Blair V. Helson

Azadirachtin: An Effective Systemic Insecticide for Control of Agrilus planipennis (Coleoptera: Buprestidae)

ABSTRACT The emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), an invasive pest discovered in North America in 2002, is now well established and threatens ash (Fraxinus spp.) trees throughout the continent. Experiments were conducted to 1) examine the efficacy of an alternative natural pesticide, azadirachtin, to control emerald ash borer, and 2) determine foliar uptake and dissipation patterns after systemic injections of azadirachtin into trunks of small (2.2 cm diameter at breast height [dbh]), uninfested green ash trees. We found no evidence of mortality of adult beetles. In contrast, fewer larvae completed their development at dose levels ≥1.7 mg (AI)/cm dbh and development ceased beyond the second instar at dose levels ≤13.6 mg (AI)/cm dbh. Substantial concentrations (11.2 µg/g dry mass [SD = 7.55]) of azadirachtin were present in leaves within 7 d of treatment. After rapid initial uptake, concentrations in leaves declined logarithmically during the 55 d after injection. A similar pattern was observed in a separate experiment that examined the uptake and translocation of azadirachtin in larger green ash trees (22 cm dbh) treated with 250 mg (AI)/cm dbh with the EcoJect injection system. In another experiment, recently infested plantation green ash trees treated with doses ≥40 mg (AI)/cm dbh had significant reductions in adult emergence ≈1 yr postinjection. Given the inhibition of larval development, reduction of adult emergence, and the occurrence of foliar residues at biologically active concentrations, we conclude that azadirachtin is effective in protecting ash trees from emerald ash borer.

Ethyl m-digallate from red maple, Acer rubrum L., as the major resistance factor to forest tent caterpillar, Malacosoma disstria Hbn.

An ethanolic extract of red maple (Acer rubrum L.) leaves (RME) applied to trembling aspen (Populus tremuloides Michx.) leaves reduced feeding in choice test assays with forest tent caterpillar larvae (Malacosoma disstria Hbn.) (FTC), whereas a trembling aspen foliage extract, similarly applied, stimulated feeding. Compounds isolated from the RME were gallic acid, methyl gallate, ethyl gallate, m-digallate, ethyl m-digallate, 1-O-galloyl-β-D-glucose, 1-O-galloyl-α-L-rhamnose, kaempferol 3-O-β-D-glucoside, kaempferol 3-O-β-D-galactoside, kaempferol 3-O-β-L-rhamnoside, kaempferol-3-O-rhamnoglucoside, quercetin 3-O-β-D-glucoside, quercetin 3-O-β-L-rhamnoside and quercetin 3-O-rhamnoglucoside, (−)-epicatechin, (+)-catechin and ellagic acid. All of the gallates, (−)-epicatechin, and kaempferol 3-O-β-L-rhamnoside deterred feeding on trembling aspen leaf disks when applied at 0.28 mg/cm2. The two digallates deterred feeding by 90% and were the most effective. HPLC analysis indicated that ethyl m-digallate is present in amounts 10–100 × higher in RME (∼2.5–250 mg/g) than any other compound. Thus, ethyl m-digallate appears to be the major compound protecting red maple from feeding by FTC, with a minor contribution from other gallates.

Foliar residue dynamics of azadirachtins following direct stem injection into white and green ash trees for control of emerald ash borer

BACKGROUND Azadirachtins are natural insecticides derived from the neem tree. The emerald ash borer (EAB) is an exotic invasive insect pest that infests various ash tree species and has the potential for significant economic, aesthetic and ecological impacts throughout North America. The initial translocation and foliar residue dynamics of azadirachtins were examined following direct injection into white and green ash trees growing in urban scenarios as a potential control for EAB. RESULTS Substantial concentrations of azadirachtins A and B [mean maxima > 0.98 mg kg(-1) fresh weight (f.w.)] were observed within 2 days of injecting a specifically designed formulation of azadirachtins. Foliar residues declined exponentially through time, with half-life estimates ranging from 5.1 to 12.3 days. At the time of leaf senescence, foliar residue levels approximated 0.01 mg kg(-1) f.w., strongly mitigating the potential effects of non-target biota in soil or aquatic compartments. CONCLUSION The magnitude and duration of exposures observed in this field study were considered to be above the thresholds required for biological effectiveness against both larval and adult life stages of EAB. Results support the use of azadirachtins as an environmentally acceptable systemic insecticide for control of EAB and protection of high-value ash trees in urban environments.

