Allen E. Knutson

Biology of Diorhabda elongata deserticola (Coleoptera: Chrysomelidae), an Asian leaf beetle for biological control of saltcedars (Tamarix spp.) in the United States

Adults and larvae of Diorhabda elongata Brullsubspecies deserticola Chen feed on the foliage of saltcedars (Tamarix spp.). All three instars are black, the 2nd with an indistinct, and the 3rd with a distinct yellowish lateral stripe; full-grown larvae reach ca. 9 mm in length and pupate in cells in litter on the ground or a few cm below the soil surface. Adults are yellowish with two dark brown stripes on each elytron. Duration of the egg averaged 5 days, 1st instar 4.9 days, 2nd instar 4.8 days, 3rd instar 7.4 days, prepupa 4.8 days, and pupa 7.1 days at 24.1C. Preoviposition averaged 3.9 days and an average female oviposited over a 12-day period and laid 194 eggs. Degree-day accumulations for development were 234.2 for the three larval instars and 91.3 for the pupa above a developmental threshold of 12.5C. Net reproductive rate (R0) in the laboratory at 28.6C and on the best Tamarix ac- cession was calculated at 88, generation time at 37 days, and innate capacity of increase (rm) at 0.112, giving a population doubling time of 6.2 days. In field cages in Colorado, Wyoming, Utah, Nevada, and California, overwintering adults emerged from late April to early May. Adults of the first generation emerged in early to mid-July, and 2nd generation adults emerged from mid-August to early September and overwintered. High populations of larvae developing in field cages caused defoliation, dieback, and sometimes death of the Tamarix trees. At the three study sites in Texas, maximum daylength was 14 h 21 min and larvae exposed to these conditions produced adults in reproductive diapause early in the season and subsequently failed to overwinter. North of 38 latitude in the United States, populations of D. e. deserticola originating from Fukang, China and Chilik, Kazakhstan are active throughout the growing season, successfully overwinter, and are potentially a highly effective control agent for saltcedar. Published by Elsevier Science (USA).

Virulence Analysis of Hessian Fly Populations From Texas, Oklahoma, and Kansas

ABSTRACT In recent years, the number of wheat, Triticum aestivum L., fields heavily infested by Hessian fly, Mayetiola destructor (Say), has increased in the Great Plains of the United States. Historically, resistance genes in wheat have been the most efficient means of controlling this insect pest. To determine which resistance genes are still effective in this area, virulence of six Hessian fly populations from Texas, Oklahoma, and Kansas was determined, using the resistance genes H3, H4, H5, H6, H7H8, H9, H10, H11, H12, H13, H16, H17, H18, H21, H22, H23, H24, H25, H26, H31, and Hdic. Five of the tested genes, H13, H21, H25, H26, and Hdic, conferred high levels of resistance (>80% of plants scored resistant) to all tested populations. Resistance levels for other genes varied depending on which Hessian fly population they were tested against. Biotype composition analysis of insects collected directly from wheat fields in Grayson County, TX, revealed that the proportion of individuals within this population virulent to the major resistance genes was highly variable (89% for H6, 58% for H9, 28% for H5, 22% for H26, 15% for H3, 9% for H18, 4% for H21, and 0% for H13). Results also revealed that the percentages of biotypes virulent to specific resistance genes in a given population are highly correlated (r2 = 0.97) with the percentages of susceptible plants in a virulence test. This suggests that virulence assays, which require less time and effort, can be used to approximate biotype composition.

A Degree-Day Model Initiated by Pheromone Trap Captures for Managing Pecan Nut Casebearer (Lepidoptera: Pyralidae) in Pecans

ABSTRACT Field observations from pecan, Carya illinoinensis (Wangenh.) Koch, orchards in Texas were used to develop and validate a degree-day model of cumulative proportional adult flight and oviposition and date of first observed nut entry by larvae of the first summer generation of the pecan nut casebearer, Acrobasis nuxvorella Nuenzig (Lepidoptera: Pyralidae). The model was initiated on the date of first sustained capture of adults in pheromone traps. Mean daily maximum and minimum temperatures were used to determine the sum of degree-days from onset to 99% moth flight and oviposition and the date on which first summer generation larvae were first observed penetrating pecan nuts. Cumulative proportional oviposition (y) was described by a modified Gompertz equation, y = 106.05 × exp(-(exp(3.11 - 0.00669 × (x - 1)))), with x = cumulative degree-days at a base temperature of 3.33°C. Cumulative proportional moth flight (y) was modeled as y = 102.62 × exp(-(exp(l.49 - 0.00571 × (x - 1)))). Model prediction error for dates of 10, 25, 50, 75, and 90% cumulative oviposition was 1.3 d and 83% of the predicted dates were within ± 2 d of the observed event. Prediction error for date of first observed nut entry was 2.2 d and 77% of model predictions were within ± 2 d of the observed event. The model provides ample lead time for producers to implement orchard scouting to assess pecan nut casebearer infestations and to apply an insecticide if needed to prevent economic loss.

