Field Assessment of Aphid Doubling Time and Yield of Sorghum Susceptible and Partially Resistant to Sugarcane Aphid (Hemiptera: Aphididae).

Since outbreaks were first detected in grain sorghum, Sorghum bicolor (L.) Moench (Cyperales: Poaceae), in 2013, sugarcane aphid, Melanaphis sacchari Zehntner has become a major annual pest in grain sorghum-producing regions of North America. Economic thresholds have been recommended for susceptible hybrids, but these recommendations may not be suitable for grain sorghum hybrids partially resistant to sugarcane aphid. The objectives were to evaluate the grain yield-aphid density relationship and field-based population growth rates of the aphid on sorghum hybrids susceptible and partially resistant to sugarcane aphid across multiple years, locations, and hybrids. These data verified previously established economic injury levels for susceptible hybrids. The observed maximum aphid density ranged from 6 to 451 aphids per leaf for resistant hybrids and from 67 to 1,025 for susceptible hybrids. Across 50 location-year combinations, the maximum aphid density observed on resistant hybrids decreased by 0-99%, compared to a susceptible hybrid at the same location (mean reduction = 80%). Doubling time for sugarcane aphid populations on partially resistant hybrids was up to 6.4-fold higher than on known susceptible hybrids. For 48 of the 50 location-years, yield loss attributable to sugarcane aphid was not detected on the partially resistant hybrids; therefore, an economic injury level was unable to be estimated. If an economic injury level exists for resistant hybrids, it is likely at an aphid population level that exceeds the levels experienced in this study. It remains prudent to monitor resistant hybrids for unusual leaf decay associated with aphid densities that exceed current economic injury levels used for susceptible hybrids.

Evaluation of Tactics for Management of Sugarcane Aphid (Hemiptera: Aphididae) in Grain Sorghum.

The invasive sugarcane aphid, Melanaphis sacchari (Zehntner), is a devastating new pest of grain sorghum. Studies were conducted utilizing an integrated approach of four management tactics: planting date, insecticidal seed treatment, a foliar-applied insecticide, and plant resistance. Experiments were conducted in 2016 and 2017 at Griffin, Tifton, and Plains Georgia, and in 2016 in Texas, Alabama, and Oklahoma, United States. Early planting was effective in reducing damage and increasing yields when compared to the late planting. Use of a resistant variety reduced cumulative aphid-days, plant injury and usually prevented significant yield loss. Foliar application of flupyradifurone when aphids reached an economic threshold, was an effective management tactic preventing aphid injury and yield loss. Use of clothianidin seed treatment also reduced aphid injury and yield loss of the susceptible hybrid but generally did not prevent injury and yield loss of the resistant hybrid. We conclude that an earlier planting date coupled with a resistant variety and judicious use of an efficacious foliar-applied insecticide can effectively manage sugarcane aphid on grain sorghum. An insecticide seed treatment also may be useful to reduce the risk of sugarcane aphid damage to seedlings of susceptible hybrids.

Development of Economic Thresholds for Sugarcane Aphid (Hemiptera: Aphididae) in Susceptible Grain Sorghum Hybrids.

Sugarcane aphid, Melanaphis sacchari Zehtner (Hemiptera: Aphididae), outbreaks on grain sorghum were first detected in the United States in 2013. The spread of sugarcane aphid across the sorghum-producing regions of North America necessitated increased insecticide use to mitigate economic loss. A field experiment to develop economic thresholds for sugarcane aphid was conducted 15 times across seven locations across the southern United States during 3 yr (2014-2016). Grain sorghum hybrids were evaluated by measuring yield in response to a range of aphid infestations. Yield-aphid population density relationships were described by linear function, which facilitated calculating economic injury levels and economic thresholds. The slopes of the yield-aphid density regressions were significant, negative, and relatively stable across locations, years, and agronomic conditions. The relationships aggregated into two groups, populations that exhibited relatively slow and fast population growth, and common economic injury levels were determined using control costs and market values of grain. Average economic injury levels of 37 and 102 aphids per leaf were most applicable to the two groupings of sorghum/aphid relationships and aphid population growth. Using field-based sugarcane aphid population doubling time estimated from weekly observations of aphid densities, economic thresholds were calculated, ranging from 19 to 132 aphids per leaf across the 15 locations-years. Without site-specific knowledge of a slow-growing aphid population and given cost and market price variability of the system, a 40 aphid per leaf threshold is most prudent to use across the range of hybrid, environmental, and market conditions experienced in this study.

