Nathan S. Little

Feeding Preference of Native Subterranean Termites (Isoptera: Rhinotermitidae: Reticulitermes) for Wood Containing Bark Beetle Pheromones and Blue-Stain Fungi

Surprisingly little research has been conducted to investigate interactions between subterranean termites and bark beetles. Facilitative interactions between these organisms could easily alter stand dynamics and impact wood utilization strategies. A series of American Wood Protection Association Standard E1-09 “choice tests” were carried out to determine the feeding preference of Reticulitermes flavipes Kollar (Isoptera: Rhinotermitidae) for blue-stained sapwood and sapwood impregnated with various bark beetle pheromones. Reticulitermes flavipes exhibited a feeding preference for both air-dried and kiln-dried blue-stained sapwood, unstained sapwood treated with frontalin, and air-dried blue-stained sapwood treated with a 0.02% solution of both frontalin and endo-brevicomin. The implications of these results are far reaching, with particular relevance to forest health, ecology, and utilization.

Termite-resistant heartwood. Effect of antioxidants on termite feeding deterrence and mortality

Abstract Biocides currently employed to prevent termite damage face environmental and toxicity concerns. We recently proposed that heartwood which is naturally resistant to termites might be due to the extractives having both toxicity and antioxidant properties and we reported that the artificial and benign antioxidant butylated hydroxytoluene (BHT) had termite feeding deterrence and toxicity properties. Here, we investigate other antioxidants, both natural and synthetic, and analogs which lack antioxidant properties, on Reticulitermes flavipes Kollar. Laboratory no-choice tests according to AWPA Standard E1 were performed. Antioxidants that are benign to humans had feeding deterrence and mortality properties to R. flavipes. Conversely, the non-antioxidant analogs, with the exception of the heterocyclic flavanone which was previously shown to be active against decay fungi, had little effect on R. flavipes. We conclude that R. flavipes avoids wood which contain high levels of antioxidants, such as heartwood with phenolic extractives.

Preference of Formosan Subterranean Termites for Blue-Stained Southern Yellow Pine Sapwood

ABSTRACT Little research has been conducted to investigate interactions between the invasive Formosan subterranean termite, Coptotermes formosanus Shiraki, and pine bark beetles native to the southeastern United States. Facilitative interactions between these organisms could alter stand dynamics and impact wood utilization strategies. American Wood Protection Association Standard El-09 choice tests were carried out to determine the feeding preference of Formosan subterranean termites for blue-stained versus unstained southern yellow pine sapwood. Three separate colonies of Formosan subterranean termites consumed on average twice as much air-dried blue-stained southern yellow pine sapwood over unstained air-dried controls. Additionally, Formosan subterranean termites consumed over five-times more kiln-dried blue-stained sapwood than unstained kiln-dried control wafers. The implications of these results are particularly relevant to pine forest ecology, nutrient cycling, and the utilization of blue-stained southern pine building products in the southeastern United States, where Formosan subterranean termites have become established.

Effect of different soils and pH amendments on brown-rot decay activity in a soil block test.

Abstract The soil block test is the most widely employed laboratory method for determination of biocide efficacy in North America. However, surprisingly little is known about the effect of different soil properties and soil amendments on fungal decay. Four soils with different textures and chemical properties were obtained and characterized. These soils, with and without pH amendments, were submitted to one soil block decay study using untreated southern pine wood and two brown-rot fungi. A second study examined the effect of adding water-soluble calcium chloride to soils, or directly to wood, on brown-rot decay. Based on the results of the first study with a limited number of soils, changes in the specified properties of the soil are suggested. Generally, fungal decay was reduced by raising the soil pH for acidic soils by hydrated lime as specified in the standards, or by adding water-soluble acidic calcium chloride to basic soils.

