BioControl 48: 659–669, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands. Host suitability of the New World stalkborer Diatraea considerata for three Old World Cotesia parasitoids Robert N. WIEDENMANN1,∗,J.W.SMITH,JR.2 and Luis A. RODRIGUEZ-DEL-BOSQUE3 1Center for Economic Entomology, Illinois Natural History Survey, Champaign, IL 61820, USA; 2Department of Entomology, Texas A&M University, College Station, TX 77843, USA; 3Campo Experimental Río Bravo, INIFAP, Rio Bravo, Tamaulipas, Mexico 88900 ∗Author for correspondence; e-mail: [email protected] Received 23 October 2001; accepted in revised form 15 April 2003 Abstract. Biological control of stalkboring Lepidoptera often has been successful when the braconid parasitoids in the genera Cotesia and Apanteles were the natural enemies of choice. Constraints in using these gregarious, koinobiont, endoparasitoids have included host suita- bility, especially as influenced by the host’s immune response. The suitability of a novel host, the New World stalkborer Diatraea considerata (Lepidoptera: Pyralidae), for parasitization by three Old World braconids, Cotesia chilonis, C. flavipes and C. sesamiae (Hymenoptera: Braconidae), was compared to the suitability of another New World novel host, Diatraea saccharalis. D. considerata was less suitable for all three parasitoids than was D. saccharalis. The frequent occurrence of parasitized D. considerata larvae that did not yield parasitoids, or pupate within an appropriate time interval, suggested encapsulation of the parasitoid progeny, which was visible through the host cuticle. Given the suitability results, these three parasitoids would not be appropriate candidates for use against D. considerata. The results also have important implications for the narrow host range expressed by these parasitoids. Key words: Braconidae, Cotesia chilonis, Cotesia flavipes, Cotesia sesamiae, Diatraea, host range, host suitability, Hymenoptera, Lepidoptera, novel association, parasitoid, Pyralidae Introduction Successful biological control of pest insects using parasitic wasps requires that a host be ecologically and physiologically compatible with a parasitoid. Ecological compatibility ensures that the parasitoid successfully locates the host’s habitat and subsequently encounters a host in the microhabitat. Physiological compatibility ensures that the host attacked will be nutritionally suitable for parasitoid progeny growth and reproduction. With endoparasitic braconids, physiological compatibility further relies on the parasitoid over- coming host defenses, especially the host immune response. Reuniting pests with their indigenous natural enemies, commonly referred to as classical 660 ROBERT N. WIEDENMANN ET AL. biological control or an old association (Hokkanen and Pimentel, 1984), has relied on implied host-parasitoid compatibility formed during historical host- parasitoid interactions. However, novel-host-parasitoid pairings that occur through ecological equivalency or taxonomic relatedness of hosts, require that both ecological and physiological compatibility be tested explicitly (Wiedenmann and Smith, 1997, 1999). Stalkboring Lepidoptera have been the targets of numerous biological control attempts, using both old and novel associations (Bennett, 1965; Smith et al., 1993; Rodriguez-del-Bosque and Smith, 1997; Overholt, 1998). In one novel-association success, the New World pyralid, Diatraea saccharalis F. (sugarcane borer) has been controlled in several locations with the Old World microgastrine braconid, Cotesia flavipes Cameron, which originated from Asia (Alam et al., 1971; Simmonds, 1972; Meagher et al., 1998). This same parasitoid species has been imported into Africa for use against its old-association host, the pyralid Chilo partellus (Swinhoe); the parasitoid has established and subsequently expanded its range from the original colonization sites in eastern Africa (Overholt, 1998). Although C. flavipes successfully parasitizes D. saccharalis (Fuchs et al., 1979; Wiedenmann and Smith, 1995) and Diatraea lineolata (Walker) (Rodriguez-del-Bosque et al., 1990), attempts to use it against other New World pyralid stalkborers, such as Eoreuma loftini (Dyar), Diatraea grandiosella,andD. lineolata have been unsuccessful because of ecological and/or physiological incompatibility (Overholt and Smith, 1990; Rodriguez-del-Bosque et al., 1990; Meagher et al., 1998). Recent studies have attempted to elucidate patterns of physiological suitability among several novel stalkborer-parasitoid pairings of Old World parasitoids and New World stalkborers and the reciprocal pairings. Ecologi- cally equivalent, novel stalkborer-parasitoid pairings include stalkborers in the Old World genera Chilo Zincken and the New World Diatraea Guilding, and