Oviposition Preference and Survival of the Mexican Rice Borer (Lepidoptera: Crambidae) in Bioenergy and Conventional Sugarcane and Sorghum.

Oviposition preference and host suitability of the Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), on bioenergy and conventional cultivars of sugarcane, Saccharum spp., and sorghum, Sorghum spp., were examined in a series of greenhouse experiments. Two energycane cultivars, two sugarcane cultivars, two high-biomass sorghum cultivars, and one sweet sorghum cultivar were assessed at two phenological stages (immature and mature). Mature plants possessed greater availability of dry leaf material compared with immature plants, and all E. loftini eggs were observed exclusively on dry leaves. Oviposition did not vary among host combinations (cultivar by phenological stage); however, eggs per plant and eggs per oviposition event were numerically greater on mature plants than immature plants. In a no-choice experiment, survival from egg to adult did not vary among host combinations, with <2.0% of E. loftini larvae surviving to adulthood. Failed establishment by neonates on plants was 13.4- to 53.9-fold greater than successful establishment across all host combinations. Results from this study suggest that plant physical characteristics continue to play an important role in host selection, but further evaluations will be needed to quantify other characteristics which influence host suitability.

Monitoring Mexican Rice Borer (Lepidoptera: Crambidae) Populations in Sugarcane and Rice With Conventional and Electronic Pheromone Traps.

The Mexican rice borer, Eoreuma loftini (Dyar), is a major pest of sugarcane, Saccharum spp., rice, Oryza sativa L., and other graminaceous crops in Texas and Louisiana. The ability of conventional and electronic pheromone traps to monitor E. loftini in sugarcane and rice habitats was evaluated in two separate 2-yr field studies. Bucket traps baited with a synthetic female sex pheromone monitored E. loftini populations in commercial sugarcane fields in Calcasieu and Jefferson Davis Parishes throughout the 2014 and 2015 growing seasons. The number of E. loftini captured differed among months, but not between years or parishes. The percentage of E. loftini-injured stalks was greater in 2015 than in 2014, peaking in September of both years. Daily trap capture was correlated with the percentage of injured stalks. Injury from E. loftini in Louisiana sugarcane remained relatively low (<3% bored internodes) in both 2014 and 2015. In a second experiment, electronic traps were compared with conventional pheromone traps for monitoring E. loftini populations in sugarcane and rice habitats in Texas in 2013 and 2015. Performance of earlier electronic trap prototypes in 2013 was inconsistent and less effective than conventional traps. Improved trap design in 2015 resulted in more than threefold greater moth capture in electronic traps than in conventional pheromone traps. Electronic traps demonstrated potential to improve monitoring strategies for this pest and should be evaluated for lepidopterous pests in a variety of cropping systems.

Sugarcane Aphid (Hemiptera: Aphididae): A New Pest on Sorghum in North America.

In 2013, the sugarcane aphid, Melanaphis sacchari (Zehntner) (Hemiptera: Aphididae), a new invasive pest of sorghum species in North America, was confirmed on sorghum in 4 states and 38 counties in the United States. In 2015, the aphid was reported on sorghum in 17 states and over 400 counties as well as all sorghum-producing regions in Mexico. Ability to overwinter on living annual and perennial hosts in southern sorghum-producing areas and wind-aided movement of alate aphids appear to be the main factors in its impressive geographic spread in North America. Morphological characteristics of the sugarcane aphid include dark tarsi, cornicles, and antennae, allowing easy differentiation from other aphids on the crop. Sugarcane aphid damages sorghum by removing sap and covering plants with honeydew, causing general plant decline and yield loss. Honeydew and sooty mold can disrupt harvesting. The aphid's high reproductive rate on susceptible sorghum hybrids has resulted in reports of yield loss ranging from 10% to greater than 50%. In response, a combination of research-based data and field observations has supported development of state extension identification, scouting, and treatment guides that aid in initiating insecticide applications to prevent yield losses. Highly efficacious insecticides have been identified and when complemented by weekly scouting and use of thresholds, economic loss by sugarcane aphid can be minimized. Some commercial sorghum hybrids are partially resistant to the aphid, and plant breeders have identified other lines with sugarcane aphid resistance. A very diverse community of predators and parasitoids of sugarcane aphid has been identified, and their value to limit sugarcane aphid population growth is under investigation.

