By Cotesia Flavipes

BIOLOGICAL CONTROL Parasitism and Location of Sugarcane Borer (Lepidoptera: Pyralidae) by Cotesia flavipes (Hymenoptera: Braconidae) on Transgenic and Conventional Sugarcane 1 2 3 M. SE´ TAMOU, J. S. BERNAL, J. C. LEGASPI, AND T. E. MIRKOV Biological Control Laboratory, Texas A&M University, College Station, TX 77843Ð2475 Environ. Entomol. 31(6): 1219Ð1225 (2002) ABSTRACT Location and parasitism of Diatraea saccharalis (F.) by Cotesia flavipes (Cameron) were compared between hosts fed either conventional or transgenic sugarcane expressing Galanthus nivalis L. agglutinin (GNA) under choice and no-choice conditions. In olfactometer experiments, females of C. flavipes randomly visited the different odor zones available but spent signiÞcantly more time in odor zones corresponding to plants damaged by D. saccharalis versus blank (control) odor zones. However, they spent similar amounts of time in odor zones corresponding to damaged transgenic and conventional sugarcane. Laboratory and Þeld-cage experiments showed that C. flavipes equally parasitized D. saccharalis feeding on transgenic and conventional sugarcane plants. Moreover, sex ratio and brood size of C. flavipes were similar on hosts fed transgenic or conventional sugarcane. The results of this study suggest that transgenic sugarcane expressing GNA would not signiÞcantly affect host location and parasitism of D. saccharalis by C. flavipes in the Þeld. KEY WORDS Diatraea saccharalis, snowdrop lectin, GNA, biological control, nontarget effects, sugarcane SUGARCANE BORER, Diatraea saccharalis (F.), was for from slightly negative, to nil, and positive (Se´tamou et many years the main insect pest of sugarcane in south al. 2002a). These results raised concerns that biolog- Texas. However, its populations declined substantially ical control of sugarcane borer could be compromised after successful colonization in the mid-1970s of the if GNA expressed in the transgenic sugarcane had larval parasitoid Cotesia flavipes (Cameron) and cur- signiÞcant host-mediated negative effects on the Þt- rently represent Ϸ5% of stalk borers recovered from ness of C. flavipes. Thus, the present and prior studies sugarcane Þelds (Legaspi et al. 1997, Meagher et al. sought to uncover any negative effects of transgenic 1998). At present, Mexican rice borer, Eoreuma loftini sugarcane expressing GNA on the Þtness and biolog- (Dyar), is the key insect pest of sugarcane in south ical control performance of C. flavipes (Se´tamou et al. Texas (Legaspi et al. 1999). Transgenic sugarcane ex- 2002b). Few studies have investigated the effects of pressing Galanthus nivalis L. agglutinin (GNA) at GNA delivered either via transgenic plants or artiÞcial Ϸ0.9% in leaves and stem tissue was developed to diet on natural enemies. Lethal effects of GNA were target Mexican rice borer because effective control not recorded for the twospotted lady beetle, Adalia methods against this pest are not currently available bipunctata Linnaeus, a predator of the green peach (Irvine and Mirkov 1997; Legaspi et al. 1997). Al- aphid Myzus persicae (Sulzer) (Birch et al. 1999, Down though the mode of action of GNA in insects is not et al. 2000). Similarly, direct detrimental effects of fully understood, it has been shown to interfere with GNA on the Þtness parameters of the potato aphid nutrient uptake by binding mannose in the midgut and parasitoid Aphelinus abdominalis Dalman were not thus affecting development (Powell et al. 1998, Down recorded, although the lectin indirectly reduced para- et al. 2000). sitoid size and proportion of females in the progeny Recent laboratory and Þeld studies showed that (Couty et al. 2001). In another study, Bell et al. (1999) GNA-expressing transgenic sugarcane negatively af- failed to Þnd adverse effects of GNA on the Þtness and fected various Þtness parameters of and damage levels parasitism success of the parasitoid Eulophus penni- caused by Mexican rice borer, whereas at the same cornis Nees. In a recent laboratory study, small neg- time, the effects on sugarcane borer were variable ative effects of GNA-expressing sugarcane were recorded on the development of C. flavipes parasitizing 1 E-mail: [email protected]. sugarcane borer (Se´tamou et al. 2002b). SpeciÞcally, 2 Department of Entomology, Texas Agricultural Experiment Sta- tion, Weslaco, TX 78596Ð8399. slight reductions in adult emergence rates and pro- 3 Department of Plant Pathology & Microbiology, Texas Agricul- portion of female offspring were evident in C. flavipes tural Experiment Station, Weslaco, TX 78596Ð8399. developing on hosts fed GNA-sugarcane relative to 0046-225X/02/1219Ð1225$02.00/0 ᭧ 2002 Entomological Society of America 1220 ENVIRONMENTAL ENTOMOLOGY Vol. 31, no. 6 those developing on hosts fed conventional sugarcane. Two month-old transgenic and conventional sugar- These Þndings raised additional concern over the pos- cane plants were individually infested with Þve sibility that biological control of sugarcane borer by C. fourth-instar sugarcane borers reared on artiÞcial diet flavipes might be disrupted following