Larval Threshold Research Articles

Evaluating foliar insecticides and economic thresholds for Tychius picirostris (Coleoptera: Curculionidae) management in Oregon white clover seed production.

The clover seed weevil, Tychius picirostris Fabricius (Coleoptera: Curculionidae), is a major pest in Oregon white clover seed crops. Reliance on synthetic pyrethroid insecticides and limited availability of diverse modes of action (MoAs) has increased insecticide resistance selection in regional T. picirostris populations, emphasizing the need to evaluate novel chemistries and rotational strategies for effective insecticide resistance management (IRM). The efficacy of 8 foliar insecticide formulations for managing T. picirostris adult and larval life stages was determined in small and large-plot field trials across 2 crop years. In both years, bifenthrin (Brigade 2EC), the grower's standard, showed negligible adult and larval suppression. Insecticide formulations with isocycloseram and cyantraniliprole active ingredients reduced adult and larval populations when applied at BBCH 59-60 (prebloom) and BBCH 65-66 (full bloom) growth stages, respectively. While differences in T. picirostris abundance were observed among insecticide treatments, seed yield differences were not detected in large-plot trials. Larval abundance was correlated with reduced seed yield, and an economic threshold of ≥3 larvae per 30 inflorescences was determined as a conservative larval threshold to justify foliar applications of diamide insecticides. Additional commercial white clover seed fields were surveyed to compare larval scouting techniques, including a standard Berlese funnel and a grower's do-it-yourself funnel. Both larval extraction techniques were correlated and provided similar estimates of larval abundance. These findings demonstrate new MoAs, optimal insecticide application timing, and larval monitoring methods that can be incorporated into an effective T. picirostris IRM program in white clover seed crops.

Derivation of Pheromone-Based Larval Thresholds in Spruce Budworm Accounting for Distance to Defoliated Forest Stands

Spruce budworm, Choristoneura fumiferana Clem. (Lepidoptera: Tortricidae), is the most severe defoliator of Pinaceae in Nearctic boreal forests. Three tools widely used to guide large-scale management decisions (year-to-year defoliation maps; density of overwintering second instars [L2]; number of males at pheromone traps) were integrated to derive pheromone-based thresholds corresponding to specific intergenerational transitions in larval densities (L2i → L2i+1), taking into account the novel finding that threshold estimates decline with distance to defoliated forest stands (DIST). Estimates of thresholds were highly variable between years, both numerically and in terms of interactive effects of L2i and DIST, which limit their heuristic value. In the context of early intervention strategy (L2i+1 > 6.5 individuals per branch), however, thresholds fluctuated within relatively narrow intervals across wide ranges of L2i and DIST, and values of 40-200 males per trap may thus be used as general guideline.

Evaluation of seed treatment insecticides for management of the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), in commercial rice fields in Louisiana

The rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), is the most injurious insect pest in US rice production. Yield losses in excess of 25% can occur from severe infestations. Management demonstrations were conducted in the 2008, 2009, 2010, and 2011 growing seasons to evaluate the use of commercially available insecticides to control L. oryzophilus in commercial rice fields. The demonstration tests, conducted on farms throughout Louisiana, compared the efficacies of recently registered seed treatment insecticides to untreated controls and to foliar applications of pyrethroids. Efficacy was assessed by collecting root/soil core samples three to four weeks after application of permanent flood and counting numbers of larvae and pupae in core samples. Tests were replicated across locations in multiple rice-producing Louisiana parishes. Densities of larvae and pupae in core samples exceeded the larval threshold (three larvae or pupae per core sample) in over 80% of untreated plots/cuts, confirming the ubiquity and severity of this insect as a pest of rice. Use of chlorantraniliprole (Dermacor® X-100, DuPont™ Crop Protection, Wilmington, DE), thiamethoxam (CruiserMaxx® Rice, Syngenta® Crop Protection, Greensboro, NC), and clothianidin (NipsIt Inside®, Valent® USA Corporation, Walnut Creek, CA) seed treatments significantly reduced L. oryzophilus infestation compared to untreated checks. Fewer larvae and pupae were observed in rice treated with chlorantraniliprole than in rice treated with other insecticides.

