Zeta is a small neotropical eumenine wasp genus with 4 species that range from Mexico to Argentina and also Trinidad, in the West Indies (Bertoni 1934; Bodkin 1917; Callan 1954; Carpenter 1986b; Carpenter 2002; Carpenter & Garcete-Barrett 2002; Giordani Soika 1975; Martorell & Escalona S. 1939; Rocha 1981a; Rocha 1981b). Zeta argillaceum (L.) (Fig. 1) is probably one of the commonest potter wasps in South America. It is well adapted to urban environments; it is easy to find its distinctive mud nest attached to house walls (Garcete-Barrett, pers. comm.). The nests can be also found in sheltered spots under bridges, electric poles and eaves (Bodkin 1917; Chavez 1985; Rocha 1981b) and can be easily transported on ships, thereby expanding its distribution (Bertoni 1934). The mud cell normally appears uniformly colored, but if not it is often due to subsequent closures of the original emergence hole by inquilines or opportunistic “renter” species (Bertoni 1911).

Recently introduced into the Southern United States (Menke & Stange 1986; Stange 1987), Z. argillaceum appears to be expanding its range. Like mud daubers in the genera Trypoxylon and Sceliphron, Z. argillaceum nests harbor not only its offspring but also numerous other arthropods, including scavengers, parasites and predators, and their nests could be used to teach ecological interactions (Matthews 1997).

Menke & Stange (1986) summarized the nesting biology of Z. argillaceum. They relied heavily on Taffe (1979) who studied the biology of Zeta canaliculatum (=Z. argillaceum) in Trinidad. A similar approach was used to study Z. argillacea (=Z. argillaceum) in Brazil (Rocha & Raw 1982). In many aspects the general biology resembled that of the related Z. abdominale(Drury) (in some cases using its synonym Eumenes colonaSaussure) studied in Jamaica by Freeman & Taffe (1974), Taffe & Ittyieipe (1976), and Taffe (1978, 1979, 1983). Detailed accounts of the inquilines and parasites of Z. argillaceum in Brazil and in Venezuela are given by Bruch (1904), Rocha (1981a, 1981b), Rocha & Raw (1982) and Chávez (1985). Here we present the first biological data for this species from North America, and demonstrate that it is well established in southern Florida.

Materials and Methods

Seventy-three cells of Zeta argillaceum were collected from the roofs of two beach shelters at Hutchinson Boulevard, Martin County, Florida on 28 July 2003. Cells were dissected and contents recorded. Live material was reared under laboratory conditions (25°C, 70% RH) and identified. Voucher specimens were deposited in the entomological collection of the Georgia Museum of Natural History, Athens, Georgia.

Results and Discussion

Nests of Zeta argillaceum consist of rounded, pot-like cells (Fig. 2). Nest clusters contained up to 15 cells. Most contained 4-7 cells, but isolated single cell nests were also found. Most nests in our sample were old and many had been reused, suggesting that the site had been occupied for some time. Taffe (1979) found that Z. argillaceum had 6 generations per year in Trinidad, each requiring about 60 days. In subtropical Florida it is probable that the species can have up to 4-5 generations, leading us to infer that the site had been used for at least a year.

Cells measured 14-18 mm in diameter (Fig. 2) and about 9-13 mm height. Eleven cells were recently made, and contained paralyzed but responsive caterpillars representing two unidentified species of Geometridae. Larvae of this lepidopteran family are reported as common prey of Z. argillaceum elsewhere (Callan 1954; Rocha 1981a). One cell (Fig. 3) contained 19 geometrid caterpillars (15 of one species) and a newly hatched wasp larva. The wasp’s egg (Fig. 4) is suspended in the empty cell.

Many of the remaining cells (52 of 62) were reused by other arthropods. This rate of reuse was higher than previously found in Brazil (42.75%) and Trinidad (42.72%), where the wasp is very common (Rocha 1981b; Taffe 1979). It appears that Z. argillaceum builds a new nest each time, as there are no reports of it re-using old nests. Table 1 lists the arthropods found in the cells of Z. argillaceum. Two other Eumeninae,Pachodynerus nasidens(Latreille) and P. erynnis (Lepeletier) were found reusing Z. argillaceum cells. Pachodynerus nasidens, the most widespread species in the genus and distributed from the U.S. to Argentina, but not in Chile, and also in the Antilles (Carpenter 1986a; Willink & Roig-Alsina 1998), use the cells by dividing them in two by adding a wall in the middle, so from each Z. argillaceum cell 2 P. nasidens wasps will emerge. These wasps reused 24 Z. argillaceumcells. In Brazil, P. nasidens also are recorded to build two cells inside of reused cells of Z. argillaceum (Rocha 1981a; Rocha 1981b). Pachodynerus erynnis, the only red-marked Pachodynerus in the U.S. (J. M. Carpenter, pers. comm.), and restricted to the southeast (Carpenter 1986a; Willink & Roig-Alsina 1998), use the cells unmodified so that only one individual of this species emerges per Z. argillaceum cell. Apparently only two Z. argillaceum cells in our sample were reused by P. erynnis. However, two other Z. argillaceum cells contained dead and mummified larvae of Noctuidae, which could have been prey of that wasp, as found by Krombein (1967). The sphecid Chalybion californicum (Saussure) also reused Z. argillaceum cells (one wasp found in a cell). Taffe (1979) reported cells of Z. argillaceum being reused in Trinidad by Trypoxylon sp. and Amobia sp. The later was probably a parasite of Trypoxylon. Rocha (1981a, 1981b) found that Trypoxylonsp. and Pachodynerus nasidenswere the most common inquilines in old nests of Z. argillaceum in Brazil.

Some of the mortality factors for Z. argillaceum and the opportunistic wasps were a bee fly (Anthrax sp., Diptera: Bombyliidae), the Australian wowbug (Melittobia australica, Hymenoptera: Eulophidae) and one individual of Macrosiagon sp. (Coleoptera: Rhipiphoridae), a known parasite of Eumeninae (Krombein 1967; Genaro 1996), that was found dead inside one old cell. Melittobia australicawas found parasitising Z. argillaceum in two of the cells, and P. nasidens in 4 reused cells. Mold was consuming the prey caterpillars in one cell. Taffe (1979) also mentions mold attack, cuckoo wasps (Chrysididae), Ichneumonidae and especially Melittobia sp. (=M. australica) as the most important mortality factors in this potter wasp in Trinidad as well as in Z. abdominale in Jamaica. Melittobia australica was also found parasitising different Eumeninae in Venezuela including Z. argillaceum (Chávez 1985; González 1994; González & Terán 1996).

At least two species of scavengers were also found. Ten of the Z. argillaceum cells contained carpet beetles (Anthrenus sp. Coleoptera: Dermestidae), while Psocoptera were found only in 1 old cell. Web remnants and live spiders were present in four old cells, which probably served as shelters (Fig. 5). Many other insects present in Florida are also potential users of Z. argillaceum nests, such as Crematogaster ants, that also have been found using old nest cells (Bodkin 1917).

Clearly the persistence of the mud pots of Z. argillaceumafter the emergence of their original progeny provides a home for a diverse community of opportunists and nest associates. The composition of this community no doubt differs from location to location, but generally includes other cavity-nesting Hymenoptera and their parasites, scavengers and associates. In this small sample we found a community involving some 10 arthropod species. Thus, such nests are potentially useful for teaching ecological concepts as well as helping to maintain biological diversity in relatively urban environments by providing shelter and food to other species of arthropods.