Evaluation of lectin-expressing transgenic sugarcane against stalkborers (Lepidoptera: Pyralidae): effects on life history parameters

The impact of snowdrop lectin (Galanthus nivalis agglutinin, GNA) expressed in transgenic sugarcane on life history parameters of Mexican rice borer [Eoreuma loftini (Dyar)] and sugarcane borer [Diatraea saccharalis (F.)] (both Lepidoptera: Pyralidae) was evaluated. In the laboratory, lyophilized sugarcane leaf sheath tissue was incorporated in a meridic diet resulting in a GNA concentration of 0.47% of total protein, and used for insect bioassays over two successive generations. Deleterious effects of GNA were not observed on survival, weight, and developmental periods of larvae and pupae, nor on adult fecundity and egg viability of D. saccharalis. Moreover, in the first generation, addition of transgenic sugarcane tissue to the diet enhanced larval growth in D. saccharalis resulting in higher larval and pupal weight compared with diet with nontransgenic sugarcane, but this effect was not observed in the second generation. In contrast, larval survival, percent adult emergence, and female fecundity of E. loftini were significantly reduced when fed transgenic sugarcane diet compared with nontransgenic sugarcane diet. In addition, a substantial reduction of female pupal weight of E. loftini was observed in the second generation. For both species, the only consistent effect of GNA in both generations was a reduction in adult female longevity. Life table parameters showed that GNA at the level found in the transgenic diet negatively affected development and reproduction of E. loftini, whereas it had a nil to positive effect on development and reproduction of D. saccharalis.     

Leptodictya tabida (Hemiptera: Tingidae): a potential threat to sugarcane production in Lower Rio Grande Valley of Texas

Areawide surveys and replicated cultivar trials were conducted in 2001 and 2002 in sugarcane (Saccharum spp.) fields in the Lower Rio Grande Valley of Texas to assess the distribution and incidence of the sugarcane tingid Leptodictya tabida (Herrich-Schaeffer). L. tabida was found in all fields surveyed during both years, infesting 60 and 68% of the plants, respectively. The average percentage of leaves infested was 11% in 2001 and 15% in 2002. In 2001, 'CP70-1133' was the most infested, 'CP72-1210' was the least infested, and intermediate infestation levels were evident in 'CP70-321' and 'TCP87-3388'. In 2002, however, TCP87-3388 and CP70-321 were more heavily infested, and CP71-1240 and CP71-1405 were the least infested. Mean densities of L. tabida recovered per plant varied between 1.2 bugs on CP72-1210 and 5.1 on CP70-1133 in 2001, and in 2002, from zero bugs on CP71-1240 and CP71-1405 to 5.3 on CP72-1210. In the cultivar trials, cultivar differences also were evident in both plant and leaf infestation levels, and the proportion of immatures to total L. tabida populations; 'HoCP91-555' had the lowest L. tabida infestations and 'NCo-310' had the greatest levels in both years. Although >5000 L. tabida from the field were collected and kept in the laboratory, no parasitoids were found. The distribution of the infestations during the surveys and in the field trial evaluations suggested that L. tabida populations have been spreading in sugarcane across the Lower Rio Grande Valley. Potential varietal resistance mechanisms are discussed.     

Laboratory evaluation of the virulence of Beauveria bassiana isolates to the sorghum shoot borer Chilo partellus Swinhoe (Lepidoptera: Pyralidae) and their characterization by RAPD-PCR

Beauveria bassiana has long been used as a mycopesticide. It has a wide host range; isolates have been reported to differ in host range and virulence to a given insect species. Identification of a molecular marker linked to a virulent phenotype to a target pest would be useful in screening for isolates effective against it. Twenty B. bassiana isolates were tested for their virulence to the second instar larvae of Chilo partellus Swinhoe in laboratory bioassays and their DNA fingerprints were generated by RAPD-PCR. Three arbitrary categories of aggressiveness were chosen; isolates that caused >70%, between 70 and 40% and <40% larval mortality were grouped as highly, medium and less aggressive types, respectively. In the random amplified polymorphic DNA (RAPD) analysis a 30% variability was observed among the isolates; which clustered into three major groups. The groups based on virulence rating did not match with the RAPD clusters. One of the highly aggressive isolates clustered with less aggressive isolates in one cluster and the other grouped along with the medium aggressive isolates in a different cluster. The B. bassiana isolates were classified phenotypically based on the taxonomic order of the original insect host and the climatic zone (tropical/temperate) from which they were isolated. No correlation between the aggressiveness of the isolate and the relatedness of the original insect host to the tested insect was observed; both the highly aggressive isolates were from coleopteran insects. A correlation was found between the RAPD grouping and the phenotypic classification of the isolates. All the lepidopteran isolates grouped into one major cluster, most sub clusters were constituted by isolates from the same climatic zone.     