Biology and development of Laricobius kangdingensis Zilahi-Balogh and Jelínek, a newly discovered predator of Adelges tsugae

The biology and temperature-dependent development of Laricobius kangdingensis Zilahi-Balogh and Jelinek (Coleoptera: Derodontidae), a newly described predator of hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae) were investigated and compared with a related HWA predator, L. nigrinus Fender, that has already been released. As with other Laricobius species, there are four larval instars. The female to male sex ratio was 1:1.1. Mean lifetime fecundity per female was 196.4 eggs and 97.9 eggs for the parental generation (P1) and first filial generation (F1), respectively. Developmental rates at 6, 9, 12, 15, and 18°C were studied between fall 2002 and spring 2004 and used to determine low temperature development thresholds for the egg (2.8°C), and larval (1.6°C) stages. The egg and larval thresholds are lower than those observed for L. nigrinus. Laricobius kangdingensis individuals completed development only at 12 and 15°C; however, the adults did not emerge from aestivation after pupation. Our results suggest that L. kangdingensis may be a promising addition to the complex of predators currently being reared for control of HWA. Laricobius kangdingensis is long-lived, exhibits high fecundity, and can complete development on North American HWA. However, further studies will be necessary to secure its clearance for release, and the source of high mortality in the laboratory must be identified in order to improve its survival for mass-rearing.

Sensitivity Analysis of a Spatially-Explicit Stochastic Simulation Model of the Evolution of Resistance in Helicoverpa zea (Lepidoptera: Noctuidae) to Bt Transgenic Corn and Cotton

The sensitivities of a model simulating the evolution of resistance in Helicoverpa zea to Bt toxins in transgenic crops were investigated by examining effects of each of the model parameters on the frequency of resistance alleles after 8 yr. The functional dominance of resistance alleles and the initial frequency of those alleles had a major impact on resistance evolution. The survival of susceptible insects on the transgenic crops and the population dynamics of the insect, driven by winter survival and reproductive rates, were also important. In addition, agricultural practices including the proportion of the acreage planted to corn, and the larval threshold for spraying cotton fields affected the R-allele frequency. Many of these important parameters are inherently variable or cannot be measured with accuracy, so model output cannot be interpreted as being a forecast. However, this analysis is useful in focusing empirical research on those aspects of the insects' life system that have the largest effects on resistance development, and indicates ways in which to improve products and agricultural practices to increase the expected time to resistance. The model can thus be used as a scientific basis for devising a robust resistance management strategy for Bt crops.

Behavioural responses of larvae of Colorado potato beetle,Leptinotarsa decemlineata (Coleoptera: Chrysomelidae), to host plant volatile blends attractive to adults

Abstract Orientation of second‐ and fourth‐instar Colorado potato beetle (CPB) Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), to volatiles emitted from a solanaceous host, potato, and seven synthetic blends or three individual chemicals emitted by potato plants were investigated in laboratory bioassays. Both second‐ and fourth‐instar CPB were attracted to intact and mechanically damaged (MD) potato foliage. When offered a choice between intact and MD foliage, no preference was observed. Among seven synthetic blends tested (of which six are attractive to adult CPB), second‐ and fourth‐instar CPB were attracted only to a single three‐component blend comprising (±)‐linalool, methyl salicylate, and (Z)‐3‐hexenyl acetate. Individual compounds and two‐component blends were inactive. No significant difference was noted between larval responses to the attractive synthetic blend vs. MD potato foliage. Second‐and fourth‐instar larvae had similar thresholds for behaviour for the three‐component blend (50 µg source load). Female CPB were attracted to source loads 10× below the larval threshold (5 µg). Male CPB were the most sensitive life form tested with a behavioural threshold at 0.5 µg source load which was 10× and 100× below female and larval thresholds, respectively This is the first report of a synthetic chemical attractant for CPB larvae. As both larval and adult CPB are attracted to a single chemical blend, the usefulness of the attractant as a component of an attracticide or ‘push‐pull’ strategies for management of pestiferous populations is enhanced.