Biology and Management of the Mexican Rice Borer (Lepidoptera: Crambidae) in Rice in the United States.

The Mexican rice borer, Eoreuma loftini (Dyar), is an invasive pest of rice, Oryza sativa L., in the Gulf Coast region of the United States. This pest also damages sugarcane, Saccharum spp. hybrids; corn, Zea mays L.; and sorghum, Sorghum bicolor (L.) Moench, and feeds on weedy noncrop grasses. Multiple aspects of integrated pest management including use of pheromone traps, manipulation of planting dates, harvest cutting height, stubble management, noncrop host management, soil fertility management, host plant resistance, use of insecticides, and biological control have been studied for Mexican rice borer management. However, the current management strategy in rice primarily relies on the use of chlorantraniliprole insecticide seed treatments. This profile addresses Mexican rice borer biology and management in rice in the United States.

El barrenador mexicano del arroz [Eoreuma loftini (Dyar)] es una plaga invasora de arroz (Oryza sativa L.) en la región de la Costa del Golfo de Estados Unidos. Esta plaga también afecta híbridos de caña de azúcar (Saccharum spp.), maíz (Zea mays L.), sorgo [Sorghum bicolor (L.) Moench), y se alimenta de malezas gramíneas. Múltiples aspectos del manejo integrado de plagas incluyendo el uso de trampas con feromonas, la manipulación de las fechas de siembra, la altura del corte durante la cosecha, el manejo de rastrojos, el manejo de hospederos alternos, el manejo de la fertilidad del suelo, la resistencia de la plantas, el uso de insecticidas y el control biológico han sido estudiados para el manejo del barrenador mexicano del arroz. Sin embargo, la estrategia de actual de manejo en arroz se basa principalmente en el tratamiento químico de la semilla con el uso del insecticida clorantraniliprol. Esta revisión se enfoca en la biología y manejo del barrenador mexicano del arroz en arroz en los Estados Unidos.

Yield Response to Mexican Rice Borer (Lepidoptera: Crambidae) Injury in Bioenergy and Conventional Sugarcane and Sorghum.

The Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae) is an invasive stem borer of sugarcane, Saccharum spp., and sorghum, Sorghum bicolor (L.), and poses a threat against the production of dedicated bioenergy feedstocks in the U.S. Gulf Coast region. A 2-yr field study was conducted in Jefferson County, TX, to evaluate yield losses associated with E. loftini feeding on bioenergy and conventional cultivars of sugarcane and sorghum under natural and artificially established E. loftini infestations. Bioenergy sugarcane (energycane) 'L 79-1002' and 'Ho 02-113' and sweet sorghum 'M81E' exhibited reduced E. loftini injury; however, these cultivars, along with high-biomass sorghum cultivar 'ES 5140', sustained greater losses in fresh stalk weight. Negative impacts to sucrose concentration from E. loftini injury were greatest in energycane, high-biomass sorghum, and sweet sorghum cultivars. Even under heavy E. loftini infestations, L 79-1002, Ho 02-113, and 'ES 5200' were estimated to produce more ethanol than all other cultivars under suppressed infestations. ES 5200, Ho 02-113, and L 79-1002 hold the greatest potential as dedicated bioenergy crops for production of ethanol in the Gulf Coast region; however, E. loftini management practices will need to be continued to mitigate yield losses.

Seasonal infestations of two stem borers (Lepidoptera: Crambidae) in noncrop grasses of Gulf Coast rice agroecosystems.

