ABSTRACT

Development of incipient Coptotermes formosanus Shiraki colonies from paired, 1st-form reproductives was studied in field cages.

Eggs occurred in 13 to 109-day-old colonies and in 1 colony 278 days old. No oviposition occurred during the winter of the 1st year of colony development.

Four larval stags occurred during the 1st oviposition period and no 5th stage larvae occurred during the study period (313 days). The appearance of soldiers coincided with development of 3rd stage larvae. Soldiers constituted ca. 10% of colonies containing 48-138 individuals (138 to 313-day-old colonies).

There was only 23-30 cm of gallerying from the nursery area during 313 days of colony development, and once a copularium was formed no further gallerying occurred until some of the young reached the 3rd larval stage. Vertical movement from colder to warmer galleries occurred during winter and spring months.

Soil moisture and temperature in field cages did not differ greatly from that in adjacent uncaged areas.

The Formosan subterranean termite, Coptotermes formosanus Shiraki, is of major economic importance in Asia and islands of the Pacific Ocean and recently was found in southern coastal regions of the United States (Spink 1967). There is little information available on termite colony development in the field and no published reports were found on C. formosanus. However, Oshima (1919), Mori et al. (1964), Bess (1970), and King and Spink (1974) have reported on some aspects of colony development in the laboratory. In the experiment reported herein we studied early development of field colonies.

METHODS

The study area was located on the Louisiana State University (New Orleans) campus near the east shore of Lake Ponchartrain. Soil consisted of fill relatively uniform in texture and composed mostly of sand with some shale particles.

Predominant vegetation during summer and fall was bermuda grass, Cynodon dactylon (L.) Persoon; broom sedge, Andropogon virginicus L.; fennel, Foeniculum vulgare Miller; and Aster sp. In late winter and spring the plot was covered with bedstraw, Galium aparine L. and cranesbill, Geranium carolinianum L.

Field cages consisted of 85-liter galvanized garbage cans with bottoms replaced with 30- mesh aluminum screen⁴ attached by epoxy glue.⁵ Nylon screen (32 mesh) covered the cage tops, and was held in place by the can lid after a hole (30 cm diam) had been cut from its central area. Cage construction permitted rainfall and other atmospheric moisture to enter and drain yet confined the termite colonies and restricted entry of other animals. The cage inside surface was coated with epoxy paint and outside surface with DeRusto compound.⁶ Cages were imbedded in the study area with tops positioned at ground level and filled with soil. The top soil (turf) was replaced in its original position over each cage.

We established C. formosanus colonies in 2.5×2.5×29-cm "Southern pine" stakes (Pinnus spp.) placed below soil level within field cages. Tow holes (1.25 cm diam) were drilled in each stake, 1 longitudinally extending from the top to the point of the stake and the other latterly extending from the center of the stake, 2.5 cm from the top. The stakes were buried beneath soil level for one year, then were removed, split longitudinally, and brushed to remove soil debris and termites (stakes were incidentally infested by Reticulitermes flavipes [Kolar]). The stakes were also infested with wood-inhabiting fungi resulting in some decay, but fungi species was not determined. The grooved center was filled with 1 part pine sawdust and 2 parts water and 2 halves were wired together. A cork was placed in the top hole and the stakes were placed vertically in the field cages with the tops positioned 5-7.5 cm below ground level. Fifty stakes (10/field cage) were prepared for infestation with 1st-form reproductives.

Each stake was infested on May 9, 1970, by removing the cork from the top and introducing one pair (1 male + 1 female) of dealates (adults with wings removed) into the sawdust-filled groove. The cork was replaced and the stake top was recovered with soil. C. formosanus reproductives had been obtained from buildings in New Orleans and held 24 h in the laboratory prior to use in the field. Methods for collecting, immobilizing, sexing, and removing wings of C. formosanus reproductives are presented by King and Spink (1974).

We removed 2 stakes, each containing a live colony, from cages at ca.14-day intervals through 109 days; thereafter, the sampling interval was extended to ca. 30 days. On each sampling date, number of different developmental stages present in each colony was recorded plus notes on colony behavior. Methods for identifying C. formosanus developmental stages from young colonies are given by King and Spink (1974). Position and depth of the nursery (initially, cavity formed by 1st-form reproductives in which copulation [copularium] occurs, but later area in which eggs and young larvae were located) and extent of gallerying in each stake was also recorded. Further, soil temperature and percent moisture within and outside cages was measured at depths of 13, 26, and 39 cm and at the nursery depth. Temperature was obtained with a Wesler® soil thermometer, and soil moisture is expressed on a percentage by dry weight basis (Hanna 1964).

RESULTS

Average number of individuals found in colonies on different sampling dates is presented in Table 1. Average depth of the nursery on different sampling dates is presented in Table 2.

