Entomologia Experimentalis et Applicata 82: 63–72, 1997. 63 c 1997 Kluwer Academic Publishers. Printed in Belgium. Mexican diabroticite beetles: II. Test for preference of cucurbit hosts by Acalymma and Diabrotica spp. Astrid Eben 13 , Mary E. Barbercheck 1 & Mart´ ın Aluja S. 2 1 Department of Entomology, Box 7634, North Carolina State University, Raleigh, NC 27695–7634, USA 2 Instituto de Ecolog´ ıa, Apartado Postal 63, 91000 Xalapa, Veracruz, M´ exico 3 Present address: Centro de Ecolog´ ıa, Apartado Postal 70–275, Universidad Nacional Aut´ onoma de M´ exico (UNAM), 04510 M´ exico, D.F., M´ exico Accepted: July 23, 1996 Key words: Acalymma, Diabrotica, cucurbitacin B, cucurbitacin E, coevolution Abstract Field collected adult diabroticites were offered three Cucurbita spp. in various combinations. Three Acalymma and five Diabrotica (Chrysomelidae: Luperini) species were tested in feeding choice and no-choice assays for their preference for bitter (cucurbitacin-containing) over non-bitter (without cucurbitacins) cucurbits, and for one of the two primary types of cucurbitacins. Tests were conducted in petri dishes and cages using plants in the cotyledon stage. All species significantly preferred the bitter over the non-bitter cucurbits (C. pepo L. var. Crookneck) in the tests offering a choice between cucurbitacin B-containing plants (C. pepo L. var. Ambassador) and no cucurbitacin- containing plants. Six species significantly preferred cucurbitacin E-containing plants (C. martinezii L. Bailey) over no cucurbitacin-containing plants. Cucurbitacin B-containing plants were significantly preferred over cucurbitacin E-containing plants. The previously observed preferences in choice tests no longer occurred in no-choice tests. In cage experiments, beetles did not show preferences for a certain cucurbit host. These observations are interpreted with regard to the kairomonal function of cucurbitacins for diabroticite beetles and the hypothesized evolutionary association between diabroticites and Cucurbitaceae. Introduction Leaf beetles of the family Chrysomelidae use a wide variety of plant allelochemicals for chemical protec- tion (DeRoe & Pasteels 1982; Rowell-Rahier et al. 1995). The preference for bitter Cucurbitaceae is well described for beetles in the tribe Luperini (Chambliss & Jones, 1966; Metcalf et al., 1982). Bitter second- ary compounds, the cucurbitacins (oxygenated tetra- cyclic triterpenoids), produced by many of the Cucur- bitaceae are highly toxic to mammals (David & Val- lance, 1955) and successfully deter non-adapted herb- ivores (DaCosta & Jones, 1971) but arrest leaf beetles of the of the genera Acalymma and Diabrotica (Rhodes et al. 1980; Howe et al., 1976). The strong affinity of polyphagous Diabrotica spp. and oligophagous Acalymma spp. to cucurbits has been described in numerous studies for beetle species occurring in North America, especially in the United States, and for Aulacophorina spp. in the Old World tropics (Metcalf et al., 1982; Raman & Annadurai, 1985). Diabroticites feed as adults on cotyledons, leaves and pollen of cucurbits, while larvae feed on roots. Cucurbits vary considerably in concentration of cucurbitacins among plant parts and among species (Metcalf et al., 1982). The genus Cucurbita produces as primary forms either cucurbitacin B or E. From these two types, all the other 18 cucurbitacins identified from Cucurbitaceae are derived. Highest concentrations of cucurbitacins are found in cotyledons, roots and fruits (Rehm et al., 1957). Several experimental studies have demonstrated that cucurbitacins act as arrestants and phagostimu- lants for diabroticites (Branson & Cuss, 1983; Met-