Infestations of two stem borers, Eoreuma loftini (Dyar) and Diatraea saccharalis (F.) (Lepidoptera: Crambidae), were compared in noncrop grasses adjacent to rice (Oryza sativa L.) fields. Three farms in the Texas rice Gulf Coast production area were surveyed every 6-8 wk between 2007 and 2009 using quadrat sampling along transects. Although D. saccharalis densities were relatively low, E. loftini average densities ranged from 0.3 to 5.7 immatures per m(2) throughout the 2-yr period. Early annual grasses including ryegrass, Lolium spp., and brome, Bromus spp., were infested during the spring, whereas the perennial johnsongrass, Sorghum halepense (L.) Pers., and Vasey's grass, Paspalum urvillei Steud., were infested throughout the year. Johnsongrass was the most prevalent host (41-78% relative abundance), but Vasey's grass (13-40% relative abundance) harbored as much as 62% of the recovered E. loftini immatures (during the winter). Young rice in newly planted fields did not host stem borers before June. April sampling in fallow rice fields showed that any available live grass material, volunteer rice or weed, can serve as a host during the spring. Our study suggests that noncrop grasses are year-round sources of E. loftini in Texas rice agroecosystems and may increase pest populations.

First Report of White Leaf Streak of Rice Caused by Mycovellosiella oryzae in Texas.

Rice (Oryza sativa L.) plants in experimental plots in Beaumont, TX developed symptoms on leaf blades similar to white leaf streak caused by Mycovellosiela oryzae (Deighton & Shaw) Deighton (synonym Ramularia oryzae Deighton & Shaw) (1,3,4) during the late summer of 2009. Symptoms were observed on several rice cultivars and breeding lines including Cocodrie, Cypress, and Lemont. Lesions usually appeared on lower leaves and were approximately 2 to 7 mm long and linear with whitish or grayish centers surrounded by a narrow brown-or-dark brown margin. Symptoms were similar to narrow brown leaf spot caused by Cercospora janseana (Racib.) O. Const. (synonym C. oryzae Miyake) (3,4), but the centers of lesions were slightly wider (up to 2 mm). Symptoms were visible on the upper and lower leaf surfaces. Some lesions on heavily infected leaves were long (10 to 15 × 0.5 to 2 mm) whitish streaks parallel to the midrib. Leaves with typical symptoms were collected and incubated in a petri dish lined with moistened filter paper for 3 to 4 days at room temperature under a 12-h fluorescent photoperiod. Conidiophores were produced on external mycelium growing out through stomata on the lesion surface. Conidiophores were hyaline, straight, and 7 to 22 µm long and 2 to 3 µm wide with conidial scars. Conidia were washed from the lesions, diluted in sterilized distilled water, and placed on acidified potato dextrose agar. After 6 to 7 days of incubation at room temperature, slow-growing colonies were transferred onto potato dextrose agar (PDA). Three isolates were obtained from single-spore cultures. The colonies of these isolates grew similarly and very slowly on PDA and their radial growth averaged 0.8 mm/day at room temperature. The colonies were dense, grayish, and did not produce any pigments. Conidia were formed singly or in chains and measured 12 to 30 µm long. They were hyaline, straight, cylindrical, typically with no or one septum, a few with two to three septa, and had a hilum and tapered ends. Pathogenicity of these three isolates was assessed in greenhouse tests by spraying a conidial suspension (105 conidia/ml) onto 12 plants of each of the cvs. Cocodrie, Cypress and Lemont at the late tillering stage. Inoculum was obtained by harvesting conidia from the colonies grown on PDA for 3 weeks at room temperature under a 12-h fluorescent photoperiod. Plants sprayed with sterilized distilled water served as the controls. All plants were maintained in a humid chamber for 2 days and then grown in a greenhouse at 20 to 31°C. After 15 days, early lesions appeared on inoculated leaf blades; after 4 weeks, typical symptoms similar to those observed in the field developed. Control plants did not exhibit any symptoms. M. oryzae was reisolated from symptomatic plants, confirming that the disease was caused by this pathogen. To our knowledge, this is the first report of white leaf streak on rice in Texas and the second report after Louisiana (2). This disease has been reported in Papua New Guinea, the Solomon Islands, North Borneo, Sierra Leone, and Nigeria (3,4). References: (1) F. C. Deighton and D. Shaw. Trans. Br. Mycol. Soc. 43:515, 1960. (2) A. K. M. Shahjahan et al. Plant Dis. 82:1282, 1998. (3) B. C. Sutton and A. K. M. Shahjahan. Nova Hedwigia 25:197, 1981. (4) R. K. Webster and P. S. Gunnell. Compendium of Rice Diseases. The American Phytopathological Society, St. Paul, MN, 1992.

