Clayton W. McCoy

Taxonomy of the acarine parasite Hirsutella thompsonii.

SUMMARY Cultural features and morphology of 11 isolates of the hyphomycete Hirsutella thompsonii, an important pathogen of various eriophyoid mites, are described and illustrated. Three morphologically distinct groups of H. thompsonii were distinguished and accordingly three varieties are proposed: H. thompsonii var. thompsonii, var. vinacea and var. synnematosa. The variety vinacea is characterized by vinaceous colonies and a different host, Acalitus vaccinii. The strains accommodated in the var. synnematosa were isolated from Eriophyes spp. and related genera. In fresh culture they produce cream-colored cylindrical synnemata, bearing two kinds of phialides: (1) single phialides with solitary conidia and (2) densely crowded phialides with catenulate conidia. In all three varieties two different conidiogenous structures are formed: (1) solitary often proliferating phialides producing one or more globose, verrucose conidia and (2) polyblastic conidiogenous cells with smooth-walled, subglobose to ellipsoidal conidia. Although H. thompsonii differs in some morphological characters from other species in the genus, its maintenance in Hirsutella is proposed.

Effect of fire ant (Solenopsis invicta) venom alkaloids on the in vitro germination and development of selected entomogenous fungi

Abstract Solenopsis invicta venom alkaloids were evaluated for antimycotic activity against Beauveria bassiana isolates, AF-4 and 447, Metarhizium anisopliae , and Paecilomyces fumosoroseus . Conidial germination of all isolates after 24 hr decreased with an increase in venom alkaloid concentration in both solid and liquid culture. Percentage germination of all isolates except P. fumosoroseus increased within 48 hr, indicating that the venom alkaloids act fungistatically on B. bassiana and M. anisopliae . Both P. fumosoroseus and M. anisopliae conidia were more sensitive to venom alkaloids than either of the B. bassiana isolates. P. fumosoroseus conidia were the most sensitive to venom alkaloids, since complete inhibition occurred at all concentrations >0.41 μg of alkaloid/cm 2 . B. bassiana (AF-4) was more tolerant to alkaloids than the 447 isolate with significantly higher ( P = 0.05) germination rates at 10, 20, and 30 μg of alkaloid/cm 2 . Vegetative growth of the B. bassiana isolates was also modified by the alkaloids in liquid culture. The hyphal body phase was induced at concentrations above 5 μg/cm 2 after 48 hr. No hyphal bodies were observed in media containing M. anisopliae or P. fumosoroseus at any alkaloid concentration.

Effects of Soil Type on Virulence and Persistence of Entomopathogenic Nematodes in Relation to Control of Diaprepes abbreviatus (Coleoptera: Curculionidae)

Abstract The Diaprepes root weevil Diaprepes abbreviatus (L.) is a major pest of citrus, ornamentals, and vegetables in Florida and the Caribbean. Entomopathogenic nematodes can provide substantial control of the root feeding larvae, but their efficacy can be affected by soil type. Our objective was to determine the effects of three soil types on the control of D. abbreviatus with Steinernema riobrave (Cabanillas Poinar & Raulston) and Heterorhabditis bacteriophora Poinar. In the laboratory we measured nematode virulence and persistence in a Marl, Ridge (entisol), and Flatwoods (spodosol) soil. The Marl soil contains a high silt and clay content (80 and 15%, respectively), whereas the other soils are >93% sand and typical soils of citrus production in Florida. The virulence of S. riobrave was greater than H. bacteriophora in all soils. Both nematode species exhibited greater virulence and persistence in Marl soil compared with sandy soils. Nematode virulence was greater in the spodosol than in the entisol soil. Oxygen levels (in the cups) were not significantly different among the soils. Further research is required to determine the cause of these trends and the applicability of these findings under different water tensions and under field conditions.

