Eoreuma Loftini Research Articles

Fortuitous Antixenosis in Transgenic Sugarcane: Antibiosis-Expressing Cultivar Is Refractory to Ovipositing Herbivore Pests

The ovipositional preferences of two stemboring pests, Eoreuma loftini Dyar and Diatraea saccharalis (F.) (Lepidoptera: Pyralidae), were evaluated in choice tests on transgenic sugarcane expressing Galanthus nivalis agglutinin (GNA) and the corresponding conventional near- isogenic sugarcane. Differences in various host-selection indices indicated that both D. saccharalis and E. loftini preferentially laid eggs on conventional sugarcane versus the transgenic cultivar. A signif- icantly higher proportion of leaves per plant were allocated eggs on conventional relative to transgenic sugarcane plants by both D. saccharalis and E. loftini. In addition, larger proportions of both total eggs and egg masses laid by females were allocated to conventional (66 Ð71%) relative to transgenic (29 Ð34%) sugarcane, but the size of egg masses of both stemborer species did not vary with plant type. An oviposition preference index, computed as the ratio of the difference in egg loads (eggs or egg masses) allocated to transgenic or conventional plants and the total number of eggs laid, indicated that transgenic sugarcane plants were refractory to ovipositing E. loftini and D. saccharalis. However, differences in host-selection indices for transgenic and conventional sugarcane plants in D. saccharalis were associated largely with the presence of the transgene (i.e., plant type), while differences in E. loftini were associated largely with plant morphological characteristics related with plant type. The unintended antixenotic effects of transgenic sugarcane observed in this study are important because they highlight the validity of concerns over unanticipated consequences of releasing transgenic plants before intensive evaluation.

Effects of snowdrop lectin on Mexican rice borer (Lepidoptera: Pyralidae) life history parameters.

The effects of the snowdrop lectin, Galanthus nivalis agglutinin (GNA), delivered through an artificial diet, on growth, development, and life history parameters of the Mexican rice borer, Eoreuma loftini (Dyar), were evaluated in the laboratory. Incorporation of GNA at three treatment levels, 0.5, 1.0, and 2.0% of total dietary protein, in the larval diet significantly decreased larval survivorship and percentage of adults emerging relative to a control diet lacking GNA, whereas differences were not observed among the three treatment levels. Both larvae and pupae in the control were 8-25% larger than those in the GNA treatments, but differences were not observed between larvae in the GNA treatments. Furthermore, presence of GNA did not affect larval and pupal developmental periods, longevities, and fecundities compared with the control. Mexican rice borer life history parameters, such as net reproductive rate and intrinsic rate of increase, were substantially reduced by the presence of GNA in the diet, but differences were not evident among the three GNA treatment levels.

Effects of GNA transgenic sugarcane on life history parameters of Parallorhogas pyralophagus (Marsh) (Hymenoptera: Braconidae), a parasitoid of Mexican rice borer.

Parallorhogas pyralophagus (Marsh) is the principal parasitoid of the Mexican rice borer [Eoreuma loftini (Dyar)], the primary pest of sugarcane in south Texas. Insect resistant transgenic sugarcane producing Galanthus nivalis agglutinin (GNA) was developed to improve control of E. loftini. The present laboratory study addressed whether over two consecutive generations transgenic sugarcane delivered via artificial diet has adverse host-mediated effects on P. pyralophagus life history parameters. The results of this study showed that a number of life history parameters were affected by transgenic sugarcane, whereas others were not affected, and that effects varied between generations. In the first generation, adult longevity was increased by approximately 2 d, and cocoon to adult and egg to adult developmental times were prolonged by approximately 1 d in parasitoids exposed to transgenic sugarcane, whereas effects were not evident on adult size; egg load; egg to cocoon developmental time; rates of gain of longevity and egg load with adult size; and egg, larval, and pupal mortality. However, in the second generation, adult longevity was reduced by approximately 3 d, adult size by approximately 5%, egg load by approximately 24%, and rate of gain of longevity with adult size by approximately 21%, whereas effects were not evident on the rate of gain of egg load with adult size. It was concluded that although GNA transgenic sugarcane, ingested via E. loftini tissues, was not acutely toxic to P. pyralophagus, the sublethal effects on life history parameters measured in this study must be considered in a broader context to determine their possible ecological significance.

