William G. Eberhard

The Predatory Behavior of Two Wasps,Agenoideus Humilis (Pompilidae) and Sceliphron Caementarium (Sphecidae),on the ORB Weaving Spider Araneus Cornutus (Araneidae)

The nesting habits of many wasps have been studied, but much less is known of how they locate and capture their prey. Many wasps in the families Pompilidae and Sphecidae prey on orb weaving spiders, and knowledge of their predatory behavior is crucial to an understanding of the biology of orb weavers. This paper describes the hunting behavior of two species of wasp, Agenoideus humilis (Pompilidae) and the mud dauber Sceliphron caementarium (Sphecidae) which were observed preying on the orb weaver Araneus

Chrosiothes Tonala (Araneae, Theridiidae): A Web-Building Spider Specializing on Termites

A variety of spiders in web-building families or descended from web-building ancestors are specialist predators on certain types of prey. Some are spider specialists, such as the theridiids Argyrodes (Clyne 1979, Eberhard 1979, Shinkai and Shinkai 198 1, Whitehouse 1987), metids (Bristowe 1958, Jackson and Whitehouse 1986), and the araneid Chorizopes (Eberhard 1983). Others are ant specialists, such as deinopids (Robinson and Robinson 1971, Coddington and Sobrevilla 1987) and the theridiid Euryopis (Carico 1978), and perhaps also the theridiids Steatoda (Holldobler 1970), Dipoena (Jones 1983, Shinkai 1984), and Saccodomus (McKeown 1953). Species in several araneinine genera are apparently moth specialists (McKeown 1953, Robinson and Robinson 1975, Eberhard 1980, Stowe 1986). This note documents an additional case of prey specialization by a web-builder that involves an especially unlikely combination of spider and prey: a tiny species in the family Theridiidae, Chrosiothes tonala Levi, and the wingless worker and soldier castes of the termite Tenuirostritermes briciae (Snyder) which builds underground nests (Nutting 1970).

Fighting Behavior of Male Golofa Porteri Beetles (Scarabeidae:Dynastinae)

Large males of Golofa porteri possess several striking secondary sexual characteristics: the head has a long, curving horn with serrations along its edges; the prothorax has an even longer, thinner, nearly vertical horn which is smooth and covered on its anterior surface with a thick mat of golden hairs; and the front legs, especially the robust tibiae and tarsi, are monstrously elongate, with the last tarsomeres sporting thick growths of golden hair on their ventral surfaces. Howden and Campbell (1974) observed two struggles between males in nature at apparent feeding sites on long thin stalks of a bamboo-like plant. Wille (1943) also noted G. aegeon (especially males) on sugar cane stalks. This study is a follow-up of these observations to determine the functions of the males’ bizarre secondary sexual structures.

The Process of Intromission in the Mediterranean Fruit Fly, Ceratitis capitata (Diptera: Tephritidiae)

The distiphallus of the male of Ceratitis capitata is folded back 180° onto the basiphallus during the early stages of intromission, and is then unfolded within the female. Repeated folding and unfolding may occur within the female. Two membranous sacs on the distiphallus are capable of rhythmic cycles of inflation and deflation. Inflations of the sac near the base of the distiphallus probably help propel the aedeagus deeper into the female, along with periodic stiffening of the basiphallus; inflation of the larger, distal sac may drive the genital rod (which does not transfer sperm) into the ventral receptacle.

The “sawtoothed” orb web of Eustala sp. (Araneae, Araneidae), with a discussion of ontogenetic changes in spiders' web-building behavior

Convergence has been common in the evolution of orb-weaving spiders’ webs, and structures such as stabilimenta, reduced orbs, spring lines, meshes at the side of the orb, and asymmetrically extended ladder webs have arisen independently in a number of different groups. This paper describes brief observations of Eustala sp. that demonstrate still another apparent convergence that is perhaps more surprising than some of the others since the adaptive advantage of the convergent design is at first glance unclear. Ontogenetic changes in web design are also documented for Eustala sp.; younger individuals make more generalized or less derived webs than those of adults. Data on ontogenetic changes in the web forms of other spider species are summarized, and it is shown that this is a common ontogenetic pattern in spiders. The possible significance of this evolutionary pattern is discussed. Observations were made in February 1984 in Parque Nacional Corcovado on the Osa Peninsula of Costa Rica in second growth along a small stream near the Sirena station. Webs of six large nymphs and adult females and of two very young nymphs were observed. The construction of three of these webs was observed between 7 and I1 PM. Spiders were kindly identified by H. W. Levi. They apparently represent an undescribed species; voucher specimens (#2345, SAI-127b, and SAE-106) have been deposited in the Museum of Comparative Zoology in Cambridge, Mass. 02138, U.S.A.

Ritual Jousting by Horned Parisoschoenus expositus Weevils (Coleoptera, Curculionidae, Baridinae)

Males of the weevil Parisoschoenus expositus use their prothoracic horns as weapons in stylized battles with other males over females that are drilling oviposition holes in palm leaves. The unusual sheath-like structures that penetrate deep into the male prothorax function to receive the horns of opponents during battles. Horn size is dimorphic with respect to body size, and small and large males also differ behaviorally. Small males that have mated with a drilling female are sometimes able to impede a large males access to the female until after she has oviposited, but they are not able to take over females from larger nmales.

The Natural History of the Fungus Gnats Leptomorphus Bifasciatus (Say) and L. Subcaeruleus (Coquillett) (Diptera: Mycetophilidae)

Although there are many species of Mycetophilidae (or Fungivoridae) and some that are quite common, little is known about the natural history of most species. The literature on the genus Leptornorphus is typically scanty there are no descriptions of any activities of adults, and only brief descriptions of the general habitat and activities of eggs, larvae, and pupae of one species, L. walkeri (Edwards 1925, Brocher I93I, Madwar 937). This report, which includes observations on all life stages of Leptomorphus bifasciatus and L. subcaeruleus, is the first study of the natural history of these species.

Pupation in Mycetophilid Flies: a Correction

In a previous paper (Eberhard 1970) I made several claims regarding two species of the mycetophilid fly genus Leptomorphus: 1) the larval cuticle is not shed prior to pupation; 2) the last two and one half segments of the larva are discarded at pupation; and 3) the larval head capsule is engulfed by the pupa during pupation (Eberhard 1970). Recent, more detailed observations of Leptomorphus sp. have shown that points 1 and 3 are probably wrong, and this note is an attempt to present a more accurate account of pupation. Observations were made during Sept. 1984 near San Jose, Costa Rica on larvae living on the undersurface of a fungus-covered board, where they inhabited silken sheets with slime trails similar to those of L. bifasciatus and L. subcaeruleus (Eberhard 1970). One observation of the process of pupation was made under a dissecting microscope. This larva hung on an approximately horizontal pupal line fastened at either end to a glass slide, and was observed from above (i.e. from the larvas ventral surface); occasionally I tilted the slide so as to check the larva in lateral view. Species identification in the genus Leptomorphus is not presently possible (R. Gagnk, pers. comm.); voucher specimens of adults reared from the larvae observed are deposited in the U .S. National Museum.