Evaluation of action thresholds and spinosad for lepidopteran pest management in Minnesota cabbage.

Action thresholds, based on the percentage of plants infested, for the lepidopteran pest complex in fresh-market cabbage Brassica oleracea variety capitata were evaluated in 1996 and 1997 in southern Minnesota. Three lepidopteran pests are common in Minnesota, including the imported cabbageworm, Pieris (=Artogeia) rapae (L.), diamondback moth, Plutella xylostella (L.), and the cabbage looper, Trichoplusia ni (Hübner). Most of the thresholds tested included all three pests. However, because T. ni is often the most consistent and damaging pest in Minnesota, two thresholds were based solely on the percentage of plants infested with T. ni eggs and larvae. Action thresholds were also evaluated for their compatibility with a recently labeled biologically based insecticide, spinosad, and a conventional pyrethroid, permethrin. Although all three lepidopteran pests were present in both years of the study, P. rapae provided most of the pest pressure in 1996, and T. ni was most abundant in 1997. Compared with the 0% larval infestation treatment (approximately weekly sprays from early heading to harvest), all action thresholds resulted in less insecticide use (17- 80%), while maintaining high levels of marketability. Despite variable pest pressure between years, one of the thresholds based solely on T. ni (10% of plants infested with eggs or larvae) performed as well as each of the thresholds based on all three species combined. For both years, and compared with a weekly spray schedule from early heading to harvest (average of 5.5 sprays per year), use of the 10% T. ni egg or larval threshold resulted in an average of 36.5% (3.5 sprays) and 65% (2.0 sprays) fewer applications of spinosad and permethrin, respectively, with no significant loss in marketability. The results indicate that a variety of incidence-based action thresholds can be used to ensure the production of high-quality cabbage in the midwestern United States with only minimal applications of spinosad or permethrin.

Evaluation of Chlorfenpyr for Dbm Control on Head Cabbage, 1996

Abstract The insecticides were evaluated at the Kula Research Station, Maui Agricultural Park, from April to May. The field was set up in a CRB design with eight treatments and four replications (blocks). Treatments were applied using a CO2 backpack sprayer set at 60 psi with an output of 100 GPA. One hollow cone nozzle (TX-26) was used per row. The first treatment was applied one week after transplanting into the field on 9 Apr. Subsequently, six applications were made weekly until the week before harvest on the following dates: 16, 23, 30 Apr, 7, 14, 21 May. The treated check treatment consisted of Bacillus thuringienis aizawai (BTA) or Proclaim applied using the University of Hawaii DBM resistance management protocol. BTA products are used prior to the cupping stage of growth. Proclaim 0.15 EC @ 6.0 oz./A is applied if DBM densities exceed 1.0 larva per plant. Proclaim is used after cupping if DBM densities exceed 0.5 larva/plant and 1-2 applications are made during the two weeks prior to harvest if DBM is present. Larval thresholds were determined by making larval counts on 10 plants/treatment replication. Mattch at 2.0 qt./acre was the BTA product used and it was applied on 16 and 23 Apr. Proclaim was applied on 30 Apr, 7 and 14 May.