Effects of Snowdrop Lectin on Mexican Rice Borer (Lepidoptera: Pyralidae) Life History Parameters

The effects of the snowdrop lectin, Galanthus nivalis agglutinin (GNA), delivered through an artificial diet, on growth, development, and life history parameters of the Mexican rice borer, Eoreuma loftini (Dyar), were evaluated in the laboratory. Incorporation of GNA at three treatment levels, 0.5, 1.0, and 2.0% of total dietary protein, in the larval diet significantly decreased larval survivorship and percentage of adults emerging relative to a control diet lacking GNA, whereas differences were not observed among the three treatment levels. Both larvae and pupae in the control were 8-25% larger than those in the GNA treatments, but differences were not observed between larvae in the GNA treatments. Furthermore, presence of GNA did not affect larval and pupal developmental periods, longevities, and fecundities compared with the control. Mexican rice borer life history parameters, such as net reproductive rate and intrinsic rate of increase, were substantially reduced by the presence of GNA in the diet, but differences were not evident among the three GNA treatment levels.

Effect of Temperature on the Life Cycle ofLydella jalisco(Diptera: Tachinidae), a Parasitoid ofEoreuma loftini(Lepidoptera: Pyralidae)

The effect of temperature on development, survival, and adult longevity of Lydella jalisco Woodley (Diptera: Tachinidae), a parasitoid of the Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Pyralidae), was studied under laboratory conditions. Development times of L. jalisco larvae and pupae decreased with temperatures in the range 15–35°C. However, survival was greater at cooler temperatures similar to those encountered in the parasitoid’s native habitat; percentage of adult emergence was 62.5% at 20°C compared with 9.5% at 35°C. The lower temperature threshold for development of larvae was 14.5°C, whereas for pupae it was 13.8°C. Adult lifespan was also affected by high temperatures. Adult parasitoids lived 20 to 25 d at temperatures in the range 15–25°C, whereas they lived 4 to 6 d at 35–40°C. For <10 consecutive hours, temperatures exceeding 30°C prevail in the Lower Rio Grande Valley of Texas during the months of May through September when populations of E. loftini reach an economic threshold. Therefore, the potential efficacy of L. jalisco as a biological control agent of E. loftini in south Texas should be examined closely because mated females of L. jalisco require 7–14 d for maximum egg fertilization and embryonic development.

Evaluation of lectin-expressing transgenic sugarcane against stalkborers (Lepidoptera: Pyralidae): effects on life history parameters.

The impact of snowdrop lectin (Galanthus nivalis agglutinin, GNA) expressed in transgenic sugarcane on life history parameters of Mexican rice borer [Eoreuma loftini (Dyar)] and sugarcane borer [Diatraea saccharalis (F.)] (both Lepidoptera: Pyralidae) was evaluated. In the laboratory, lyophilized sugarcane leaf sheath tissue was incorporated in a meridic diet resulting in a GNA concentration of 0.47% of total protein, and used for insect bioassays over two successive generations. Deleterious effects of GNA were not observed on survival, weight, and developmental periods of larvae and pupae, nor on adult fecundity and egg viability of D. saccharalis. Moreover, in the first generation, addition of transgenic sugarcane tissue to the diet enhanced larval growth in D. saccharalis resulting in higher larval and pupal weight compared with diet with nontransgenic sugarcane, but this effect was not observed in the second generation. In contrast, larval survival, percent adult emergence, and female fecundity of E. loftini were significantly reduced when fed transgenic sugarcane diet compared with nontransgenic sugarcane diet. In addition, a substantial reduction of female pupal weight of E. loftini was observed in the second generation. For both species, the only consistent effect of GNA in both generations was a reduction in adult female longevity. Life table parameters showed that GNA at the level found in the transgenic diet negatively affected development and reproduction of E. loftini, whereas it had a nil to positive effect on development and reproduction of D. saccharalis.