Efficacy of Piper nigrum (Piperaceae) extract for control of insect defoliators of forest and ornamental trees

The acute toxicities of an extract obtained from a plant within the Piperaceae family and related synthetic analogues were tested against four common Canadian forest pest insects. The acute toxicity of the extract from black pepper, Piper nigrum L., was assessed after 1, 24, and 72 h by the percent larval mortality. The 24 h LC50 estimates for the P. nigrum extract were (in order of decreasing sensitivity) 0.012% for the introduced pine sawfly, Diprion similis (Hartig) (Hymenoptera: Diprionidae), 0.053% for the forest tent caterpillar, Malacosoma disstria Hubner (Lepidoptera: Lasiocampidae), 0.282% for the gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), and 0.998% for the spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Torticidae). There was no significant increase in mortality after 72 h. Seventy percent of L. dispar larvae dropped off or moved from branches within 1 h of application of 0.2% P. nigrum extract, indicating that these compounds have a repellent effect. Pipercide and nor-pipercide were more toxic to L. dispar and M. disstria larvae than piperolein A and a P. sarmentosum Roxb. amide 72 h after either oral or topical administration of these compounds. Toxic effects of piperamides were more pronounced by oral ingestion. Ninety percent mortality of L. dispar larvae occurred following an oral dose of 5 μg pipercide in diet, whereas mortality was only 40% following topical treatment at 5 μg pipercide/insect. Whole Piper extracts might be useful for the control of sawflies and tent caterpillars in small-scale applications, based on the demonstrated efficacy and reduced risk potential.

Efficacy of ultra-low volume aerial application of an azadirachtin-based insecticide for control of the pine false webworm, Acantholyda erythrocephala (L.) (Hymenoptera: Pamphiliidae), in Ontario, Canada

The efficacy of an aerial application at ultra-low volume of a 3% azadirachtin-based insecticide (Fortune AZA 3%) at a nominal application rate of 50 g azadirachtin ha−1 was evaluated for control of pine false webworm, Acantholyda erythrocephala (L.). Applications were made to three separate blocks in red pine plantations in south-central Ontario. Population indices of pine false webworm were compared between the treated blocks and three untreated blocks. Spray application was timed to coincide with the preponderance of egg hatch. Numbers of insects declined in all blocks between the adult emergence period and the subsequent larval generation, but decline in treated blocks was significantly greater. Reductions of arboreal stages (70-90% vs 5-50 %), frass drop estimates (0.10-0.13 vs 1.16-2.65 g/m2 d−1) and defoliation (10.5-15.5% vs 35-92.9%) all indicated significant differences in pine false webworm populations in treated as compared to untreated blocks. Mean deposits of azadirachtin A ranging from 0.44 to 1.47 wg g−1 in the canopy were well in excess of the 0.29 wg g−1 levels producing 91% mortality in laboratory bioassays. Azadirachtin-based insecticides provided good control of pine false webworm larvae in semi-mature and mature red pine plantations and would be suitable for use in an integrated control program for this insect.

Deposition of azadirachtin following ultra-low volume aerial applications to red pine plantations for control of pine false webworm, Acantholyda erythrocephala (L.) (Hymenoptera: Pamphiliidae), in Ontario, Canada

A completely randomized experimental design was employed to assess differences in on-target deposition of azadirachtin A following aerial applications of Fortune AZA 3% (50 g a.i. ha−1) to three red pine plantations infested with pine false webworm (Acantholyda erythrocephala (L.)). Substantial differences in mean foliar deposits were observed among plantations. However, these differences were not statistically significant owing to high variability in deposits within spray blocks. All mean deposits were well in excess of levels generating 91% mortality in laboratory bioassays against pine false webworm. In relation to a second objective, poor and occasionally insignificant correlation between deposits on natural foliage and two types of artificial collectors indicated that neither collector was effective in estimating true foliar deposition. Our results suggest that aerial applications of undiluted azadirachtin formulations at nominal rates of 50 g a.i. ha−1 yield foliar deposits in red pine canopies sufficient to induce high mortality in pine false webworm populations. Strict control over application parameters (track spacing, upwind offset and flight-line orientation) is necessary to minimize deposit variation.