A comparative study of Hymenopteran Diversity between Kiuic Research Station and Hacienda Tabi in the Yucatan Peninsula of Mexico.

Department of Biology, Millsaps College, Jackson, MS 39210

A survey of families within the order Hymenoptera was performed in two distinct locations in the Yucatan Peninsula of Mexico to determine if a correlation exists between ecological setting and overall family diversity. One site, Kiuic, was representative of a relatively undisturbed section of dry, tropical forest, while the other site, Hacienda Tabi, was characteristic of an agricultural setting. My hypothesis was that a higher diversity of hymenopteran families would be obtained at the relatively undisturbed setting of Kiuic when compared to the disturbed setting of Hacienda Tabi. Using sweep nets, Malaise traps, yellow pan traps and black lights, a total of 26 families of Hymenoptera were collected. The site at Hacienda Tabi yielded 16 families, and the location at Kiuic produced 23 families. The two research sites shared 14 of the same families of Hymenoptera. Two families collected at Hacienda Tabi were not found at Kiuic, and 10 families collected at Kiuic were not found at Hacienda Tabi. Results indicated that a slightly higher family diversity at the site of Kiuic Research Station compared to that at the Hacienda Tabi, but these results could not be confirmed.

Based upon current literature, little is known about diversity of the class Insecta in the Yucatan peninsula of Mexico. Within the class Insecta, the order Hymenoptera is of extreme importance in understanding biodiversity of the region. The diversity of hymenopterans can be an indicator of the condition of other taxa (LaSalle and Gould, 1993; Duelli and Obrist, 1998). For example, one of the major roles of this order of insects is parasitism and predation of other insects. In many of these parasitic groups, the ovipositor has been modified into a stinger which is used as a killing mechanism and/or as an organ of defense (Borror et al., 1989). Therefore, hymenopterans play a vital role in keeping populations of certain insect groups at a healthy level which could lead to greater diversity in the insect community. Also, some families of Hymenoptera are pollinators of flowering plants. In the pollinating groups, the labium and maxillae have been modified into a proboscis which aids in extracting nectar from flowers (Borror et al., 1989). While extracting nectar, these individuals also cross-pollinate the flower which leads to greater diversity and genetic variability within the plant community. With their role as parasites and pollinators, the diversity of hymenopterans is important for the health of the ecosystem.

The order Hymenoptera has many diverse methods of survival, behavior and interaction. Many of the families within this order exhibit eusociality while others are strictly solitary. Some hymenopterans undergo complete metamorphosis and often the larval stage is a grub-like or maggot-like larva. In many hymenopterans, sex is determined by whether or not an egg has been fertilized. Fertilized eggs yield females, while unfertilized eggs yield males (Borror et al., 1989). The different behaviors and survival tactics allow hymenopterans to utilize a wide range of habitats.

MATERIALS AND METHODS

Collections were made over a period of 9 days, using sweep nets, Malaise traps, yellow pan traps, and black lighting. Sweep nets were used to sweep through vegetation along trails. Two different shapes of nets were used in the collecting process. One type had a circular frame with a diameter of approximately sixteen inches, which was used along roadsides and in open areas. The other type of sweep net had a diamond-shaped frame with a width of approximately 22.86 centimeters and was used to sweep through dense vegetation. Specimens were transferred to a killing jar containing either ethanol or ethyl acetate. Most sweep net collecting was carried out between 0800 hours and 1300 hours CDT. In addition, periodic collections were made between 1600 hours and 2000 hours CDT.

Malaise traps were used to collect specimens that may not have been obtainable with sweep nets. A total of five Malaise traps were set up in various flyways and edge habitats throughout the collecting areas. Since there were five Malaise traps, three were set up at Kiuic Research Station and two were used at Hacienda Tabi. The collecting jar was filled with ethanol to allow for a wet collection. Specimens were collected from the Malaise traps once each day.

Two yellow pan traps were placed next to each Malaise trap. Each of the pans was filled with water and dishwashing detergent to act as a surfactant. The surfactant decreased the surface tension of the water, which allowed the insects to sink below the surface so that they would drown and not escape. Traps were checked and specimens collected from them daily.

Ultraviolet traps were also used to collect nocturnal families of Hymenoptera. A white sheet suspended between two trees was illuminated with ultraviolet light. Insects were collected by hand as they landed on the sheet, and transferred to a killing jar containing ethanol. The light was left in place for approximately one hour. Traps were set up one night at Kiuic Research Station for approximately sixty minutes and one night at Hacienda Tabi for the same interval of time.

Collections were processed in the field laboratory set up at Hacienda Tabi. Specimens were sorted into jars labeled with the date, time and place they were collected. The insects of a particular sample were pinned on a pinning block and identified to the family level using the dichotomous keys by Borror et al. (1989), Goulet and Houber (1993), and Rommoser and Stoffolano (1998). Specimens were catalogued and stored in pinning boxes containing para-dichlorobenzene to discourage infestation.

RESULTS

The results are indicated below in Table 1. A total of 26 families of hymenopterans were collected between the two different collection sites. The site at Hacienda Tabi yielded 16 families, while collections from Kiuic contained 23 families. The two research sites shared 14 of the same families of Hymenoptera. Two families collected at Hacienda Tabi were not found at Kiuic, and 10 families collected at Kiuic were not found at Hacienda Tabi.