Effects of Snowdrop Lectin (&lt;I&gt;Galanthus nivalis&lt;/I&gt; Agglutinin) Expressed in Transgenic Sugarcane on Fitness of &lt;I&gt;Cotesia flavipes&lt;/I&gt; (Hymenoptera: Braconidae), a Parasitoid of the Nontarget Pest &lt;I&gt;Diatraea saccharalis&lt;/I&gt; (Lepidoptera: Crambidae)

Cotesia flavipes (Cameron) is a parasitoid responsible for maintaining populations of sugarcane borer, Diatraea saccharalis (F.), below economic levels in south Texas sugarcane Þelds. Transgenic sugarcane expressing the snowdrop lectin (Galanthus nivalis agglutinin, GNA) was developed against the Mexican rice borer, Eoreuma loftini (Dyar), the primary pest of south Texas sugarcane. The potential impact of GNA-expressing sugarcane on various biological and Þtness parameters of Cotesia flavipes (Cameron) was studied in the laboratory to gain insight on likely effects of the transgenic sugarcane on biological control of sugarcane borer by C. flavipes. Females of C. flavipes were offered sugarcane borer larvae fed one of two diet treatments for oviposition for two successive generations: (1) artiÞcial diet containing transgenic sugarcane tissue or (2) artiÞcial diet containing nontransgenic sugarcane tissue. Small to marginal negative effects of artiÞcial diet con- taining transgenic sugarcane tissue were evident in the rate of host suitability, number of cocoons and adult parasitoids emerging per host, percentage cocoons yielding parasitoids, and sex ratio and adult lifespan of parasitoids. These effects were variable between the two parasitoid generations examined. In contrast, differences were not detected between diet treatments in rates of host acceptance, egg load of females, and egg to adult developmental periods. The negative effects of transgenic sugarcane on C. flavipes detected in this study are important because GNA levels in the diet (0.49% of total protein content) containing transgenic sugarcane tissue were 50% of the level expressed in trans- genic sugarcane plants. Results are discussed in relation to potential impacts of the transgenic cultivar on biological control of sugarcane borer by C. flavipes.

Impacts of Developing on Bt Maize-Intoxicated Hosts on Fitness Parameters of a Stem Borer Parasitoid

Transgenic Bt maize cultivars are widely used in U.S. agriculture. Control of target pests by these cultivars is not complete, and non-target pests are usually tolerant of the toxic activity of these cultivars. Sublethally intoxicated pest individuals may become hosts for parasitoids, but their quality as hosts may be affected as a result of intoxication. This study addresses the effects on various fitness parameters in parasitoids that develop on intoxicated hosts. The parasitoid used in this study was Parallorhogas pyralophagus (Marsh), a gregarious, external idiobiont, and the host was Eoreuma loftini Dyar, a subtropical stemborer. Results showed that ingestion of Bt maize tissue by E. loftini larvae negatively affected some fitness components in P. pyralophagus, whereas other components were not affected. Specifically, immature stage developmental mortality was greater, adult longevity was approximately 1 d shorter in females, and developmental times were approximately 2 d longer in both males and females when P. pyralophagus developed on hosts fed Bt maize tissue relative to hosts fed non-Bt maize tissue. Moreover, parasitoid brood size was positively correlated with host size when hosts were fed non-Bt maize tissue, while this relationship was absent when hosts were fed Bt maize tissue. However, feeding on Bt maize tissue did not affect egg loads, adult size-egg load and adult size-longevity relationships, adult sizes of females and males, and sex ratio of parasitoids whose hosts were fed Bt maize tissue. Results are discussed in relation to the importance of sublethal effects of Bt maize cultivars on parasitoids and potential impacts on naturally-occurring biological control.