Foliar Sprays Applied at Egg and Larval Thresholds to Control Boll Worms in Cotton, 1993

Abstract Cotton was planted on 24 May at the Eastern Shore Agricultural Experiment Station, Painter, VA. Row spacing was 36 inches, and Temik I5G (5 lb product/acre) was applied at planting for early-season Thrips control. Each plot consisted of a double 25 ft row, bordered on each side by an untreated guard row, and replicated 4 times in a RCBD. Sprays were applied using a single nozzle (TX-VS 4) boom delivering 10 gal water/acre at 60 psi. Egg threshold sprays were applied on 13 Aug when 10 or more BW eggs were found on 100 terminals. Larval threshold sprays were applied on 26 Aug when BW numbers reached or exceeded 3 live worms/100 bolls or squares. BW pressure was low to moderate. On 6 Sep, 25 random bolls were picked from each replicate of each treatment and examined for BW feeding damage.

Efficacy of Selected Insecticides Against Fall Armyworm, European Corn Borer and Boll Worm on Cotton in Southern North Carolina, 1993

Abstract Cotton was planted in a Wagram loamy sand on 10 May near Richlands, NC. The fertility and weed management programs followed NCSU recommendations with 0.6 lb (AI)/acre Temik 15G applied in furrow at planting. Plot size was 6 rows (38 inch centers) × 50 ft with 10 ft alleys. A RCBD was used with 4 replicates. Treatments were applied via a backpack-type CO2-pressurized sprayer calibrated to deliver 8 gal total volume per acre at 50 psi with a single TX-8 Spraying Systems® nozzle per row. Initial treatment was based upon exceeding a threshold of 10 eggs per 100 terminals, with the 2nd application 5 d later. The 3rd and 4th applications were triggered by meeting a larval threshold of 3 percent BW or FAW in fruit. Application dates were 22 and 27 Jul and 10 and 19 Aug. Twenty-five bolls per plot were inspected for live caterpillars and damage on 17 Aug and 15 Sep. Yields were picked with a 1 row John Deere mechanical harvester. Insect and yield data were subjected to ANOVA and DMRT.

Foliar Sprays for Bollworm Control in Cotton, 1992:

Abstract Cotton was planted on 21 May at the Eastern Shore Agricultural Experiment Station, Painter, VA. Plant spacing was 3-4 plants/ft with 36 inches between rows. Temik 15 G (0.75 lb [AI]/acre) was applied in the furrow at planting. Each plot consisted of a double 25 ft row bordered on each side by an untreated border row, replicated 4 times in a RCB design. Sprays were applied with a single (TXVS 4) hollow cone nozzle backpack sprayer delivering 10 gal H2O/acre at 60 psi. Evaluation criteria consisted of numbers of damaged fruiting forms (bolls and squares) from 25 randomly chosen fruiting forms/plot. Due to an unusually cool, wet summer, BW pressure was very low and late. Egg threshold was exceeded on 2 Sep (28 eggs/100 terminals), and Dipel 2 X (2 lb product/acre) and Larvin 3.2 EC (0.25 lb (Ai/acre) were applied on 3 Sep. A cool, rainy spell occurred the following week, resulting in low survival of the eggs. Larval threshold occurred on 11 Sep (3-4 BW/100 fruiting forms) and all treatments were applied on 14 Sep.

Efficacy of Selected Insecticides Against Fall Armyworm and Bollworm on Cotton in Southern North Carolina, 1992

Abstract Cotton was planted in a Wagram loamy sand on 28 Apr near Gibson, NC. The fertility and weed management programs followed NCSU recommendations with 0.6 lb (AI)/acre Temik 15 G applied in furrow at planting. Plot size was 6 rows (38 inch centers) x 50 ft with 10 ft alleys. A randomized complete block was used with 5 replicates. Treatments were applied via a backpack-type CO2-pressurized sprayer calibrated to deliver 8 gal total volume-per acre at 50 psi with a single TX-8 Spraying Systems® nozzle per row. Initial treatment was based upon exceeding a threshold of 10 eggs per 100 terminals, with the 2nd application 5 d later. The 3rd and final application was triggered by meeting a larval threshold of 3 percent BW or FAW in fruit. Application dates were 25 and 30 Jul and 21 Aug. Twenty-five squares and bolls per plot were inspected for live caterpillars and damage on 4 Aug and 3 Sep. Yields were picked with a 2 row John Deere mechanical harvester. Insect and yield data were subjected to ANOVA and DMRT (P = 0.05).

