Influence of Drought Stress on Mexican Rice Borer
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Crop Protection 29 (2010) 415–421 Contents lists available at ScienceDirect Crop Protection journal homepage: www.elsevier.com/locate/cropro Influence of drought stress on Mexican rice borer (Lepidoptera: Crambidae) oviposition preference in sugarcaneq Allan T. Showler a,*, Boris A. Castro b,1 a USDA-ARS IFNRRU, Kika de la Garza Subtropical Agricultural Research Center, 2413 East Highway 83, Bldg. 201, Weslaco, TX 78596, USA b Texas A&M AgriLife Research and Extension Center, Weslaco, TX 78596, USA article info abstract Article history: Two sugarcane, Saccharum hybrids, varieties were grown in the greenhouse under well watered or Received 4 June 2009 drought conditions to examine the influences of stress on Mexican rice borer, Eoreuma loftini (Dyar), Received in revised form oviposition preference and selected nutritional components without impinging factors common to field 27 July 2009 conditions that alter responses. Our research revealed that, under controlled conditions, drought induced Accepted 29 July 2009 a wider range and greater uniformity of free amino acid (FAA) accumulations than have been previously reported. Drought stress resulted in increased dry leaf tissue and elevated concentrations of 7 of 9 Keywords: detectable free essential (for insect health) amino acids in stalks, the chief food of Mexican rice borer Eoreuma loftini Free amino acids larvae. Stressed sugarcane was preferred for oviposition, likely related to greater numbers of dry leaves Host plant selection and heightened host plant nutritional quality. Dry leaf tissue, which is not consumed, may be a cue for Resistance improving chances of larvae encountering nutrient-enhanced living tissue, and for concealing eggs in Water deficit folds. Excised dry leaf tissue from the treatments was indistinguishable for oviposition preference; therefore, biochemical status of living tissue may provide oviposition cues. Varieties exhibited no major genotypic differences in FAA accumulations or oviposition preference. Published by Elsevier Ltd. 1. Introduction It was projected to arrive in Louisiana during 2008 and to infest all of the state’s rice and sugarcane production areas by 2035 (Reay- The Mexican rice borer, Eoreuma loftini (Dyar), originally from Jones et al., 2008). While insecticides can reduce Mexican rice borer Mexico, has been the key pest of sugarcane, Saccharum spp. hybrids, injury to sugarcane, yield increases have not often been reported in south Texas since spreading there in 1980 (Johnson and Van (Johnson, 1985; Meagher et al., 1994; Legaspi et al., 1999b), and use Leerdam, 1981) where it represents >95% of the stalk borer pop- for Mexican rice borer control in Texas was discontinued (Legaspi ulation (Legaspi et al., 1999a). The pest’s distribution has extended et al., 1997). Classical biological control using parasitoids also failed into the rice, Oryza sativa L., production region of east Texas (Meagher et al., 1998), but varietal resistance has shown some (Browning et al., 1989; Reay-Jones et al., 2007b), presumably promise (Reay-Jones et al., 2003, 2005, 2007a). assisted by >15 species of North American alternate host plants Infestations are especially severe where soil is saline (Reay- (Van Zwaluwenberg, 1926; Osborn and Phillips, 1946; Johnson, Jones et al., 2003), and under conditions of water deficit (Meagher 1984; Browning and Hussey, 1987) including other economically et al., 1993; Reay-Jones et al., 2005). Accumulation of plant free important crops such as corn, Zea mays L., sorghum, Sorghum amino acids (FAAs) and other nutrients is influenced by drought bicolor L. Moench, and rice (Van Zwaluwenberg, 1926; Osborn and (Rabe, 1994; Gzik, 1996; Showler, 2002, 2004; Showler et al., 2007), Phillips, 1946; Youm et al., 1988; Rodriguez-del-Bosque et al., 1996). including in sugarcane (Muquing and Ru-kai, 1998). Availability of amino acids is an important factor for growth, development, host selection, and reproduction of many herbivorous arthropods q Mention of trade names or commercial products in this publication is solely for (McNeil and Southwood, 1978; Showler, 2001, 2004; Nation, 2002), the purpose of providing specific information and does not imply recommendation and population buildups of some insect pests are linked to drought or endorsement by the U.S. Department of Agriculture. stress (Brodbeck and Strong, 1987; Ruberson et al., 1994; Mattson * Corresponding author. Tel.: 1 956 969 4882; fax: 1 956 969 5024. þ þ and Haack, 1991). The purpose of this study was to determine, E-mail address: [email protected] (A.T. Showler). 