Effects of Age and Host Number on Reproductive Biology ofAllorhogas pyralophagus(Hymenoptera: Braconidae) Attacking the Mexican Rice Borer (Lepidoptera: Pyralidae)

Abstract Laboratory studies were conducted to determine the effects of parasitoid age and number of hosts available on selected attributes of parasitoid reproduction. Newly emerged mated females of the gregarious parasitoid Allorhogas pyralophagus Marsh were divided into groups ranging in age from 5 to 12 d. For each age class, individual females were exposed to one, two, four, and eight hosts of the Mexican rice borer, Eoreuma loftini (Dyar), over a 24-h period. For each age class, number of eggs laid and hosts attacked were fitted to nonlinear oviposition models and type II functional response curves, respectively. Numbers of eggs laid per female per day were highest at ≈20 eggs per day in 6-d-old females, declining to ≈5 per day in 12-d-old females. The functional response curves showed declining attack rates with time, from ≈2.0 hosts per day in 5-d-old females, to ≈1.0 in 12-d-old parasitoids. Percentage of progeny emergence was not affected by either parasitoid age or number of hosts available. Perc...

Life-history studies of Lydella jalisco (Diptera: Tachinidae), a parasitoid of Eoreuma loftini (Lepidoptera: Pyralidae)

Lydella jalisco Woodley (Diptera: Tachinidae) is a solitary endoparasitoid of the Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Pyralidae), the key pest of sugarcane in Texas. This parasitoid was re-introduced into Texas in 1998 as part of a classical biological control program. Information on the biology of L. jalisco is scarce and indispensable for its propagation in captivity and understanding of L. jalisco-E. loftini interactions. Parasitoid longevity, reproductive biology and immature development were studied under laboratory conditions. At 22 °C, honey-fed mated adults lived about two weeks whereas lifespan of unmated individuals averaged three weeks. Females of L. jalisco emerged with a complement of eggs that continued to develop during the first days following emergence. Mating was necessary for embryonic development. After copulation, eggs were fertilized and gradually transferred to an elongated ovisac where they incubated for about one week before hatching. Hatching occurred in the female's reproductive tract, an attribute of true ovoviviparous reproduction. First instar larvae were available for oviposition during the female's entire lifetime. Egg load increased with adult female size; mean lifetime potential fecundity was 400 ± 140 eggs per female. Parasitoids successfully developed on second to sixth instar host larvae. However, host size at parasitization positively influenced the size of resultant adult parasitoids as well as the duration of the larval growth period which was shorter as host size increased. Parasitoid larvae did not complete development below 15 °C, whereas parasitoid larval and pupal mortality respectively reached 14 and 75 percent when temperature exceeded 30 °C. The importance of biological and reproductive attributes of L. jalisco for biological control, as well as for rearing are discussed.

Evaluation of Steinernema riobravis (Nematoda: Steinernematidae) Against the Mexican Rice Borer (Lepidoptera: Pyralidae)

The virulency of an endemic nematode, Steinernema riobravis Cabanillas, Poinar and Raulston (Nematoda: Steinernematidae), was tested against the Mexican rice borer, Eoreuma loftini(Dyar) (Lepidoptera: Pyralidae), in the laboratory and field. Steinernema riobravis caused 100% mortality in E. loftini larvae at all concentrations of 20 to 240 nematodes per larva 2 d post treatment. Numbers of juvenile progeny increased significantly with inoculum dosage of nematodes. Average juvenile progeny ranged from 2,000 per borer larva at 10 nematodes per larva to over 4,000 per larva at 120 per larva. A field experiment on sugarcane (Saccharum spp. cv ‘NCo 310’) was performed using three treatments: (1) control (no nematodes); (2) low application rate (1.24 × 109 nematodes/ha); and, (3) high application rate (2.47 × 109 nematodes/ha). At weekly intervals, the field was sampled for numbers of internodes per stalk, numbers of internodes damaged by borer larvae, and parasitoids reared from larvae collected. The field results showed the nematode treatments were ineffective in reducing borer incidence or damage. Percentage of bored internodes and numbers of borers collected significantly increased with time, but treatment effects were not significant. Numbers of parasitoids emerging from the larvae collected were too low to be analyzed statistically. Plant height, aboveground biomass, and juice quality were not significantly affected by treatment. The ineffectiveness of the nematode applications may be due to desiccation caused by exposure to sunlight and inadequate humidity, as well as poor contact with the target insect.

