D. R. Ring

Degree-Day Models for Emergence and Development of the Rice Water Weevil (Coleoptera: Curculionidae) in Southwestern Louisiana

Abstract The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most destructive insect pest of rice in the United States. Degree-day (DD) models were developed to predict the emergence date of adult rice water weevils from overwintering in the spring and to describe larval and pupal development on two varieties of rice under field conditions. The model that best described emergence of weevils from overwintering was derived from 14 yr of light trap captures. The temperature threshold for the best-fit model was 15.6°C, the start date for the model (date at which degree-day accumulation begins) was 33 d after 1 January, and the end point for the model was a cumulative light trap capture of six weevils. By using these parameters, emergence of weevils occurred after accumulation of 139.2 DD (°C × day). The model predicted emergence of weevils in 2001, 2002, 2003, and 2004 with an error of 4, 7, 1, and 2 d, respectively. For the model describing larval development, the number of degree-days required for development from egg to 50% pupation was 359.1 ± 19.4 DD (°C × day) with a low temperature threshold of 10°C. The number of degree-days required for pupal development was 264.3 DD (°C × day), and the total degree-days required for development of one generation was ≈623.4 DD (°C × day). Larval development did not differ on cultivars ‘Jefferson’ and ‘Bengal’.

The influence of plant age on tolerance of rice to injury by the rice water weevil, Lissorhoptrus oryzophilus (Coleoptera: Curculionidae).

For most plant species, tolerance to many types of herbivory increases as plants age, but the applicability of this pattern to root herbivory has not been tested. Injury to roots of rice plants by larvae of the rice water weevil, Lissorhoptrus oryzophilus Kuschel, causes severe reductions in yields in the United States. It is generally thought that young rice plants, because their root systems are smaller, are less tolerant than older plants of root feeding by L. oryzophilus. Field experiments were conducted to test this hypothesis. Plots of rice (4.7 to 6.5 m2) were established and subjected to natural infestations of L. oryzophilus larvae. A soil insecticide was applied to plots at different times during the tillering phase of rice in order to manipulate the timing of weevil infestation. The impact of these treatments (timings of insecticide applications) was assessed by comparing relationships between yield loss and larval pressure for each treatment using analysis of covariance. Yield losses ranged from 13% to over 40% in plots not treated with insecticide. Patterns of yield losses from plots treated with insecticide at different times were best explained by the hypothesis that yield loss is determined both by the age of plants infested and by the size of larvae infesting plants. Young plants appear to be less tolerant than older plants, and feeding by large larvae appears to be more deleterious than feeding by smaller larvae. Management practices that delay infestation of rice by L. oryzophilus until plants are older may be an important component of management programmes for this pest.

The effects of four insecticides on the population dynamics of the rice water weevil, Lissorhoptrus oryzophilus Kuschel.

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, has been managed for the past 30 yrs using the soil insecticide carbofuran. The recent cancellation of the registration for carbofuran in rice has necessitated a shift to management strategies involving other insecticides, including lambda-cyhalothrin, fipronil, and diflubenzuron. Efficacies and effects on population dynamics of three alternatives to carbofuran (lambda-cyhalothrin and diflubenzuron as foliar sprays and fipronil as a seed treatment) were compared in two water-seeded and one drill-seeded field trials. Applications of lambda-cyhalothrin, but not of diflubenzuron or fipronil, resulted in decreases in the densities of rice water weevil adults and eggs. All three insecticides suppressed larval densities to levels comparable to, or lower than, densities in plots treated with carbofuran. All three alternatives to carbofuran differed from carbofuran with respect to their effects on the population dynamics of weevil larvae. Lambda-cyhalothri...

Sampling for the Sugarcane Borer (Lepidoptera: Crambidae) on Sugarcane in Louisiana

Abstract A 3-yr study was conducted in 0.6- to 2.0-ha sugarcane fields throughout south Louisiana under varying sugarcane borer, Diatraea saccharalis (F.), density levels to determine the spatial dispersion of infestations and to develop a sequential sampling plan. Infestations of D. saccharalis were randomly dispersed. Infestation levels (percentage of stalks infested) ranged from 0.6 to 33.3%. Frequency distributions of the number of infested stalks indicated that the Poisson distribution best fit the data. Tests of other distributions (negative binomial [aggregated], binomial [uniform], geometric, and hypergeometric) resulted in poorer fits. The sequential sampling plan devised, with lower and upper D. saccharalis infestation limits of 2 and 5% and 5 and 10%, required maximum average sample numbers of 7.1 and 5.5 (20-stalk samples), respectively, to make terminating management decisions. It is our assessment that implementation of these plans would decrease sampling effort by 50–60% when compared with sampling programs currently in use for D. saccharalis management decisions in Louisiana.