Life history and life tables of Bactericera cockerelli (Hemiptera: Psyllidae) on potato under laboratory and field conditions in the lower Rio Grande Valley of Texas

Effective management of potato 'Zebra Chip' (ZC) disease caused by Cadidatus Liberibacter psyllaurous (syn. solanacearum) depends on the management of its insect vector insect, potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Psyllidae). To elucidate the age-specific population dynamics of B. cockerelli, the life-table parameters were determined on potato, Solanum tuberosum L., under both laboratory and field conditions in the Lower Rio Grande Valley (LRGV) of Texas. Generally, survival, fecundity, and longevity of B. cockerelli were significantly greater under laboratory than under field conditions. The mortality under laboratory conditions was mainly due to natural intrinsic mortality. However, under field conditions, most (83.2%) B. cockerelli were missing, and of those that were not, they developed slower, and had shorter preoviposition period, shorter oviposition period, shorter longevity, lower fecundity, and higher mortality than those under laboratory conditions. As a result, most of the life-table parameters of B. cockerelli, including the intrinsic rate of increase, finite rate of increase, and net reproductive rate, were significantly lower in the field under the environmental conditions of the LRGV of Texas than in the laboratory. The information could help increase our understanding of the epidemiology of the ZC diseases associated with the pathogens transmitted by this insect pest.     

Population dynamics of Bemisia argentifolii (Homoptera: Aleyrodidae) on spring collard and relationship to yield in the lower Rio Grande Valley of Texas

Seasonal population dynamics of the silverleaf whitefly, Bemisia argentifolii Bellows & Perring [formerly known as the sweetpotato whitefly, B. tabaci (Gennadius) Biotype "B"], was investigated on collard (Brassica oleracea L. variety acephala) during spring 1998 and 1999 in the Lower Rio Grande Valley of Texas. Yield loss caused by whitefly was determined by using insecticides to suppress whitefly populations to a low level. Although B. argentifolii populations of adults and immatures fluctuated greatly from April to June during the two seasons, the relative values were similar. Adult whiteflies first appeared on the plants in early April, increased rapidly within the month, peaked in May, and declined at the end of the season in early or mid-June. Whitefly eggs appeared on plants soon after adults were found, but high numbers of eggs were observed on foliage until late May 1998 and mid- and late May 1999. Nymphs and pupae increased slowly before June 1998 and increased early in May 1999. Whitefly population levels appeared to be positively associated with the availability and the growth of host plants until plant maturation, afterward being negatively related with plant quality in the late season. Temperature, rainfall, and natural enemies were not key factors in regulating population dynamics during the two seasons. Collard plants with heavy infestations of whiteflies were unmarketable because of the damage caused by honeydew and sooty mold on the foliage. Application of a combination of fenpropathrin (Danitol) and acephate (Orthene) not only significantly reduced the whitefly infestation levels but also reduced plant foliar damage, resulting in marketable foliage with six to seven times greater yield and higher quality compared with the untreated plants.     

Age-specific dose-mortality effects of Beauveria bassiana (Deuteromycotina: Hyphomycetes) on the European corn borer,Ostrinia nubilalis (Lepidoptera: Pyralidae)

Three isolates of Beauveria bassiana were evaluated under laboratory conditions for pathogenicity against the European corn borer, Ostrinia nubilalis. Dose-mortality regressions and nonparametric statistical analyses revealed significant differences in pathogenicity between isolates and across O. nubilalis instars. First instars were found to be the most susceptible of the five larval stages. Little difference was noted for instars 2, 3, and 5 within any of the three B. bassiana isolates. Fourth instar larvae were found to be the most tolerant in all cases.     