Laboratory and field evaluation of Beauveria bassiana against sugarcane stalkborers (Lepidoptera: Pyralidae) in the lower Rio Grande Valley of Texas.

Of approximately 18,200 ha planted to sugarcane in south Texas, only approximately 80 ha (<0.5%) are treated with insecticides because this type of control is widely regarded as ineffective against stalkboring pyralids, the key pests of sugarcane. Therefore, nonchemical control measures, such as resistant varieties and biological controls, must be evaluated to mitigate the losses caused by stalkborers. We performed laboratory and field evaluations on the use of Beauveria bassiana (Balsamo) Vuillemin (Deuteromycotina: Hyphomycetes) (strain GHA) against the Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Pyralidae), which causes damage in south Texas estimated at between 10 and 20 million dollars annually. We also performed bioassays against the sugarcane borer, Diatraea saccharalis (F.) (Pyralidae), the key pest in other sugarcane growing areas. In the bioassays, E. loftini was substantially more susceptible to B. bassiana than D. saccharalis, based on both 5-d LD50 values and survival times. A commercial oil-based formulation of B. bassiana was evaluated in the field using the following treatments: oil alone (control), B. bassiana + oil, and B. bassiana + Silwet L-77 carrier at an application rate of 5 x 10(13) spores per hectare. Neither numbers of E. loftini per stalk, nor stalk damage (approximately 20% bored internodes) were significantly affected by treatment. The application of B. bassiana + Silwet significantly affected the numbers of internodes showing high damage, but not those with low or medium damage. Analysis of yield data and juice quality showed no significant treatment effects. We conclude that the application of Beauveria + Silwet offers the best chances for reducing damage caused by E. loftini of those treatments tested. However, reductions in insect incidence or damage did not result in measurable increases in yield or sugar quality, probably because of insufficient coverage. Effective control of stalkboring pyralids in sugarcane using B. bassiana will likely require improvements in delivery technology.

Vertical Distribution of Mexican Rice Borer (Lepidoptera: Pyralidae) Larvae and Tunnels in Lower Rio Grande Valley Sugarcane

Vertical distribution patterns of Mexican rice borer, Eoreuma loftini (Dyar), larvae and tunnels in Lower Rio Grande Valley sugarcane, Saccharum spp., were examined by stalk dissections in commercial sugarcane from late May until early September (1992) or mid-October (1993). Larval age distributions were fairly stable throughout the sampling periods, with small larvae consistently comprising a substantial portion of the larval population infesting millable stalks. Meaningful differences in the vertical distributions of small, medium, and large larvae were not detected. Contrary to earlier reports, most larvae and tunnels were located in the lower, more productive internodes regardless of the degree of stalk development. These results do not support the concept of age-specific internode susceptibility to Mexican rice borer attack, and stress the need to consider season-long population suppression in the development of strategies to manage the Mexican rice borer in sugarcane.

Laboratory and Field Evaluations of Biorational Insecticides Against the Mexican Rice Borer (Lepidoptera: Pyralidae) and a Parasitoid (Hymenoptera: Braconidae)

We compared laboratory and field efficacies of pyrethroid insecticides (Baythroid, ‘FCR 4545’ [both cyfluthrin], Karate [lambda cyhalothrin]) and insect growth regulators (Confirm [tebufenozide], ‘RH-2485’ [methoxyfenozide]) against the Mexican rice borer, Eoreuma loftini (Dyar), a key pest of sugarcane in south Texas. We also studied treatment effects on longevity and survivorship of its braconid parasitoid, Allorhogas pyralophagus Marsh. In the 1996 field season, Baythroid resulted in lower percentages of bored internodes compared with the other treatments. In the 1997 season, less borer damage was found in ‘FCR 4545’ (an isomer of Baythroid), relative to the other treatments. The differences may be partially attributed to the different application methods (tractor sprayer versus aerial). In both field seasons, no significant treatment effects could be found in any of the yield or juice quality measurements, suggesting that improvements must be made in application technology, or the biorational insecticides must be used in conjunction with other control agents, such as biological controls. Efficacy may be improved if applications can be timed to windows of susceptibility based on either plant phenology or pest lifecycle. Baythroid and FCR 4545 were generally most effective in reducing damage caused by E. loftini, although residual toxicity of Baythroid was higher than FCR 4545 against both E. loftini and A. pyralophagus. Comparisons between similar bioassays showed that Baythroid and tebufenozide were more toxic to E. loftini than to A. pyralophagus. Therefore, if A. pyralophagus or a similar parasitoid were to be used in conjunction with an insecticide, an effective approach may be to use a less toxic biorational, such as the insect growth regulator tebufenozide, or to time the release of the parasitoids after residual toxicity has declined in a biorational such as FCR 4545.

