Doryphora paykulli ( Stal , 1859)

Windsor, Donald M., Dury, Guillaume J., Frieiro-Costa, Fernando A., Susanne Lanckowsky, & Pasteels, Jacques M., 2013, Subsocial Neotropical Doryphorini (Chrysomelidae, Chrysomelinae): new observations on behavior, host plants and systematics 1, ZooKeys 332, pp. 71-93 : 73-75

Doryphora paykulli ( Stal, 1859)

Remarks.

According to Blackwelder (1982) the range of this large beetle (19.8 ± 1.5 mm, n=6) (Figs 1 a–c) extends from Mexico to Nicaragua. However, specimens collected later (L.D. Gomez near San Vito, Costa Rica; H. Stockwell, Cerro Campana, Panama Prv., 30 V 70 and 18 VII 76; D.M.W., Los Santos Prv., Cerro Canajagua, 25 V 92 and Colon Prv., Cerro Galera, 1 V 02; M. Cuignet, Colon Prv. Sta. Rita Ridge Rd. km 2, 2 XI 02; S. Van Bael, Bocas del Toro Prv., Chiriqui Gde., 17 I 04; M. Membache, 1 VI 92, Colon Prv., Gamboa; S. Lankowski, Panama Prv., Parque Metropolitano, 15 IV 07) indicate the species extends to at least 10 km east of the Panama Canal. These records plus observations of a Doryphora paykulli adult following a tightly arranged group of larvae moving between leaves on their food plant near Chiriquí Grande, Bocas del Toro Province (S. Van Bael, pers. comm.) documents the presence of the species in the Caribbean as well as in the Pacific lowlands of Panama and provides the first unequivocal record of subsocial habits for the species.

Subsequently, individual Doryphora paykulli adults were observed (D.W., S.L.) during late April and early May of 2005 moving slowly and feeding among low vegetation. Pairs of individuals were observed interacting aggressively on the small leaf fragments remaining on the host plant, Prestonia seemannii Miers ( Apocynaceae ) under late dry season conditions along trails in the Parque Metropolitano (elevation 30 m, 8°59.24'N, 79°32.797'W), Panama City. Whether these were contests over resources or precopulatory courtship is unclear, however, analysis of video taken of one of these interactions shows the use of the mesosternal horn in dislodging a competitor, much as described by Eberhard (1981) for the closely related beetle, Doryphora sp. near punctatissima. Adult females were discovered during mid-May of both 2005 and 2007 in close proximity to eggs attached to the underside of cupped, newly expanded Prestonia seemannii leaves (Fig. 1a) on the western slope of Cerro Pelado, Gamboa (elevation 95 m, 9°7.29'N, 79°41.78'W). Eggs measured 3.5 × 0.9 mm and at first were an opaque, cherry-red, with the chorion becoming transparent and larvae distinguishable as development progressed. Clutches initially contained ten eggs with roughly ten new eggs added each day over the course of 3 to 5 days. The female became noticeably more defensive the second day of oviposition, straddling the eggs and jerking from side to side apparently in response to movement by the observer.

Larval emergence began on days 6 and 7 following first oviposition with clutches (n=3) at that time containing from 40-50 eggs. Within 24 hours after larvae began to emerge many of the original eggs were missing, apparently consumed by early-emerging larvae such that clutches were reduced to 8, 15 and 20 surviving larvae accompanied by some intact, opaque, less-developed eggs and opened eggs with red-colored residues of once-developing larvae visible under close inspection (Fig. 1). One day later an adult was observed (S.L.) returning to a natal group after having fallen from the plant on a detached leaf, then deposit a single egg which was immediately consumed by a nearby larva. First instar larvae (1.5-2.0 mm in length) had small black heads at the time of emergence, these easily distinguished them from second instar larvae appearing, 1 to 2 days later with red head capsules and a larger and more rotund appearance. Larvae expanded rapidly in size following their first meals but did not feed on leaf tissue until after the first molt, 2 to 3 days after emerging from the egg. Mothers at times tightly straddled their aggregated first and second instar larvae on the natal leaf, preventing their advance down the leaf petiole (Fig. 1b). While guarding, mothers reacted aggressively by charging to the edge of the leaf when a thin stick was introduced to the area by an observer. Charges, stamping and shaking continued for at least two minutes after the stimulus was presented and removed. The strongest reaction was given to a camera held approximately 10 cm under and to the side of the natal leaf. The mother seemed to be reacting to the camera lens–suggesting that a mirror held near guarding mothers might provide a non-invasive means of assessing defensiveness. On one occasion an Ectatomma tuberculatum (Olivier) worker was observed to pass by the base of the petiole, eliciting aggressive shaking of the natal leaf and short charges, after which the ant reversed course and departed that portion of the plant. As larvae became larger and began moving between leaves the intensity of the mothers’ reactions to foreign stimuli appeared to subside. Increasingly, mothers were seen feeding on leaves and leaf petioles, rather than guarding, as larval development proceeded.

Once the natal leaf was consumed, larvae began moving down the petiole to the stem, where they then moved either up or down in smaller groups to other leaves, sometimes moving as solitary individuals. Mothers, often fed from the pedicel of the leaf just consumed, occasionally accompanied by one or two larvae. Mothers actively trampled upon the backs of larvae still located on the pedicel, in effect pushing them away from the leaf and toward the stem. Mothers on other occasions stepped on and over larvae, rapidly tapping larvae with antennae and tarsi until they reversed direction. After leaving the natal leaf, mothers resumed guarding one of the several larval groups that reassembled. However, some groups continued to split into ever smaller units and moved to adjoining leaves and stems, leaving mothers guarding smaller sets of offspring and spending more time travelling among groups in what seemed to the observer as an effort to herd offspring back together (Fig. 1c). Mothers also increasingly divided their time between guarding and feeding on the cortex of the stem, girdling the vine over distances from a few cm to nearly 1 m. Seven days following eclosion larvae were arranged largely in doublets, girdling stems as intact leaves had disappeared in substantial sections of the plant. Larvae then descended in unguarded pairs to pupation sites by backing down the stem from which all cortex was stripped (Fig. 1d), effectively killing that section of the plant. By day eleven, most larvae had descended the host plant and moved along small above-ground roots into the leaf litter. One mother was last seen guarding two slow-developing larvae high (2 m) on the plant thirteen days after oviposition. Development from first oviposition to larvae wandering on the ground took approximately 20 days. Several larvae collected and placed in a plastic container with moist leaves, molted at day 4 and eclosed as teneral adults on days 18 and 19, a metamorphosis period slightly shorter than the 24 days estimated for Doryphora sp. near punctatissima by Eberhard (1981). Development from oviposition to the eclosion of adults in mid-June required 35 days. Monthly visits to the study area throughout the rest of the year were successful in finding solitary, feeding adults on nearby host plants but not in finding signs of additional reproductive activity. Thus, this species seems to have but a single generation per year timed to the period of accelerated leaf growth by its host plant. The nearly synchronous May onset of reproduction in both Doryphora paykulli in Panama and Doryphora sp. near punctatissima in Colombia ( Eberhard 1981) is likely the product of similar climate regimes in the two species’ ranges and subsequent effects on host phenology. Finally, the high morphological similarity of these neighboring species, the presence of larval cannibalism in both, but the presence of maternal care in only one, raises intriguing questions regarding the lability of defensive behaviors and underscores the importance of reconstructing phylogenetic relationships for as many Doryphora species as possible.