Conidiation of Hirsutella thompsonii var. synnematosa in submerged culture

Abstract Fourteen monosporal isolates of Hirsutella thompsonii grew vegetatively in various liquid media producing typical phialidic-like conidiophores. Hirsutella thompsonii var. synnematosa from Ivory Coast (HtIC) was the only pathotype which produced true conidia in submerged culture. HtIC began producing conidia after 3 days incubation reaching a peak ranging from 6.8 × 105 to 9.7 × 107 conidia/ml between 6 and 11 days. A concentration of 10 g/liter of corn steep liquor and 0.2% Tween 80 were essential for maximum conidiation. Submerged conidia had a smooth but somewhat rugose conidial walls, whereas aerially formed conidia were distinctly verrucose. Germination of submerged conidia ranged from 5.2 to 12.9% and were virulent causing 32.5% infection to adult citrus rust mites when sprayed on citrus foliage at 1.2 × 109 conidia/ml.

Comparison of beneficial traits among strains of the entomopathogenic nematode, Steinernema carpocapsae, for control of Curculio caryae (Coleoptera: Curculionidae)

Our objective was to compare beneficial traits among strains of Steinernema carpocapsae to identify or develop a superior biocontrol candidate for suppression of the pecan weevil, Curculio caryae. Virulence, environmental tolerance to heat and desiccation, and reproductive capacity were compared among eight strains. Fitness (in vitro growth) of the symbiotic bacteria, Xenorhabdus nematophila isolated from six of the nematode strains, was also compared. Significant differences were detected among nematode and bacteria strains for each trait. All nematode strains were more virulent to C. caryae adults than to larvae. No single S. carpocapsae strain was superior for all beneficial traits measured. Overall, Breton, DD136, Italian, and Kapow strains were ranked inferior to other strains. Agriotos, All, and Sal strains were superior when desiccation was a factor. When desiccation tolerance was removed as a factor, the Mexican strain also tended to fall into the superior rankings.

SEASONAL LIFE STAGE ABUNDANCE OF DIAPREPES ABBREVIATUS IN IRRIGATED AND NON-IRRIGATED CITRUS PLANTINGS IN CENTRAL FLORIDA

Abstract The seasonal abundance of various life stages of Diaprepes abbreviatus (L.), was monitored in separate years in adjacent irrigated and non-irrigated citrus plantings, as well as thickets of Brazilian-pepper located near Poinciana, FL in Osceola County. Adult emergence, estimated by weekly catches in cone-shaped ground traps, occurred throughout the year with a peak in mid-June in both citrus and Brazilian-pepper plantings. Onset of adult emergence coincided with an increase in soil moisture and temperature. Trap counts were highest when soil water potential increased to 3-5 centibars at a depth of 15-30 cm and soil temperature averaged 22-24EC. In the non-irrigated citrus planting, the adult emergence peak was of shorter duration, but of greater magnitude, compared to the irrigated planting. Although the alternate host, Brazilian-pepper, produced fewer weevils than did citrus, the seasonal emergence pattern was virtually the same. Adult abundance within the citrus plantings was also monitored weekly using modified Tedders traps. The number of adults captured approximated the number caught in ground traps. Adult number caught weekly changed seasonally, particularly in the fall when adult populations were the highest. Ground traps caught a larger number of adults in the spring. The number of egg masses collected weekly in the tree canopy and the number of neonates caught weekly beneath the tree canopy were both correlated with the number of adults captured weekly in modified Tedders traps. These data suggest that adults caught in modified Tedders traps provide a reliable indicator for estimating the seasonal abundance of all life stages within a citrus planting. Larvae of different instars, pupae, and teneral adults were recovered from the soil rhizosphere after periodic tree removal. No diseased or parasitized life stages were observed in the study. Most life stages were present in the soil at each sample date, but the proportion of larvae in various instars changed seasonally. The implications of this study for understanding the population dynamics of D. abbreviatus are discussed in relation to current and future IPM strategies.

Application and Evaluation of Entomopathogens for Citrus Pest Control

Originally from Southeast Asia, citrus has been introduced into many arid or humid, subtropical to tropical regions around the world where it is cultivated in a diverse array of quasi-permanent tree-crop plantings that range from small interplanted hillside patches to vast monocultural enterprises (Webber, 1948). Numerous arthropods infest citrus and some are considered serious pests locally or more globally either because of the direct damage they cause or because they transmit or otherwise facilitate important plant pathogens (e.g., the brown citrus aphid, Toxoptera citricida, vectors the citrus tristeza virus (CTV), Poprawski et al., 1999).