Sugarcane Stemborers and Their Parasites in Southern Texas

Approximately 40,000 stemborer larvae, pupae, and parasite cocoons were collected during 1982–1995 from commercial sugarcane fields and allowed to complete development under laboratory conditions. Eoreuma loftini (Dyar) and Diatraea saccharalis (F.) comprised 92.4% (36,897/39,945) and 5.2% (2,057/39,945) of the stemborers collected. More than 65% of field-collected stem borer larvae completed development and emerged as adults after being transferred to artificial diet; however, 27.5% died during development. Average seasonal parasitization of E. loftini larvae and pupae (including parasites collected during sampling and those that completed development) was 6.2 ± 1.0%. The most numerous parasites collected from E. loftini included 2 indigenous braconids, Chelonus sonorensis Cameron and Digonogastra solitaria Wharton & Quicke, and 2 exotic braconids, Alabagrus stigma (Brulle) [ =Agathis stigmatera (Cresson)] and Allorhogas pyralophagus Marsh. Average seasonal parasitization of D. saccharalis was 8.9 ± 1.6%, caused mostly by Cotesia flavipes (Cameron).

Evaluation of Trichogramma spp. (Hymenoptera: Trichogrammatidae) Against Two Pyralid Stemborers of Texas Sugarcane

The role of Trichogramma minutum Riley (reared on Helicoverpa zea [Boddie] eggs or on an artificial diet) and T. pretiosum Riley (reared on H. zea eggs) as parasitoids of the Mexican rice borer, Eoreuma loftini (Dyar) and sugarcane borer, Diatraea saccharalis (F.), was assessed under laboratory and greenhouse conditions. The laboratory results showed that T. minutum reared on H. zea eggs parasitized 52.5% of Mexican rice borer eggs, compared to 50.3% for T. pretiosum. Parasitization of Mexican rice borer eggs by T. minutum reared on the artificial diet (62.6%) was not significantly different compared to those reared on H. zea eggs (52.5%). Trichogramma minutum reared on H. zea eggs parasitized 42.0% of sugarcane borer eggs, compared to only 12.6% by T. pretiosum. About 43.4% of sugarcane borer eggs were desiccated, despite 80 to 85% RH. Percentages of emergence (83.0%), female progeny (67.0%), deformed females (3.3%), and development time (8.2 d) in T. pretiosum reared from Mexican rice borer eggs did not differ significantly from those reared on H. zea eggs (91.3%, 72.5%, 2.5%, 8.3 d, respectively). However, T. pretiosum females reared from Mexican rice borer had greater longevity (2.5 d) and body length (0.385 mm) than females reared on H. zea (1.6 d, 0.326 mm, respectively). In the greenhouse, T. pretiosum parasitized an average of 55.3% of the Mexican rice borer eggs (egg masses were distributed on the sugarcane plants). About 21.0% of the eggs were dessicated, probably due to puncturing by the parasitoid, compared with 4.5% in the control, where egg masses were distributed on the plants without release of Trichogramma. Our results show the potential for use of Trichogramma spp. to control sugarcane stalk borers in a field IPM program.