DISCUSSION

As indicated in Table 1 fourteen families were common to both collection sites in the study. These families include Ichneumonidae, Ormyridae, Eucollidae, Bethyliidae, Dryinidae, Sphecidae, Halictidae, Apidae, Tiphiidae, Mutillidae, Bradynobaenidae, Pompilidae, Vespidae and Formicidae. The extensive overlap of families collected at the two locations could be a reflection of the broad habitat requirements of those families.

Ten families of the order Hymenoptera were collected at the relatively undisturbed dry tropical forest of Kiuic Research Station, but not at the more disturbed area of Hacienda Tabi: Evaniidae, Braconidae, Torymidae, Eucharitidae, Chalcididae, Diapriidae, Scelionidae, Colletidae, Andrenidae and Sapygidae. The presence of some families such as Torymidae, Diapriidae and Sapygidae at only the Kiuic collection site may be due to the relatively specific requirements of these families for survival. Members of the family Torymidae feed upon gall insects, mantid eggs and certain seeds, while the family Diapriidae are reliant upon certain groups of Dipterans, especially those that feed upon fungi. The family Sapygidae is limited to the family Megachilidae, the leaf-cutting bees, and wasps for a food source (Borror et al., 1989). In all three families, the specificity of food sources required for survival might be the reason why they appear in the biologically diverse region of Kiuic rather than the Hacienda Tabi. As for the other seven families--Evaniidae, Colletidae, Braconidae, Eucharitidae, Chalcididae, Scelionidae and Andrenidae--the requirements for survival are broader. Therefore, I would have expected to find them at Hacienda Tabi as well as Kiuic, but did not.

Two families of Hymenoptera were obtained at Hacienda Tabi that were not found at Kiuic Research Station: Xiphydriidae and Scoliidae. Specimens of the family Xiphydriidae were harvested via malaise traps, while those of the family Scoliidae were collected in sweep nets. A possible reason that the family Xiphydriidae was represented at Tabi and not at Kiuic is the abundance of deciduous trees associated with the surrounding fruit farms, which would provide a large amount of decaying wood necessary for the larvae of this family. The collection of a member of the family Scollidae at Tabi could be due to the large numbers of scarab beetles associated with human habitation, which would provide food for the Scollidae (Borror et al., 1989). Since both decaying wood and scarab beetles are also found at Kiuic, these families may well be found there when collecting is extended.

The work reported here is a preliminary attempt to catalog the diversity of hymenoptera at the two locations. Future studies should be designed to ensure that collecting effort is equivalent at each site. Also, further taxonomic categorization may be necessary to make definitive conclusions in comparing the hymenoptera diversity of the two areas. Nevertheless, a great deal of research in the field of entomology is waiting to be explored on the Kiuic Research Station in the Yucatan Peninsula of Mexico.

Table 1. A comparison of hymenopteran families collected between Kiuic Research Station and Hacienda Tabi.

Families of          Collected at    Collected at    Number of
Hymenoptera            Hacienda         Kiuic        Specimens
Collected                Tabi          Research      Collected
                                       Station
Scoliidae               [check]                          1
Xiphydriidae            [check]                          1
Formicidae              [check]        [check]           30
Vespidae                [check]        [check]           20
Apidae                  [check]        [check]           27
Ichneumonidae           [check]        [check]           31
Sphecidae               [check]        [check]           24
Dryinidae               [check]        [check]           4
Pompilidae              [check]        [check]           4
Bradynobaenidae         [check]        [check]           3
Tiphiidae               [check]        [check]           6
Halictidae              [check]        [check]           9
Eucollidae              [check]        [check]           4
Bethyliidae             [check]        [check]           3
Ormyridae               [check]        [check]           2
Mutillidae              [check]        [check]           6
Braconidae                             [check]           7
Colletidae                             [check]           2
Scelionidae                            [check]           2
Chalcididae                            [check]           2
Torymidae                              [check]           1
Diapriidae                             [check]           1
Eucharitidae                           [check]           3
Evaniidae                              [check]           1
Andrenidae                             [check]           1
Sapygidae                              [check]           1

ACKNOWLEDGMENTS

I would like to thank Dr. James P. McKeown and Dr. Sarah Armstrong for their support and direction, the Universidad Autonoma de Yucatan, my colleagues, and Sigma Xi research foundation for funding.

(1) Author for correspondence: 1478 Clairmont Rd., Decatur, GA 30033

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, New York. 875 pp.

Duelli, P., and M.K. Obrist. 1998. In search of the best correlates for local organismal biodiversity in cultivated areas. Biodiversity and Conservation 7:97-309.

Goulet, H., and J.T. Huber. 1993. Hymenoptera of the world: An identification guide to families. Agriculture Canada. Research Branch. 668 pp.

LaSalle, J., and I.D. Gould. 1993. Hymenoptera: their diversity and their impact on diversity of other organisms. Pages 1-26 in J. Lasalle and I.D. Gauld, editors. Hymenoptera and Biodiversity. CAB International, Washington, D.C.

Rommoser, W.S., and J.G. Stoffolano Jr. 1998. The science of entomology, 4th ed. WCB/McGraw Hill, Boston. 605 pp.