Eight to 11 eggs were found in 13-day-old colonies. Based on consideration of total progeny found, 59-90 eggs were deposited in the 1st 100 days afer pairing in all colonies except one. We found 138 individuals, including 18 eggs, in this colony 278 days after pairing. Most of these eggs contained amorphous white bodies which could be seen through the chorion, and little embryonic development had occurred.

Presence of 1st and 2nd larval stages in 52-day-old colonies indicated that the egg incubation was ca. 30 days. The combined duration of the 1st and 2nd larval stages was ca. 20 days, and presence of 4th stage larvae in 95-day-old colonies indicated the 3rd larval stadium duration was ca. 35 days. These figures represent a maximum rate of development since soil temperatures at the nursery depth were reduced at subsequent sampling dates. Thereafter, 4th- stage larvae accumulated in colonies as no larvae exhibiting 5th-stage characters were found during the study period (313 days). Presolider and soldier stages developed in colonies at ca. the same time as 3rd-stage larvae.

Mean number of individuals occurring in the final 12 colonies sampled was 70.58 with a maximum of 138. The soldier stage constituted 10.7% of these colonies.

The 1st oviposition period apparently ended ca. 100 days after pairing, and no distinct 2nd oviposition period occurred.

Gallerying from the copularium (nursery) was not detected during the 1st 52 days. However, in 67-day-old colonies galleries extending from the copularium occurred, and these coincided with development of 3rd-stage larvae (Fig.1).

Galleries extending 20-22.5 cm down the sawdust groove occurred in 175-day-old colonies. Some of these galleries possessed lateral extensions that had been constructed into solid wood, but no galleries extended into the soil. Galleries extended ca. 23-30 cm from nursery cavities. The copularium was always constructed in the sawdust-filled groove of individual stakes at depths ranging from 12.5 to 15 cm below ground level.

During the 1st 175 days, the nursery was always found in a cavity in the sawdust-filled groove, later nursery cavities were often constructed in solid wood. These nurseries were located at ca. 13.5-18 cm below ground level during the warmer months of the year (May-October); however, during the months of December, January, and February they were located at depths of ca. 22.5, 38, and 28 cm below ground level, respectively. During these months the termites congregated in nurseries and did not occupy galleries. At the termination of this study in March 1971 (313 days after pairing), termites occupied nurseries and galleries nearer the tops of stakes at an average of 8.89 cm below ground level.

Soil moisture within cages was apparently adequate for normal colony development since termite numbers did not fluctuate drastically during periods of high or low soil moisture.

A total of 26 colonies were recovered, 6 from each of 4 cages and 2 from the 5th cage. Of these latter, 1 is included in the 13-day sample and the other in the 69-day sample. The other 8 stakes in this 5th cage were infested with R. flavipes, which were apparently in 1 or more stakes when the study was initiated since galleries entering the cage were not observed. No R. flavipes were found in the 2 stakes containing C. formosanus colonies.

Soil temperature within cages averaged lass than 0.3ºC higher than the soil temperature outside cages, but this difference was significant (P<.05). However, there was no interaction between temperature within cages and (1) sampling dates, (2) sampling depths, and (3) sampling dates + depths sampled.

There was no significant difference (P>.05) between percent soil moisture within and outside cages. However, there was a significant interaction (P<.05) between soil moisture and depths sampled within cages. There was no significant interaction (P>.05) between soil moisture and sampling dates.

DISCUSSION

Techniques used apparently provided favorable conditions for development and survival of incipient C. formosanus colonies. More individuals were recovered per colony, and colony survival was higher, than in other comparable studies conduced in the laboratory. Oshima (1919), Mori et al. (1964), and Bess (1970) stated that only 20-30 eggs were deposited during the 1st oviposition period of C. formosanus, whereas ca. 70 were deposited during the 1st oviposition period in our study. King and Spink (1974) reported ca. 25 and 54 individuals were produced during the 1st oviposition period when laboratory colonies were maintained at 26 and 32ºC , respectively. The fact that termites in our study were not restricted in vertical movement probably allowed them to seek and remain in a favorable environment.

Data on average depth of the nursery at different sampling dates indicates a seasonal response to temperature gradients by C. formosanus colonies. Thus, the nursery area was found in stakes at deeper soil depths in the colder months of winter than in warmer months. Although soil temperature at 7.5 cm was slightly greater than at the nursery depth during January and February, this temperature was maximal since it was taken near midday. Estenther (1969) reported a similar seasonal temperature response for R. flavipes.

Termite activity was sluggish when soil temperatures were below 21ºC. At lower temperatures (ca. 16ºC) they clustered together, and we believe this behavior was an attempt to modify (raise) the temperature. Behavior of this nature has frequently been observed in larger and more mature colonies of C. formosanus when examined in the field during winter months in Louisiana.