Biological Control of Maize and Sugarcane Stemborers in Mexico: A Review

Surveys for natural enemies of Mexican stemborers and the major biocontrol attempts using indigenous and exotic parasites in Mexico are reviewed. Although biological control of stemborers in Mexico was initiated in the 1920s, parasite explorations were intensified during the 1980s and have continued to date in response to the invasion of Diatraea grandiosella Dyar, D. lineolata (Walker) and Eoreuma loftini (Dyar) into the United States from Mexico. Recent surveys for stemborer parasites in Mexico has led to the discovery and laboratory culturing of the braconids Allorhogas pyralophagus Marsh, Digonogastra solitaria Wharton & Quicke and Macrocentrus prolificus Wharton; the ichneumonid Mallochia pyralidis Wharton and the tachinid Lydella jalisco Woodley. The Asian braconid Cotesia flavipes Cameron was introduced and established in the states of Tamaulipas and Sinaloa against Diatraea spp. Unsuccessful attempts to establish other exotic parasites are also discussed. Stemborer predators and diseases have been poorly studied in Mexico, and their potential as biocontrol agents is unknown. The current biological control programmes of stemborers in Mexico and the potential of indigenous and exotic parasites as biocontrol agents are discussed. National and international collaboration is stressed for optimisation of resources and efficient exchange of natural enemies and their mass rearing technology.

Mating Disruption of Mexican Rice Borers (Lepidoptera: Pyralidae) in Lower Rio Grande Valley Sugarcane

Mating disruption of Mexican rice borers, Eoreuma loftini (Dyar), by synthetic pheromone applications in sugarcane (Saccharum spp.) was investigated in large-scale field studies. Mating disruption was assessed using pheromone trapping, mating tables, stalk dissections, and nocturnal collections of adults. Pheromone traps were inappropriate for monitoring mating disruption. Mating tables supplied useful information but overestimated effects of pheromone applications on mating activities of feral rice borer populations. Adult collections and dissections supplied the least ambiguous assessment of mating activities, but were interpreted most easily in the presence of other substantiating data. Pheromone applications formulated in rubber ships or microporous beads and applied in a polybutene-based adhesive did not result in appreciable levels of mating disruption, and did not control rice borer populations or reduce associated stalk injury levels.

Susceptibility of Bermudagrass Cultivars to Eoreuma loftini (Lepidoptera: Pyralidae) in Subtropical Mexico

Susceptibility of eight bermudagrasses (Tifton 68, Tifton 78, Tifton 85, Gigante, Brazos, Cruza 1, Callie, and NK 37) to the Mexican rice borer, Eoreuma loftini (Dyar) was evaluated monthly during 1994 in northern Tamaulipas, northeastern Mexico. Damage by E. loftini occurred year around, peaking in April and December. Borer attack was reduced substantially after mowing the pastures to 3-5 cm height. Susceptibility of the cultivars to borer damage was influenced by stolon width, an important characteristic for E. loftini tunneling. This relationship between stolon width and borer damage was explained closely (R 2 = 0.86) by the curvilinear model y = (1.2 + 0.1757 x 3 ) 2, where y = borer damage and x = stolon diameter. The widest stemmed bermudagrass, and hence the most susceptible to E. loftini, was Tifton 68. Tunneling behavior of E. loftini, as affected by stem width of host plants, is discussed.

Suitability of Mexican Rice Borer (Lepidoptera: Pyralidae) as a Host for Pediobius furvus (Hymenoptera: Eulophidae)

The suitability of Mexican rice borer, Eoreuma loftini (Dyer) as a factitious (nonnatural) host for Pediobius furvus (Gahan) was examined. E. loftini was an acceptable and suitable host for oviposition and development by P. furvus. Both acceptability and suitability were affected by host pupal age. Host acceptability was initially relatively constant, declining rapidly when host pupae reached and surpassed 7 d of age. Suitability of young E. loftini pupae as a host for P. furvus was low (26.0 and 19.9% for 1- and 2-d-old pupae, respectively), increasing to 67.0% for 5-d-old pupae and then declining rapidly. Within-brood survival of parasitoid progeny was affected by both host age and weight with small, young pupae exhibiting lower within-brood survival (approximately 37%). Within-brood survival was highest in 5-d-old E. loftini pupae across all host weights. Progeny production per host increased with host weight. Prepupae of E. loftini were also suitable for parasitism but less so than pupae.