Effect of planting date on Lissorhoptrus oryzophilus (Coleoptera: Curculionidae) density-yield relationship on rice in southeastern Texas.

Results of planting date and insecticide efficacy experiments targeting Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae) on rice, Oryza sativa L., in southeastern Texas between 2002 and 2007 were used to determine density-yield relationships as a function of planting date. Soil core samples were collected on two dates during main crop development to estimate immature L. oryzophilus populations followed by main and ratoon crop harvests. Analysis of covariance (ANCOVA) revealed that planting date did not affect the density-main crop yield relationship during most years and that these relationships varied substantially among years. For ratoon crop yield, an effect of main crop L. oryzophilus immature infestation was detected during some years, but the real effect of these populations on ratoon crop yield remains unclear. Using estimates of yield reduction per L. oryzophilus immature, economic injury levels were calculated. Main crop yields from treated plots and first soil core sample L. oryzophilus immature populations from untreated plots were significantly higher in plots planted at recommended dates than in plots planted earlier or later. This suggests that the presence of high populations of reproductive L. oryzophilus coincides with the period when rice fields planted at optimum dates are flooded. Results from this study reinforce the importance of managing L. oryzophilus populations when planting rice at recommended dates in southeastern Texas.

Attractiveness of stages of rice panicle development to Oebalus pugnax (Hemiptera: Pentatomidae).

Greenhouse experiments were conducted during 2004 and 2005 with male and female Oebalus pugnax (F.) (Hemiptera: Pentatomidae) caged on rice plants at different stages of panicle development with the objective of determining the most attractive stage to O. pugnax. Field-collected insects were released inside cages containing potted plants and observed during morning and afternoon hours for 5 d. Results showed that attractiveness of male and female O. pugnax to plants with panicles at milk and soft dough stages was greater than plants at preheading and heading stages. Preheading plants were the least attractive to the insects, confirming field observations. Results imply that insecticide applications during the preheading stage are likely ineffective and that monitoring efforts during the milk and soft dough stages of panicle development should be intensified.

Predicting economic losses from the continued spread of the Mexican rice borer (Lepidoptera: Crambidae).

The Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), is an invasive species that originated from Mexico, and it is threatening to cause major economic losses to sugarcane, Saccharum spp., and rice, Oryza sativa L., industries in Louisiana. The insect is expected to reach sugarcane and rice production areas in Louisiana by 2008, and infest all of Louisiana sugarcane and rice industries by 2035. When all sugarcane in Louisiana becomes infested, annual yield losses of $220 million would be expected for a cultivar of comparable susceptibility to LCP 85-384 (assuming this cultivar is planted on 100% of the production area). This also assumes the use of the current practice of rainfed production and one application of insecticide, which is presently used by farmers in Louisiana. Irrigation with 30 cm of water is predicted to reduce estimated losses by 29%, whereas four applications of a biorational insecticide such as tebufenozide are expected to reduce the loss in revenue by 53%. The use of the resistant 'HoCP 85-845' would reduce the projected loss in revenue by 24%. Combining all three management tactics on sugarcane, anticipated net loss in revenue would decrease by 66%. The rice industry in Louisiana is projected to suffer from a loss in revenue of $45 million when the entire state is infested. A 77% reduction in loss in revenue is expected with one application of lambda-cyhalothrin. A quarantine on east Texas sugarcane is estimated to save the Louisiana industry between $1.1 billion and $3.2 billion (depending on management) during the time needed for the insect to fully invade the state's sugarcane and rice producing area by natural migration rather than by accidental introduction. The rapid deployment of appropriate management tactics will have a key role in reducing the anticipated economic impact of E. loftini once it becomes a pest in Louisiana sugarcane and rice.