Feeding Behavior of Bollworm and Tobacco Budworm (Lepidoptera: Noctuidae) Larvae in Mixed Stands of Nontransgenic and Transgenic Cotton Expressing an Insecticidal Protein

Abstract Feeding behavior of third-instar bollworm, Helicoverpa zea (Boddie), and tobacco budworm, Heliothis virescens (F.), was observed in pure and mixed stands of nontransgenic and transgenic cotton (BTK), Gossypium hirsutum L., expressing an insecticidal protein CryIA(c) from a bacterium, Bacillus thuringiensis Berliner subsp. kurstaki. Five plant stands composed of BTK and non-BTK plants were evaluated; two pure stands and three mixed stands. Percentage ratios of BTK to non-BTK plants in the stands were 100:0, 75:25, 50:50, 25:75 and 0:100, respectively. In all stands with BTK plants, fewer bollworm and tobacco budworm larvae were found on BTK plants than non-BTK plants 24 h after infestation with third instars. At 48 h, significantly fewer tobacco budworm larvae, but not fewer bollworm larvae, were found on BTK plants. However, the number of larvae of either insect did not increase on non-BTK plants compared with the initial infestation density of three larvae per plant. The number of obacco budworm injured flower buds, and capsules was lower in all plant stands containing BTK plants compared with the pure stand of non-BTK at 48 h after infestation. Higher numbers of larvae on non-BTK plants were possibly the result of larval intoxication, reduced feeding, and increased plant abandonment and death on BTK plants rather than a classical feeding preference. Unexpectedly, the number of flower buds and capsules injured by bollworm and tobacco budworm when averaged per plant for all plants in a stand, differed little among the 75:25, 50:50 and 25:75 plant mixtures. These data suggest that larvae of both species frequently moved among plants, feeding indiscriminately on BTK and non-BTK plants.

Interactions of Metarhizium anisoplae and Tree-based Mulches in Repellence and Mycoses Against Coptotermes formosanus (Isoptera: Rhinotermitidae)

Abstract The use of mulch in urban landscapes has increased in the United States for the past decade. Tree-based organic mulches can supply Coptotermes formosanus Shiraki with food, moisture, and shelter. The current research contributes to mulch management technology in termite control. A choice test arena was designed to determine the repellence and mortality caused by commercial mulches treated with different concentrations of the fungus Metarhizium anisopliae (Metschnikoff) against C. formosanus. Each of six tree-based mulches (pine bark, pine straw, bald cypress, eucalyptus, water oak, and melaleuca) was coated with six conidial concentrations ranging from 1 × 103 to 1 × 108 conidia/ml. The foragers of C. formosanus were repelled significantly by the fungal-treated mulch substrates; the proportion of termites on fungal-treated mulch was usually <20% during the 28-d test. By day 28, >99% of the termites were killed in test arenas containing a chamber with mulch treated with 107 or 108 conidia/ml. M. anisopliae significantly reduced mulch consumption by 34–71%. Mulch consumption by the termites was negatively correlated with fungal concentration, and the type of mulch also affected consumption. The differences in termite foraging activities, mortality, and food consumption among mulches were usually confounded by differences in fungal concentrations of M. anisopliae. The results indicate that repellence and virulence of M. anisopliae conidia should significantly reduce the suitability of these six mulches as a habitat for C. formosanus.

Synergistic influence of halogenated flame retardants and nanoclay on flame performance of high density polyethylene and wood flour composites

High density polyethylene and wood flour (HDPE/WF) composites containing three flame modifiers (FMs) (i.e., two fire retardants: 1,2-bis(pentabromophenyl) and ethylene bis(tetrabromophthalimide), and one nanoclay), maleic anhydride grafted polyethylene (MAPE) and other processing aids were prepared through twin-screw extrusion, and their properties were characterized. The addition of FMs lowered the composite strength, but composite modulus did not change in a systematic manner. The fiber-polymer interfacial adhesion became increasingly deteriorated with the FM addition, and the use of MAPE coupling agent in the composites helped improve the interfacial adhesion. There was a synergistic effect of the fire retardants, nanoclay and MA-g-PE, especially for 1,2-bis(pentabromophenyl)–clay–MAPE system, on thermal stability and fire retardancy with lowered heat release rate and total heat release of the composites, leading to significantly improved flame performance.