1 Present address: Dow AgroSciences, 7521 West California Ave., Fresno, CA under controlled greenhouse conditions, the influence of water- 93706, USA. deficit stress and two commonly grown cultivars on Mexican rice 0261-2194/$ – see front matter Published by Elsevier Ltd. doi:10.1016/j.cropro.2009.07.014 416 A.T. Showler, B.A. Castro / Crop Protection 29 (2010) 415–421 borer oviposition preference and on plant nutritional quality in treatment per assay). The juice (10–15 ml) was thoroughly mixed terms of FAAs absent extraneous impinging factors common to field for 2 min using a Virtishear homogenizer (Virtis, Gardiner, NY, conditions. USA). 5 ml from each sample was placed in separate 10 ml tubes and centrifuged at 10 000 rpm for 30 min. The extract samples 2. Materials and methods were stored at À80 C. 1 ml of supernatant from each sample was filtered through a 0.5 mm filter fitted to a 5 ml plastic syringe. 2.1. Large cage experiment – oviposition preference, whole plants Samples were placed in the autosampler of an Agilent 1100 Series (Agilent Technologies, Atlanta, GA, USA) reversed-phase high- Single sugarcane plants were grown from seed pieces in 7.6-l performance liquid chromatograph (HPLC) with a binary pump pots until they reached 1.2 m in height (9 nodes) in a greenhouse at delivering solvent A [1.36 g sodium acetate trihydrate þ 500 ml the USDA-ARS Kika de la Garza Subtropical Agricultural Research purified HPLC grade water þ 90 ml triethylamine (TEA) þ sufficient Center in Weslaco, Hidalgo County, Texas. The soil was Sunshine acetic acid to bring the pH to 7.2] and solvent B [1.36 g sodium mix no. 1 nursery potting soil (w75% sphagnum peat moss, perlite, acetate trihydrate þ 100 ml purified HPLC grade water (acetic acid dolomitic limestone, and gypsum; Sungro Horticulture, Bellevue, added to this mixture to bring the pH to 7.2) þ 200 ml acetoni- Washington). When the plants reached the two-leaf stage, 200 ml trile þ 200 ml methanol] at 100 and 1.0 ml/min on a Zorbax Eclipse of Peters Professional (Scotts-Sierra Horticultural Products AAA 4.6  150 mm 3.5m column (Agilent Technologies). Absor- Company, Marysville, OH) water-soluble general purpose 20–20– bances at 262 and 338 nm were monitored on a variable wave- 20 N–P–K fertilizer at 15.8 g/l of water was applied to the soil. Half length detector for 48 min per sample. The autosampler measured of the plants were variety L97-128 (not regarded as being resistant and mixed 6 ml sodium borate buffer (0.4 N, pH 10.2 in water), 1 ml to the sugarcane borer, Diatraea saccharalis [F.] (White et al., 2008), 9-fluorenylmethylchloroformate (FMOC), and 1 ml ophthalaldehyde and not listed in the literature as being resistant to the Mexican rice (OPA) derivitizing agents, and 2 ml of sample, then injected 2 ml for borer) and the other half were variety CP70-321 (resistant to the chromatographic separation of FAAs. Identification and quantifi- sugarcane borer (Bessin et al., 1990) and to the Mexican rice borer cation of 17 derivitized FAAs (alanine, arginine, aspartic acid, (Pfannenstiel and Meagher, 1991; Legaspi et al., 1999a)). Twelve cystine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, pots of each variety were placed within 3 m  1.2 m  1.8 m methionine, phenylalanine, proline, serine, threonine, tyrosine, and (l  w  h) cages (36 mesh/cm2) inside the greenhouse. Six plants valine) were achieved by calibrating with a standard mixture of of each variety were well watered and the other six were drought amino acids. Peak integration accuracy was enhanced by manual stressed. Soil in the well watered pots was kept constantly moist establishment of peak baselines using Agilent software. Results are with infusions of water as needed. The drought stressed plants presented as picomoles of FAA per microliter of juice. received only 2000 ml of water at the beginning of each week in Differences among the four treatments were found using one- a single pulse. The two watering regimes were implemented when way ANOVA and means were separated using Tukey’s HSD the plants were 1.2 m tall and for the next 6 wk before the assays (Analytical Software, 1998). Because the assays were conducted in commenced. Six replicates of each variety-irrigation treatment different cages and at different times, the data from the assays were combination were arranged in a randomized complete block not pooled. Overall differences between varieties or irrigation design. The experiment was repeated three times, and each, regimes were detected using a 2  2 factorial design (Analytical referred to as assays 1, 2, and 3, was conducted z1 mo apart from Software, 1998). the other assays and in different cages. Adult Mexican rice borers were collected as larvae in commer- 2.2. Small cage experiment 1 – oviposition preference for dry leaf cial sugarcane fields in Hidalgo County to generate a colony of tissue, all four treatments Mexican rice borers at the Texas A&M University System’s AgriLife Research and Extension Center in Weslaco. The colony was reared Sugarcane plants were grown under the same treatment on artificial diet (Martinez et al., 1988)at25C, 65% RH, and conditions as in the whole plant assays. To test whether dry leaf a photoperiod of 14:10 (L:D).