FIELD EFFICACY OF TWO COMMERCIAL PREPARATIONS OF ENTOMOPATHOGENIC NEMATODES AGAINST LARVAE OF DIAPREPES ABBREVIATUS (COLEOPTERA: CURCULIONIDAE) IN ALFISOL TYPE SOIL

Abstract Spring and fall field trials were conducted to determine the efficacy of two species of entomopathogenic nematodes for the control of larvae of Diaprepes abbreviatus in a citrus grove with alfisol type soil (sandy clay loam). Both Steinernema riobrave (Bio Vector 355) as a water-dispersible granule and Heterorhabditis indica (Grubstake™ 100) as a paste on sponge at rates from 22-108 IJ’s/cm2 failed to reduce larval populations in the tree rhizosphere at 25 d post-treatment. Larval parasitism by entomopathogenic nematodes in baited screen cages was sporadic over time, with the only significant treatment effect occurring at the highest rate (108 IJ’s/cm2) of S. riobrave in the fall at 7 d post-treatment. Possible constraints to nematode efficacy are discussed.

Estimating the Relative Abundance of Adult Citrus Root Weevils (Coleoptera: Curculionidae) with Modified Tedders Traps

Abstract Taylor’s power law (s2 = a x̄ b) was fitted to the means and variances of numbers of adult Diaprepes abbreviatus L. and Pachnaeus litus (Germar) caught monthly in modified Tedders traps (citrus Tedders traps). Data for D. abbreviatus were obtained in six Florida citrus groves, two located on the central ridge and the others in the central and southern flatwoods. Parameters for P. litus (a = 2.15, b = 1.17) using data pooled from two sites were consistent with parameters derived from the individual sites. Parameters derived from pooled data for D. abbreviatus were a = 2.69, b = 1.33; however, there was significant variability of the parameter b among sites. For specified levels of precision (confidence interval half-length:mean ratio), from 0–30% fewer traps were needed to estimate numbers of P. litus compared with D. abbreviatus at densities encountered in these groves. Plot size from 0.06 to >12 ha affected the numbers of traps needed to obtain monthly mean estimates of adult weevils per trap with a given level of precision. In general, sample precision was equal in large and small plots when population density in large plots was double that in small plots. At a given population density, ≈70% more traps were required in large compared with small plots to achieve a similar level of precision. Changes in trapped weevil abundance larger than 2.5-fold were detected as significantly different with the sampling plans used in these studies. Seasonality in the numbers of each species was evident at all sites (P = 0.05) because monthly means varied by 30- to 60-fold. In a separate study, the numbers of weevils recovered monthly from citrus Tedders traps were approximately congruent (r = 0.78, n = 33, P = 0.01) with numbers recovered from cone-shaped ground traps that only recover adult weevils as they emerge from soil. Annual maxima for both types of traps occurred at the same times during 33 mo, but each year weevil emergence from soil (as measured by cone traps) remained high for 1–2 mo after weevil recovery from citrus Tedders traps declined. Polynomial regression on monthly recovery from citrus Tedders traps explained 66% of the variation in monthly emergence of weevils from soil. Results of this study support the use of citrus Tedders traps in integrated pest management programs to detect the onset of emergence from soil by weevil cohorts, and to measure relative differences in weevil population density due to experimental treatments.

Isozyme differentiation among 17 geographical isolates of Hirsutella thompsonii

Abstract Electrophoretic analysis of mycelial preparations of 17 isolates of Hirsutella thompsonii demonstrated extensive variability in isozyme content. Many isolates possessed distinct electromorphs used to group or separate individual isolates. Coefficients of similarity based on isozyme patterns closely followed the morphological scheme used to separate H. thompsonii into three varieties. One exception, the nonsynnematous vinacious variety was very close to the nonsynnematous grayish-green variety biochemically. The electrophoretic data demonstrate that extensive differentiation among the H. thompsonii isolates is occurring at the subcellular level without attendant morphological changes.