Determination of Oebalus pugnax (Hemiptera: Pentatomidae) spatial pattern in rice and development of visual sampling methods and population sampling plans.

Commercial rice, Oryza sativa L., fields in southeastern Texas were sampled during 2003 and 2004, and visual samples were compared with sweep net samples. Fields were sampled at different stages of panicle development, times of day, and by different operators. Significant differences were found between perimeter and within field sweep net samples, indicating that samples taken 9 m from the field margin overestimate within field Oebalus pugnax (F.) (Hemiptera: Pentatomidae) populations. Time of day did not significantly affect the number of O. pugnax caught with the sweep net; however, there was a trend to capture more insects during morning than afternoon. For all sampling methods evaluated during this study, O. pugnax was found to have an aggregated spatial pattern at most densities. When comparing sweep net with visual sampling methods, one sweep of the "long stick" and two sweeps of the "sweep stick" correlated well with the sweep net (r2 = 0.639 and r2 = 0.815, respectively). This relationship was not affected by time of day of sampling, stage of panicle development, type of planting or operator. Relative cost-reliability, which incorporates probability of adoption, indicates the visual methods are more cost-reliable than the sweep net for sampling O.

Most susceptible stage of rice panicle development to Oebalus pugnax (Hemiptera: Pentatomidae).

Oebalus pugnax (F.) (Hemiptera: Pentatomidae) damage to rice, Orya savita L., reduces rough and head rice yields, and grain quality. O. pugnax feeds on developing kernels, introducing pathogenic fungi and causing a discoloration of the grain known as "peck." The objective of this study was to determine the stage of rice panicle development most susceptible to O. pugnax attack. During 2005 and 2006, in greenhouse and field experiments, rice plants were caged at the boot stage and then infested with adult or nymphal O. pugnax. Plants were infested during one of three stages of panicle development: heading, milk, or soft dough. Insects were allowed to feed on the plants for the duration of each stage and then killed. After maturation, panicles were harvested, and grain was hulled and milled. Grain weight, percentage of pecky grain, and percentage of whole grain after milling were recorded. No differences were found in the weight of rough, brown, or milled rice infested with O. pugnax during different stages of panicle development. Number of filled grains per cage was not affected by O. pugnax, and number of empty grains per cage was affected in two of four experiments. Higher percentage of peck was found in grain from panicles infested during dough and milk than in grain from panicles infested during heading. Adult O. pugnax caused higher percentage of peck than nymphs in all stages of panicle development. An inverse relationship was found between percentage of peck and percentage of whole grain weight only in one of the experiments.

Role of oviposition preference in an invasive crambid impacting two graminaceous host crops.

Oviposition preference studies of the Mexican rice borer, Eoreuma loftini (Dyar), on sugarcane, Saccharum spp., and rice, Oryza sativa L., showed that drought stressed sugarcane was 1.8-fold more attractive based on egg masses/plant than well watered sugarcane. The E. loftini susceptible sugarcane cultivar LCP 85-384 was 1.6-fold more attractive than HoCP 85-845 based on numbers of eggs per egg mass. Egg masses were 9.2-fold more abundant and 2.3-fold larger on sugarcane than on rice. Rice, however, was preferred to sugarcane on a plant biomass basis. Oviposition on sugarcane occurred exclusively on dry leaf material, which increased under drought stress. Egg masses per plant increased on drought stressed sugarcane and were correlated with several foliar free amino acids essential for insect growth and development. The more resistant (based on injury) but more attractive (based on oviposition) rice cultivar XL8 had higher levels of several free amino acids than the susceptible cultivar Cocodrie. The association of host plant characteristics to oviposition preference is discussed. Projected oviposition patterns relative to sugarcane and rice production areas were estimated for Texas and Louisiana based on the availability of each host in different regions of each state. These results suggest that, where sugarcane and rice co-occur, the majority of eggs would be found on sugarcane early in the season, because of this crop's substantially greater biomass compared with rice. Abundance later in the season would also favor sugarcane; however, the abundance on rice would be greater than expected solely based on host availability, largely because of the greater preference per gram of rice plant dry weight.

