1:00 PM, 5 hours, in order to avoid the heat of the day and the daily rainstorms. After returning to Tabi, collection resumed there from 4:00 PM until 7:00 PM, 3 hours. The remaining time was spent keying out and pinning specimens.

Specimen Gathering--For collecting specimens along trails and among bushes the sweep net was the most efficient tool because it was able to cover a large area in each sweep. Contents collected were sorted quickly after sweeping to prevent specimen loss and were deposited into collecting vials containing ethyl acetate.

For collecting at night, light sources were utilized because of their attractiveness to insects. Aside from using the incandescent lights in open-air passage-ways at the laboratory, a black-light system was used for collecting in the densely vegetated areas. A 15-watt black light powered by a 12-volt DC lawnmower battery was hung behind a white cotton sheet. Insects were attracted to the light and landed on the sheet. Specimens were quickly picked off the sheet by hand and placed in collecting vials.

For more passive collecting, pit fall traps were put in place. Only a limited number of traps were available in the field and had to be placed with much discretion. The traps consisted of 2 empty 310.5-mL soup cans buried level to the ground. Between the 2 cans, a stick or plank served as a barrier to direct the insects to the buried cans. The cans were baited with caterpillar dung, fruit, and frog corpses. Once a day over the period of a week, cans were checked and insects were collected from the traps and placed in the collecting vials.

Leaf-litter sorting was performed with two tools. A sifter made of two 30.48-cm metal rings, 1-cm hardware cloth, and rip-stop nylon sorted leaf materials in the field. In the laboratory, the sifted material was emptied into a collapsible Berlese funnel and allowed to dry. At the base of the funnel, a small plastic bag with 2 mL of ethyl alcohol was used to collect insects as they emerged from the desiccated leaf-litter. To provide desiccation, a 60-watt light bulb was hung over the top of the canvas bag and allowed to burn continuously.

Another passive collection method used a Malaise-trap. Three traps were placed at Kiuic, and two traps were placed at Tabi. Traps were placed in areas of various growth densities ranging from dense forest to almost open field. These locations were chosen in an effort to collect as many different insects from different habitats as possible. These traps were checked every day for a two-week period.

Specimen Killing and Pinning--After insect specimens were caught, they were immediately placed in 30 mL, 60 mL, or 118 mL wide-mouth Nalgene vials. Inside the vials were cedar chips, typically found in rabbit bedding, soaked in ethyl acetate, the killing agent. Potassium cyanide was not used because it causes many insect specimens to become brittle. Nalgene vials were used because they are shatterproof and are not affected by chemical contact.

Wooden pinning blocks and Elefant insect pins were used for mounting. Pins in sizes 0,1, 2, and 4 were used to accommodate the range of specimen sizes. The pinned specimens were placed in thick, hinged cardboard boxes with a layer of Styrofoam in the bottom for holding the pins. Small amounts of para-dichlorobenzene were used to protect the collections from infestation by dermestids and other harmful insects.

Specimen Identification--Insects were identified using a Bausch & Lomb 0.7x-3x dissecting microscope with an incandescent light source. All specimens were identified using the Coleoptera key by Borror et al. (1989). Some specimens were cross-checked using a computer program developed by Lawrence et al. (2000). Measurements necessary for identification were made with a standard metric ruler and metric calipers.

RESULTS

Although this study is qualitative in design, Table 1 shows that a total of 189 insects representing 23 different families was catalogued over a two-week period. Of the families recorded, 15 families were common to both areas. Only 2 families were unique to Tabi, and 6 families were unique to Kiuic.

DISCUSSION

The results (Table 1) indicate that there are a few families that were unique to each collecting area. Although unique families were found, none of them were rare. It is likely that even the most novice of collectors could have found them all if the proper parameters were established. Perhaps the most likely reason for finding unique families in each area lies in a collecting bias. Collecting in each area, although performed every day, was done in the same areas around the Malaise traps and the trails leading to the traps. If the traps were moved and different trails were traveled, there might be a mirror-image trend in the families collected at each site. Perhaps if truly equal time were given to each site, more of the same families would have been collected. With so many biases built into this project, it is difficult to accurately compare the diversity between the two sites.

   Family         Number       Location
                    of        Collected
                 Specimens

Alleculidae          4          Kiuic
Bostrichidae         1           Tabi
Carabidae           10       Kiuic & Tabi
Cerambycidae        12       Kiuic & Tabi
Chrysomelidae       26       Kiuic & Tabi
Cicindelidae        11       Kiuic & Tabi
Corylophidae         2       Kiuic & Tabi
Cucujidae            3           Tabi
Curculionidae        6       Kiuic & Tabi
Dytiscidae           2       Kiuic & Tabi
Elateridae           6       Kiuic & Tabi
Endomychidae         2          Kiuic
Histeridae           1          Kiuic
Hydrophilidae        5       Kiuic & Tabi
Lampyridae           8       Kiuic & Tabi
Lycidae              3          Kiuic
Nitidulidae          2          Kiuic
Passalidae           9       Kiuic & Tabi
Phalacridae          2          Kiuic
Phengodidae          5       Kiuic & Tabi
Scarabaeidae        40       Kiuic & Tabi
Tenebrionidae       17       Kiuic & Tabi
Trogossitidae        5       Kiuic & Tabi

ACKNOWLEDGMENTS

The author would like to thank Millsaps College Biology Department for funding this project through a Research Fellowship in Field Biology and Hugo Delfin and Vickie Martinez, entomologists at the Universidad Autonoma de Yucatan, for their guidance and help while in the field. Also, the author would like to thank Dr Drew Hildebrandt, Director of Research, Cardiothoracic Surgery, University of Mississippi Medical Center, for suggestions for the project, assistance with equipment, and a few good meals.

(*)Author for correspondence: Mississippi Entomological Museum, Box 9775, Mississippi State, MS 39762-9775, [e-mail]

LITERATURE CITED

Borror, D.J., C.A. Triplehorn, and N.F. Johnson. 1989. An introduction to the study of insects. 6th ed. Harcourt College Publishers, Fort Worth. 875 pp.

Lawrence, J.F., A.M. Hastings, M.J. Dallwitz, T.A Paine, and E.J. Zurcher. 2000. Beetles of the world: A key and information system for families and subfamilies: Version 1.0 for Microsoft Windows. CD-ROM. CSIRO Publishers, Canberra, Australia.