Foliar Sprays for Bollworm Control in Cotton, 1992:

Abstract Cotton was planted on 21 May at the Eastern Shore Agricultural Experiment Station, Painter, VA. Plant spacing was 3-4 plants/ft with 36 inches between rows. Temik 15 G (0.75 lb [AI]/acre) was applied in the furrow at planting. Each plot consisted of a double 25 ft row bordered on each side by an untreated border row, replicated 4 times in a RCB design. Sprays were applied with a single (TXVS 4) hollow cone nozzle backpack sprayer delivering 10 gal H2O/acre at 60 psi. Evaluation criteria consisted of numbers of damaged fruiting forms (bolls and squares) from 25 randomly chosen fruiting forms/plot. Due to an unusually cool, wet summer, BW pressure was very low and late. Egg threshold was exceeded on 2 Sep (28 eggs/100 terminals), and Dipel 2 X (2 lb product/acre) and Larvin 3.2 EC (0.25 lb (Ai/acre) were applied on 3 Sep. A cool, rainy spell occurred the following week, resulting in low survival of the eggs. Larval threshold occurred on 11 Sep (3-4 BW/100 fruiting forms) and all treatments were applied on 14 Sep.

Effect of Treatment Regimen on Control of Heliothis virescens and Helicoverpa zea (Lepidoptera: Noctuidae) on Cotton

Four foliar insecticide treatments ([All/ha), cypermethrin (0.067 kg), Bacillus thuringiensis subsp. kurstaki (Berliner) (29.6 billion International Units [BlUl), amitraz (0.14 kg), and B. thuringiensis + amitraz (29.6 BIU + 0.14 kg), were evaluated for influence on economic returns and for efficacy against the tobacco bud worm-boll worm complex, Heliothis virescens (F.) and Helicoverpa zea (Boddie), on cotton, Gossypium hirsutum L., at Florence, S.c., in 1988 and 1989. Each treatment was applied at regimens of scheduled applications (every 2-7 d, season-long), a threshold of five eggs per 100 plants, and a threshold of six larvae per 100 plants. Both years were characterized by low tobacco bud worm-boll worm population densities during June and early July followed by sharp increases in mid-July. Cotton flea hopper, Pseudatomoscelis seriatus (Reuter), densities did not exceed 1 per 10 plants. Cypermethrin and B. thuringiensis were the most effective and least effective treatments, respectively. Differences among treatment regimens for each insecticide usually were nonsignificant, but the efficacy of B. thuringiensis + amitraz was significantly reduced in 1988 when treatments were delayed until the larval threshold was reached. Economic returns were greater for the egg and larval thresholds than for the scheduled regimen. The low population densities of H. virescens, H. zea , and cotton flea hoppers before mid-July had no apparent effect on yields, and 15-17 season-long scheduled insecticide applications beginning in mid-June offered no advantage compared with five to eight applications (larval threshold) beginning in July.

On the Evolutionary Stability of Dispersal to Sink Habitats

On the Evolutionary Stability of Dispersal to Sink Habitats

Thermal Requirements for Embryonic and Larval Development of the Alfalfa Weevil in Wisconsin13

Embryonie and larval threshold temperatures for development of Hypera postica (Gyllenhal) were 10°C (50°F) and 8.9°C (48°F), respectively. Based on an average of 6 constant temperatures, 176 and 205 thermal units above 50°F were required to 1st and 50% hatch, respectively. Outdoors at Arlington, Wisconsin, 168 and 189 thermal units elapsed to 1st and 50% hatch. Averages of 70.6, 140.6, 207.0, and 297.9 thermal units accumulated outdoors above base 48°F for 50% development from eclosion through the 1st to 4th stadia (to prepupa), respectively.