The 18 eggs found in one colony in February, 278 days after pairing of reproductives, is difficult to explain on the premise that they were from the 1st oviposition period especially when compared to the shorter duration of the 1st oviposition period of other colonies examined (ca. 100 days). However, we believe that these eggs were deposited during a 1st oviposition period since (1) no eggs were found in other colonies examined in December-March, (2) many of the eggs contained amorphous white bodies and this had previously occurred in eggs held at 21.5ºC (King and Spink 1974), and (3) 5th stage larvae were not found (their occurrence had previously been correlated with the onset of the 2nd oviposition period in other studies by King and Spink 1974). Young larvae, apparently newly hatched from eggs, have been found in Louisiana in mature C. formosanus colonies in the field during the winter. Greaves (1964) reported that large termite colonies can modify (raise) ambient air temperature by as much as 20ºC. Apparently incipient C. formosanus colonies are not able to modify temperatures sufficiently to permit hatching of eggs during the 1st winter after initiation of colonies in Louisiana.

Although a 2nd oviposition period did not occur during this study, in a previous field study (King⁷) a 2nd oviposition was initiated ca. 1 year after pairing. The occurrence of 5th stage larvae coincided with the occurrence of this oviposition period.

Invasion of stakes by other termite species occurred in only 1 of 5 field cages, and in this instance, the termites (R. flavipes) were probably in the stakes when they were buried in the cage. Thus, this type of cage is considered effective for preventing entry of termites, and most other wood infesting arthropods. The presence of R. flavipes in stakes infested with one pair of C. formosanus reproductives apparently prevented establishment of colonies of the latter species.

ACKNOWLEDGEMENT

We express thanks to Dr. M. Yoshimeki for assistance in translating Japanese literature; Dr. J. H. Roberts for assistance in photography; and Dr. G. R. Strother and Mr. Willie Harris for their assistance in collecting termites and preparing field cages. Thanks are also due Louisiana State University at New Orleans for providing space to conduct field research

REFERENCES CITED

Bess, H. A. 1970. Termites of Hawaii and the Oceanic Islands. Pages 449-75 in K. Krishna and F.M. Weesner, eds. Biology of termites. Vol. 2, Academic Press, Inc., New York. 643 pp.

Esenther, G. R. 1969. Termites in Wisconsin. Ann. Entomol. Soc. Am. 62:1274-90.

Greaves, T. 1964. Temperature studies of termite colonies of living trees. Aust. J. Zool. 12:250- 62.

Hanna, W. J. 1964. Methods for chemical analysis of soils. Pages 474-502 in F. E. Bear, ed. Chemistry of the soil, 2nd ed. Reinhold Publ. Corp., New York. 515 pp.

King, E. G., and W. T. S., Spink. 1974. Laboratory studies on the biology of the Formosan subterranean termite with primary emphasis on young colony development. Ann. Entomol. Soc. Am. 67:953-8.

Mori, H., K. Morimoto, L. Shibamoto, H. Kawarmura, S. Amamiya, S. Kamiyama, M. Maeoka, H. Morimoto, L. Mujake, and A. Kaiiuama. 1964. Termite control digest (in Japanese). Termite control Counc. Japan. 142pp.

Oshima, M. 1919. Formosan termites and methods of preventing their damage. Philippine J. Sci. 15: 319-83.

Spink, W.T. 1967. The Formosan subterranean termite in Louisiana. La. State Univ. Circ. 89. 12 pp.

Reprinted from the
ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA

¹ Isoptera: Rhinotermitidae [Return]
² Received for publication July 23, 1974. A portion of a dissertation by the senior author submitted to the Grad. Faculty of Louisiana State Univ., Baton Rouge, in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Entomology. This study was supported in part with USDA Grant 4040-(4000) from the Wood Products Insect Lab., Southern For. Exp. Stn., U.S. For. Serv., Gulfport, Miss.[Return].
³ Res. Entomologist, Bioenviron. Insect Control Res. Lab., Agric. Res. Serv., USDA, Stoneville, MS 38776, and Prof. of Entomology, Entomology Dept., Louisiana State Univ., Baton Rouge 70803, respectively. [Return]
⁴ Ludlow-Saylor Wire Cloth Division. [Return]
⁵ Products Research and Chemical Corp.[Return]
⁶ Master Bronze Powder Co., Inc.[Return]
⁷ King, E. G. 1971. Biology of the Formosan subterranean termite, Coptotermes formosanus Shiraki, with primary emphasis on young colony development. Ph.D. Thesis, Louisiana State Univ. Library, Baton Rouge. 193 pp.[Return]