Supplemental Control with Diamides for Heliothines1 in Bt Cotton

Abstract. Supplemental control with diamides for bollworm, Helicoverpa zea (Boddie), in Bt cotton is becoming more frequent, but there is little information on net returns to growers. The value of spraying Bt cotton with commercially available diamides was evaluated at seven locations in the Mississippi Delta cropping region in 2014 and 2015. Plots of Bollgard II®, Widestrike 3®, and non-Bt cotton varieties planted at each location were divided into five subplots. Treatments randomly assigned to subplots of each cotton cultivar were: 1) lowest labeled rate of chlorantraniliprole applied at threshold, 2) lowest labeled rate of flubendiamide applied at threshold, 3) lowest labeled rate of λ-cyhalothrin + chlorantraniliprole applied at threshold, 4) sprayed check, which was the maximum labeled rate of chlorantraniliprole applied on a 3-week schedule and initiated before first bloom to minimize damage from heliothines, and 5) nontreated check. Each plot was monitored weekly for larval abundance and plant damage by examining 100 plants at random. Supplemental control applications were initiated when larval abundance (≥4 per 100 plants) and plant damage (>2% damaged bolls with larvae present) met economic thresholds outlined by the Mississippi State University Extension Service. Following first bloom, all non-target pests were controlled with broadcast sprays of insecticide with low or no known toxicity to heliothines. No differences were detected in yield among treatments for any given Bt cotton variety. In non-Bt cotton, all threshold treatments and the sprayed check yielded significantly more lint cotton per hectare than did nontreated plots. Mean larval numbers per 100 plants ranged from 0.75–5.95 in non-Bt cotton to 0.04–0.8 and 0.44–1.17 in Bollgard II and Widestrike 3 cottons, respectively. Non-Bt cotton required approximately one additional diamide application for heliothine control as compared to Bt cotton plots. Results indicated no economic benefit to supplemental spray of diamides for bollworms in Bt cotton at larval abundance observed during the study. Bt cotton alone seemed sufficient to control bollworms. This should provide confidence for producers to avoid overspray at near threshold densities of bollworms.

Effects of transgenic Bacillus thuringiensis cotton on insecticide use, heliothine counts, plant damage, and cotton yield: A meta-analysis, 1996-2015

The primary management tactic for lepidopteran pests of cotton in the United States of America (USA) is the use of transgenic cotton that produces Bacillus thuringiensis Berliner (Bt) toxins. The primary target pests of this technology are Helicoverpa zea (Boddie) and Heliothis virescens (F.) in the eastern and central Cotton Belt of the USA. Concerns over the evolution of resistance in H. zea to Bt toxins and scrutiny of the necessity of Bt crops has escalated. We reviewed published and unpublished data from field trials of Bt cotton in the eastern and central Cotton Belt of the USA through 2015 to evaluate the effectiveness of Bt cotton (Bollgard, Bollgard II, WideStrike, WideStrike 3, and TwinLink). Bt cotton reduced insecticide usage, reduced heliothine pest numbers and damage, and provided a yield benefit, but Bollgard II and WideStrike efficacy declined in the Midsouth over the period evaluated. In the Southeastern region, heliothine damage remained constant through 2015, but yield benefits declined from 2010 until 2015. Resistance of H. zea to several Bt toxins is the most plausible explanation for the observed changes in Bt cotton efficacy. The introduction of new Bt toxins such as found in Widestrike 3 and Twinlink may preserve the benefits of Bt crops. However, while both Widestrike 3 and Twinlink had less damage than Widestrike, damage levels of both were similar to Bollgard II.

Leaf Tissue Assay for Lepidopteran Pests of Bt Cotton

Abstract. Laboratory measurements of susceptibility to Bt toxins can be a poor indicator of the ability of an insect to survive on transgenic crops. We investigated the potential of using leaf tissue for evaluating heliothine susceptibilities to two dualgene Bt cottons, Gossypium hirsutum L. A preliminary study with different cotton leaf disk combinations was performed to determine the best procedure for using cotton tissue to assay bollworm, Helicoverpa zea Boddie, and tobacco budworm, Heliothis virescens F. Neonate larvae from a laboratory colony were assayed simultaneously on leaf disks of non-Bt and two dual-gene transgenic cottons in addition to meridic diet overlaid with discriminating doses of a commerciallyformulated Bt product. The bollworm colony in the laboratory was more tolerant than tobacco budworm to the commercially-formulated Bt product. When corrected for the non-Bt check, percentage of bollworm larval mortality was 42.1 and 71.9 on leaf disks of the two dual-gene Bt cottons. No tobacco budworm survived on dualgene Bt cotton leaf disks in the study. Assays using transgenic cotton leaf disks may compliment current meridic diet-based methods by providing a linkage to insect survival on Bt cotton plants.