Native Ant Responses to Solenopsis invicta Buren Reduction Using Broadcast Baits

Abstract A pilot study was conducted to investigate the impact of Solenopsis invicta management with an insect growth regulator bait (s-methoprene) on native ant species and to determine the responses of these species to S. invicta reduction. This invasive species alters the diversity and structure of different trophic levels of arthropod assemblages. Despite advances in S. invicta management using biological control agents, poison baits remain as the primary tool for effective fire ant management. However, the effect of these products on native ants is relatively unknown. Understanding these effects is critical to the development of S. invicta management strategies that include conservation of native ants. Native ants compete with S. invicta to some degree and can bolster efforts to release and establish exotic biological control agents to more effectively manage S. invicta. The study was carried out in Mumford, TX. Two treatments were used: a bait treatment that reduced S. invicta densities and a control. The treatments were randomly assigned to 1.33-ha blocks, replicated four times, and periodically inspected using complementary sampling techniques (pitfall traps, baited vials, manual collections, and nest surveys). Sixteen ant species were found among the two treatments. After S. invicta reduction, significant increases in densities of several other ant species were observed. Species within the assemblage shifted from the dominance by S. invicta to the dominance of the native pyramid ant, Dorymyrmex flavus McCook, which showed the most significant increase in bait treated blocks and was found to persist at densities significantly higher than the control for >2 yr after the last bait treatment. A temporary change in diversity was observed, indicating that use of a poison bait for S. invicta management benefited numerous resident species in the ant assemblage.

Establishment and Biological Success of Diorhabda elongata elongata1 on Invasive Tamarix in Texas

A leaf beetle, Diorhabda elongata elongata (Brullé), from Crete, Greece, was released unrestricted at two field locations (Lake Thomas and Beals Creek) within the upper Colorado River watershed of Texas between the summers of 2003 and 2004 as part of a Tamarix biological control program. D. elongata elongata released at the Lake Thomas site in August 2003 successfully overwintered and was recovered in the spring 2004; however, beetles were not recovered at Lake Thomas past June 2004 despite additional releases in July 2004. Following releases in April and July 2004 at Beals Creek, D. elongata elongata did establish and was subsequently recovered during 2005 and 2006. In August 2006, the D. elongata elongata population was dispersed throughout an area of approximately 12 hectares, beetles or larvae were present on 100% of the 47 trees surveyed and 57% of which (27 trees) were at least 90% defoliated by D. elongata elongata.

Tolerance to Feeding Damage by Cotton Fleahopper (Hemiptera: Miridae) Among Genotypes Representing Adapted Germplasm Pools of United States Upland Cotton

ABSTRACT Cotton fleahopper [Pseudatomoscelis seriatus (Reuter)] (Hemiptera: Miridae) is one of the most damaging insect pests of cotton (Gossypium hirsutum L.) in Texas and Oklahoma because of their feeding on small floral buds which are termed squares. Damage to early season squares can reduce yield, delay crop maturity and increase the risk of crop loss because of late season insect pests and adverse weather. Insecticide applications are the only control tactic. The objectives of this study were to determine the tolerance to cotton fleahopper injury to squares among upland cotton genotypes representing the adapted germplasm pools and breeding lines available to cotton breeders in the United States and to evaluate leaf hairiness as a resistant trait. Results of the choice and no-choice trials indicated that four entries, ‘Stoneville 474’, ‘Suregrow 747’, ‘Deltapine 50’, and ‘TAM 96WD-22 h’, were more tolerant to cotton fleahopper injury relative to the other 11 entries. In choice trials, cotton fleahopper density was significantly correlated with the density of trichomes on leaves, bracts and stems. However, there was no correlation between cotton fleahopper density and percent square damage in the choice trials, suggesting that in some genotypes the response to feeding injury is mediated by host plant resistance factors expressed as tolerance. Results of the no-choice studies also indicate that some genotypes express tolerance to cotton fleahopper feeding.

Resistance to seed feeding by southern green stink bug, Nezara viridula (Linnaeus), in soybean, Glycine max (L.) Merrill.