parasitoids in the Paleotropical braconid genus Cotesia Cameron and the related Neotropical Apanteles Foerster. Alleyne and Wiedenmann (2001a) showed differences in success among parasitoid species when three Paleo- tropical Cotesia (C. flavipes, C. sesamiae [Cameron], and C. chilonis Matsumura), which are part of the C. flavipes complex, parasitized the Neotropical stalkborer D. grandiosella, whereas all three parasitoids were similarly compatible with Neotropical D. saccharalis. In a parallel study, Ngi-Song et al. (1999) found physiological suitability inconsistent among the three Cotesia species as well as the two parasitoids, Apanteles deplanatus Muesebeck and A. minator Muesebeck, when parasitizing D. grandiosella, D. saccharalis, Chilo partellus and Chilo orichalcociliellus Strand. HOST SUITABILITY OF THE NEW WORLD STALKBORER 661 Diatraea considerata (Heinrich) is a stalkboring pyralid pest that attacks sugarcane (Saccharum officinarum L.) in west central Mexico. Within its indigenous distribution, i.e., the states of Colima, Jalisco and Nayarit (Box, 1951; Rodriguez-del-Bosque and Smith, 1989), D. considerata is commonly attacked by its putative ancestral parasitoid A. deplanatus (Austin and Dangerfield, 1989; Smith and Rodriguez-del-Bosque, 1994). Similarly, A. deplanatus also has been collected from its only other known host, Diatraea magnifactella Dyar, within this host’s indigenous distribution, but not from other Diatraea that are sympatric with D. considerata and D. magnifac- tella (Smith and Rodriguez-del-Bosque, 1994). Both D. considerata and D. magnifactella remain pests of sugarcane production in west central Mexico and are especially troublesome in areas where the indigenous parasitoid, A. deplanatus, does not occur (Smith and Rodriguez-del-Bosque, 1994). The Old World Cotesia spp. that attack lepidopteran stalkborers are considered to be ecologically equivalent to the New World Apanteles spp. that also attack lepidopteran stalkborers (Wiedenmann and Smith, 1997, 1999). Species attacking stalkborers from both parasitoid genera have equivalent life histories and foraging strategies (Smith and Wiedenmann, 1997). Both Apanteles and Cotesia are gregarious, endoparasitic, koinobiont, micro- gastrine braconids whose progeny are challenged by host defenses after oviposition (Wiedenmann and Smith, 1995). The foraging strategy of both parasitoid genera includes utilizing a series of synomone and kairomone cues emitted from infested host plants (Ngi-Song et al., 1996) and host frass (van Leerdam et al., 1985) to locate the host microhabitat. Foraging female parasitoids searching infested plants are initially attracted to the frass deposited at the entrance to the tunnel excavated by the stalkborer larvae, then enter the tunnel and attack the host (van Leerdam et al., 1985). Thus, the Old World Cotesia spp. that attack sympatric gramineous stalk- borers are ecologically very similar to the New World Apanteles spp. that attack Neotropical stalkborers, and are considered excellent candidates for importation as biological control agents against D. considerata. Testing a contrived host-parasitoid union, coupled with our continued quest to discover host suitability patterns for novel host-parasitoid pairings, generated the following research. We report findings on the suitability of D. considerata as a novel host for C. chilonis, C. flavipes,andC. sesamiae, and compare the host suitability to another novel, suitable host, D. saccharalis. Materials and methods The experimental parasitoids, Cotesia chilonis, C, flavipes and C. sesamiae were all reared similarly using D. saccharalis as the factitious host 662 ROBERT N. WIEDENMANN ET AL. (Wiedenmann et al., 1992), with the colony of each parasitoid species main- tained in isolation to prevent contamination. The C. flavipes colony originated as founders reared in D. saccharalis larvae collected from sugarcane in the lower Rio Grande Valley of Texas (van Leerdam et al., 1985), the C. chilonis colony originated as founders reared in Chilo suppressalis collected from rice in Japan, and the C. sesamiae colony originated as founders reared in C. orichalcociliellus collected from maize in Kenya. Pupae of D. considerata were collected from sugarcane fields near Los Mochis, Sinaloa, Mexico, and the emergent moths were allowed to oviposit on waxed-paper in a local laboratory. Fresh egg masses were subsequently shipped overnight to Entomology Quarantine at Texas A&M University, College Station, Texas. Emergent neonate larvae were placed onto artificial diet (Martinez et al., 1988) for rearing to the experimental host size. Larvae of D. saccharalis came from a laboratory culture maintained at Texas A&M University, using the same artificial diet. When larvae of both stalkborers