Laboratory and field evaluation of Beauveria bassiana bait against two cockroach species (Dictyoptera: Blattellidae,Blattidae) in Jinan City,East China

A Beauveria bassiana bait formulation was evaluated for its efficacy in the laboratory and field against German cockroaches, Blattella germanica (L.), and American cockroaches, Periplaneta americana (L.). The LT₅₀ values were 46 and 119?h, respectively, for B. germanica and P. americana. The cockroach species were lured and killed effectively when linear distance was about 5?m between B. bassiana bait and fresh mouse food. In the field, more than 90% relative decline in density was found 14?d after treatment, which lasted for 90?d. In conclusion, laboratory and field studies demonstrated the high efficacy of a B. bassiana bait formulation against common cockroach species.     

In vivo temperature-dependent development of Beauveria bassiana (Deuteromycotina: Hyphomycetes) mycosis of the European corn borer,Ostrinia nubilalis (Lepidoptera: Pyralidae)

The in vivo incubation period of Beauveria bassiana mycosis of the European corn borer, Ostrinia nubilalis, was found to vary in response to temperature of incubation, level of initial exposure (dose), and the age of the host larvae. Incubation temperature was found to be the dominant factor affecting disease development within each of the host instars examined, while dose produced significant effects only in the early instars. A nonlinear regression model was used to construct three-dimensional stimulus-response surfaces for each host instar. This model has provided reasonable predictions of the disease incubation period when used within the temperature regimes found throughout New York State.     

Laboratory evaluation of entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae against puparia and adults of Ceratitis capitata (Diptera: Tephritidae)

Laboratory experiments were done to measure the pathogenicity of 10 autochthonous isolates of Beauveria bassiana (Balsamo) Vuill. and of five Metarhizium anisopliae (Metsch.) Sorok. toward puparia and adults of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). Although all isolates applied via inoculation of the fungal suspensions on the ventral surface of the abdomen were pathogenic to adults, with mortality rates ranging from 30 to 100% and average survival times (ASTs) from 6.5 to 8.6 d, when C. capitata puparia were immersed in the conidial suspensions, only B. bassiana Bb-1333 and EABb 01/103-Su and M. anisopliae EAMa 01/58-Su isolates caused >50% mortality of puparia. In a second series of bioassays conducted on five selected isolates, adults were sprayed with four 10-fold concentrations ranging from 1.0 x 10(5) to 1.0 x 10(8) colony-forming units (cfu)/ml. The median lethal concentrations (LC50) of the four most virulent isolates ranged from 4.9 x 10(5) to 2.0 x 10(6) cfu/ml with estimated time to kill 50% of the insects ranging from 4.6 to 5.3 d. The effect of a sublethal dose (ca. LD50) of either B. bassiana EABb 01/103-Su or M. anisopliae EAMa 01/58-Su isolate was studied by reciprocal crossing. Treatment with B. bassiana reduced fecundity and fertility at 6, 8, and 10 d after treatment, with fecundity and fertility reductions ranging from 20.0 to 71.2% and from 33.6 to 60.0%, respectively. These reductions occurred in pairing combinations of treated females with either treated or nontreated males. M. anisopliae was more effective in reducing fecundity and fertility at 6 d after treatment, with the reduction varying from 58.4 to 72.1% and from 28.6 to 45.9%, respectively. In addition, the first oviposition was significantly delayed for 1 d in females treated by either fungal species. The above-mentioned five selected isolates were assayed against C. capitata puparia treated as late third instars in sterilized soil at 25'C under three moisture conditions (-0.1, -0.01, and -0.0055 MPa). At -0.01 MPa, all isolates were low pathogenic to C. capitata puparia, whereas significant differences in the puparia mortality occurred between isolates at -0.1 and -0.0055 MPa. The highest pupal mortalities ranged from 52.5 to 70.0%, as a function of soil moisture and were caused by EAMa 01/58-Su and Bb-1333 isolates.     