Abstract. Southern green stink bug, Nezara viridula (Linnnaeus), feeds on developing seeds of soybean, Glycine max (L.) Merrill, and is an important pest of the crop in the southern US. Sixteen soybean lines were evaluated for resistance by caging adult southern green stink bugs on pods in an insectary. The resistant standard, IAC-100, had the fewest feeding punctures per seed which was not significantly different from the number for genotypes V00-0742, V00-0842, or V99-1685. When exposed to southern green stink bug, the seed weight for IAC-100 was not significantly different from that of the genotypes PI 558040, V00-0870, or PI 588053A. The percentage of seed weight loss for IAC-100 was not significantly different from that of seed weight loss of PI 558040 or V00-0870 when exposed to feeding by southern green stink bug. The genotypes IAC-100, V00-0742, V00-0842, and V99-1685 are resistant to feeding by southern green stink bug based upon a reduction in feeding punctures, while genotypes IAC-100, PI 558040, and V00-0870 may provide a source of genetic traits for resistance by minimizing seed weight loss caused by feeding by southern green stink bug.

Effect of Red Imported Fire Ant, Solenopsis invicta1, on Abundance of Corn Earworm, Helicoverpa zea2, on Maize in Texas

Abstract Predator exclusion was used to measure the impact of the red imported fire ant, Solenopsis invicta Buren, on abundance of corn earworm, Helicoverpa zea (Boddie), eggs and larvae feeding on ears of maize, Zea mays L., and on corn earworm pupae in the soil in north-central Texas. Large field plots were treated with Amdro® Fire Ant Bait insecticide to selectively suppress fire ant abundance without impacting other arthropods or their behavior. Abundance of corn earworm eggs, larvae and pupae were determined in maize in which abundance of fire ants was significantly reduced and compared with the abundance of corn earworm life stages in maize with extant populations of fire ants. Fire ants had little or no measurable effect on abundance of corn earworm eggs or larvae on ears of maize in the three fields studied during two years. The mean total number of foraging fire ants and abundance of corn earworm pupae in the soil were significantly and negatively related. This result suggests that fire ants prey on pre-pupal corn earworm larvae as they crawl on the soil surface or prey on pupae in cells in the soil. The role of red imported fire ant as both a pest and beneficial in production of maize in central Texas is discussed.

Evaluation of sampling methods and development of sample plans for estimating predator densities in cotton.

Abstract The cost-reliability of five sampling methods (visual search, drop cloth, beat bucket, shake bucket, and sweep net) was determined for four groups of predatory arthropods on cotton plants in Texas. The beat bucket sample method was the most cost-reliable sampling method for Orius adults, and the beat bucket and drop cloth were the most cost-reliable methods for Orius nymphs. The drop cloth and beat bucket were the most cost-reliable methods for sampling spiders. For sampling adult Coccinellidae, the sweep net and the beat bucket were the most cost-reliable. The visual sample method was the least cost-reliable method for Orius adults and nymphs and spiders. No one sampling method was identified as the optimum method for all four predator groups. However, the relative cost-reliability of the beat bucket method ranked first or second among the five sampling methods and this method was chosen for further evaluation in field studies in Texas and Arizona. The relative cost-reliability of 1-, 3-, 5-, and 10-plants per beat bucket sample varied with predator group, but multiple plant sample units were equal to or more cost-reliable than the one plant sample unit. Fixed sample plans for the beat bucket method were developed for Orius adults, Orius nymphs, spiders, and adult Coccinellidae, and the sum of these groups using the 3-, 5-, and 10-plant sample unit sizes. The greater cost-reliability of the beat bucket sampling method and its ease of use is of particular advantage in assessing predator densities in a commercial cotton field monitoring program.

Field Evaluation of Diorhabda elongate and D. carinata (Coleoptera: Chrysomelidae) for Biological Control of Saltcedars (Tamarix spp.) in Northwest Texas

Abstract. Four species of Diorhabda (Coleoptera: Chrysomelidae) have been approved for release as biological control agents of invasive saltcedars (Tamarix spp.) in the U.S. Two species, D. elongata (Brullé) and D. carinata (Faldermann), were evaluated for their ability to establish populations in northwest Texas (from 32.5°N to 34.0°N) and increase in numbers sufficient to defoliate saltcedar trees. Following releases of adults during 2 years, D. elongata overwintered, established, and increased sufficiently to defoliate saltcedar trees at all three release sites. In contrast, D. carinata overwintered in the field at only one of three sites and then only in very low numbers. D. carinata did not defoliate saltcedar trees outside of cages at any release site. After 2 years of release efforts, D. carinata could not be detected at any of the three release sites during the third year and was not considered to have established. Survival of overwintering adult D. carinata was significantly greater than survival of overwintering D. elongata adults. However, D. carinata adults terminated overwintering quiescence earlier and were observed on saltcedar trees earlier in February and March than were D. elongata adults. These results suggested that emergence of adults from overwintering quiescence in late February and early March exposed D. carinata to freezing weather and contributed to the failure of the species to establish in northwest Texas. In contrast, D. elongata terminated overwintering quiescence latter and therefore experiences less risk of exposure to spring frost. These results suggested that D. elongata will be more effective than D. carinata for biological control of saltcedar in northwest Texas (32.5 to 34.0°N).