Movement of Mexican rice borer (Lepidoptera: Crambidae) through the Texas rice belt.

Pheromone-baited traps were used to monitor the movement of the Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), through the Texas rice belt from 2000 to 2005. Based on location of discovery in each county and year, the average rate of spread from 1980 to 2005 was 23 km/yr. From 2000 to 2005, the leading edge of the infestation has moved 16.5 km/yr toward Louisiana. The 1.8-fold increase (99% confidence interval) of the area occupied from 2000 to 2005 in the Texas rice belt indicates an expansion of the distribution of E. loftini. If movement continues to occur at similar rates, E. loftini will reach Louisiana by 2008.

Rice water weevil females of different elytral color morphs: comparisons of locomotor activity, mating success, and reproductive capacity.

Females and males of the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Erirhinidae), have two elytral color morphs in Texas: the central pattern of their elytra is black (dark morph) or gray (light morph). In southeast Texas, the dark and light females exhibited similar proportions (28.6 and 32.0%, respectively) in populations collected during the spring. In this study, females of the two morphs were collected near rice fields in southeast Texas during April and May 2005. In the laboratory, light females were more active than dark ones. They mated equally successfully with males, irrespective of morph. For females supplied with males for 2 d or kept solitary, and then reared on rice seedlings for 48 d, no significant differences were found between the two morphs in oviposition period, number of eggs deposited, and survival rate. In both morphs, a proportion of mated females did not oviposit throughout the rearing period, implying that a mating experience might be necessary before reproductive development can be initiated. However, oviposition occurred in a proportion of females in which no mating experience could be detected, and their eggs produced larvae, which suggests the probability of existing parthenogenetic females in southeast Texas.

Resistance to stem borers (Lepidoptera: Crambidae) among Texas rice cultivars.

A 4-yr field study was conducted to assess the resistance of rice, Oryza sativa L., cultivars to injury from the sugarcane borer, Diatraea saccharalis (F.), and the Mexican rice borer, Eoreuma loftini (Dyar) (both Lepidoptera: Crambidae). Several cultivars showed reduced levels of injury ('CLXL8', 'XL8', 'Wells', 'Cheniere', and 'XP710' in 2003; CLXL8, XP723, Cheniere, and 'CL161' in 2004) and lower stem borer yield loss (CLXL8 in 2004) than the more susceptible 'Priscilla'. The resistant CLXL8 also had less injury and yield loss in 2004 and higher yield in 2003 than 'Cocodrie', currently the most popular rice cultivar in Texas and Louisiana. Linear regression analyses between whiteheads and main crop rice yield showed steeper negative slopes for the more resistant cultivars than the more susceptible cultivars, indicating a greater yield loss per whitehead on the resistant cultivars. Compensation from insect injury likely explains the positive associations established in our study between main crop yield and whiteheads for some cultivars. Cultivar resistance is anticipated to become a major control tactic in reducing infestations of E. loftini and D. saccharalis in the Texas and Louisiana rice industries.

Effects of nitrogen fertilizer applied before permanent flood on the interaction between rice and rice water weevil (Coleoptera: Curculionidae).

Nitrogen fertilizer was applied to rice, Oryza sativa L., before permanent flood to determine the interaction between rice and the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), through a series of experiments conducted over a 3-yr period in Texas and Louisiana. Both absolute and relative percentage of yield loss because of L. oryzophilus feeding was not affected by fertilizer rates in the Texas experiment. Absolute yield loss increased with nitrogen rates in 2001 and 2002 in the Louisiana experiment; however, percentage of yield loss was not affected. This finding suggests that nitrogen rate does not affect tolerance of rice to L. oryzophilus injury. In the Texas experiment, differences were detected for ratoon crop yield among nitrogen rates and insecticide that were applied at preflood on the main crop, indicating a carryover of fertilizer and insecticide effects from the main to the ratoon crop. L. oryzophilus populations tended to increase with nitrogen fertilizer in the Louisiana experiment. Our results show that farmers should not increase preflood nitrogen fertilizer to increase tolerance of rice to L. oryzophilus injury.