introduction of based on transgenic or conventional sugarcane tissue, GNA-sugarcane. Therefore, the goal of this study was respectively. The larvae were allowed to establish and to assess whether a number of host plant, host, and feed on the plants for 48 h before the experiment. parasitoid attributes important for biological control Ten-cm damaged stalk cuttings of transgenic or con- of sugarcane borer by C. flavipes are affected by GNA- ventional sugarcane were taken from the infested sugarcane. plants. The damaged cuttings were split longitudinally The current study speciÞcally addresses several to remove all feeding borers, and then placed with questions. (1) Are females of C. flavipes differentially frass in glass ßasks at one end of the olfactometer as an attracted to GNA- and conventional sugarcane plants odor source. In each test, damaged cuttings were used damaged by sugarcane borer? (2) Under no-choice as odor sources for two opposing olfactometer arms, conditions, are sugarcane borers fed GNA-sugarcane and the remaining two opposing arms corresponded to equally acceptable and suitable hosts as those fed blank controls. Individual females of C. flavipes were conventional sugarcane? (3) Under choice condi- released in the center of the olfactometer arena, and tions, are sugarcane borers fed GNA-sugarcane their activity was monitored for 10 min. The numbers equally acceptable and suitable hosts as those fed of visits and time spent in each odor zone were re- conventional sugarcane? And, (4) under Þeld-cage corded. In addition, a transverse line was drawn at 5 conditions, are females of C. flavipes reared on hosts cm from the end of each olfactometer arm, and tres- fed GNA-sugarcane equally capable of Þnding and pass of this line by a female was scored as its “Þrst parasitizing hosts as those reared on hosts fed con- choice.” A total of 100 females were tested in this ventional sugarcane? Addressing this latter question manner. The olfactometer was cleaned with 70% al- required the use of Þeld-cages and artiÞcial infesta- cohol, and odor sources were replaced and rotated tions of sugarcane borer because current levels of this after testing 25 females. pest in south Texas sugarcane are too low to permit a Parasitism Under No-Choice Conditions in the Lab- meaningful evaluation (Legaspi et al. 1997, Meagher et oratory. Ten-cm stalk cuttings of transgenic and con- al. 1998). ventional sugarcane were collected from 8 mo-old Þeld-planted sugarcane. The cuttings were immedi- Materials and Methods ately disinfected with 0.5% bleach solution for 5 min and rinsed twice with distilled water. Five cuttings Insects. All C. flavipes and sugarcane borer larvae from either transgenic or conventional sugarcane used in the experiments were obtained from labora- were placed individually in an oblique way in clear tory cultures maintained at the Texas Agricultural ϫ ϫ Experiment Station, Weslaco. The rearing methodol- plastic containers (10 10 10 cm) covered with a ogy for C. flavipes and sugarcane borer was described ventilated lid. Each cutting was infested with Þve in detail earlier (Se´tamou et al. 2002a, 2000b). fourth instar sugarcane borers reared on either trans- Plants. The sugarcane variety CP65Ð357was used genic or conventional sugarcane-based diet for the for all tests. Transgenic line 83 expressing GNA (Irvine corresponding treatment (Se´tamou et al. 2002a). and Mirkov 1997) and a nontransformed (convention- These larvae were allowed to establish within the stalk al) line were planted at the Texas Agricultural Exper- pieces for 24 h, after which two pairs of 24 h-old C. iment Station, Weslaco, in November 1999. Plants flavipes were released in each container. Thus, the were grown under standard farming practices and experimental set-up consisted of Þve containers per were ßood-irrigated once a month. conventional and transgenic sugarcane, each con- Plants used for the olfactometer tests were grown in tainer with one cutting, Þve sugarcane borers, and two the greenhouse in 7.56-liter pots Þlled with soil (Scotts pairs of C. flavipes. The containers were placed in a Ϯ Њ Metro Mix # 300, Marshville, OH). Ten-cm stalk cut- tray and kept at 25 1 C, 60Ð70% RH, and a 14:10 tings with at least one node were collected from 8 (L:D) photoperiod. Under these conditions, females mo-old Þeld planted canes and transplanted in the of C. flavipes live on average for 48 h (Se´tamou et al. pots. The pots were watered weekly until plants were 2002b). One week after parasitoid release, the stalk used in the tests. cuttings were split longitudinally to recover sugarcane Olfactometer Tests. A four-arm olfactometer built borer larvae. Recovered larvae were individually of four perspex crescents (90Њ arc, 27cm diam), similar reared on artiÞcial diet until formation of parasitoid to that of Vet et al. (1983) was used in this study. A cocoons or moth pupae. Parasitoid cocoons were in- ßask Þlled with distilled water was used to maintain air cubated until emergence of adult parasitoids. Upon humidity at 80Ð90% RH.

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