Effects of Elasmopalpus lignosellus (Lepidoptera: Pyralidae) damage on sugarcane yield

Feeding by lesser cornstalk borer, Elasmopalpus lignosellus (Zeller) (Lepidoptera: Pyralidae), larvae on sugarcane (a complex hybrid of Saccharum spp.) causes leaf damage, dead hearts, and dead plants that can result in stand and yield loss. A 2-yr greenhouse experiment was conducted to examine sugarcane variety and plant age-specific feeding responses to E. lignosellus. Plants growing from single-eye setts of three varieties were exposed to a single generation of E. lignosellus larvae beginning at the three-, five-, and seven-leaf stages. Results indicated that the physical damage and resulting yield loss of plants attacked by E. lignosellus larvae were dependent on the variety and leaf stage at which they were infested. Significantly more plant damage was observed in all three varieties when infested at the three- than at the seven-leaf stage. Larvae caused significantly more plant damage and reduced yield in CP 89-2143 than in CP 78-1628. Tiller production increased in CP78-1628 and CP 88-1762 when infested at the three-leaf stage, whereas tiller production, biomass and sugar yield decreased in CP 89-2143 when infested at all leaf stages, compared with the untreated control. There was no reduction in yield when CP 78-1628 was infested at the three- or five-leaf stages. Biomass was reduced in CP 88-1762 when plants were infested at any of the leaf stages, but sugar yield was reduced only when infested at the seven-leaf stage. These results indicate that compensation in response to E. lignosellus damage was variety dependent and declined with the delay in infestation time.     

Life table studies of Elasmopalpus lignosellus (Lepidoptera: Pyralidae) on sugarcane

The lesser cornstalk borer, Elasmopalpus lignosellus (Zeller) (Lepidoptera: Pyralidae) is an important pest of sugarcane (a complex hybrid of Saccharum spp.) in southern Florida. Reproductive and life table parameters for E. lignosellus were examined at nine constant temperatures from 13 to 36 °C with sugarcane as the larval food source. The pre- and postoviposition periods decreased with increasing temperatures and reached their minimums at 33 and 36 °C, respectively. The oviposition period was longest at 27 °C. The mean fecundity, stage-specific survival, stage-specific fecundity, intrinsic rate of increase, and finite rate of increase were greatest at 30 °C and decreased with increasing or decreasing temperature. The net reproductive rate was greatest at 27 °C. The Logan-6 model best described the relationship between temperature and intrinsic rate of increase. The generation and population doubling times were longest at 13 and shortest at 33 and 30 °C, respectively. The most favorable temperatures for E. lignosellus population growth were between 27 and 33°C. Life table parameters for E. lignosellus reared on sugarcane were greater than for the Mexican rice borer [Eoreuma loftini (Dyar) (Lepidoptera: Crambidae)] reared on an artificial diet at 30 °C. The intrinsic rates of increase for the sugarcane borer [Diatraea saccharalis (F.) (Lepidoptera: Crambidae)] reared on sugarcane or corn were the same as for E. lignosellus reared on sugarcane at 27 °C, but the net reproductive rate was four times higher for the former than the latter borer species.     

Simulated aerial sprays for field cage evaluation of Beauveria bassiana and Metarhizium brunneum (Ascomycetes: Hypocreales) against Anabrus simplex (Orthoptera: Tettigoniidae) in Montana

Field efficacy of the entomopathogenic Ascomycetes Beauveria bassiana strain GHA and Metarhizium brunneum strain F52 was evaluated against nymphs of the Mormon cricket, Anabrus simplex. Fungi were applied with a new apparatus that allows simulated aerial sprays to 0.1-m² areas in the field. The Mormon crickets were then individually housed in cylindrical, metal hardware cloth cages on treated grass. Both fungi demonstrated only marginal success in reducing immature Mormon cricket survival in the field cages. After 28 days, the field mortality of insects, corrected for control deaths, was 28 and 45% for B. bassiana and M. brunneum, respectively. Field-exposed but laboratory-incubated insects, however, suffered 90–100% mortality within 12 days with initial deaths occurring on Day 6 (Beauveria) or Day 5 (Metarhizium), indicating a lethal rate was applied and acquired by the crickets in the field. Potential daily body temperatures were determined for the entire post-treatment observation period using special thermal surrogates. High ambient temperatures and/or thermoregulation by Mormon crickets, in excess of the upper thermal limits of both fungi, prevented higher mortality from being expressed in the field. Thermal surrogates were used to develop models for predicting onset of mortality from infections. The surrogate data indicated mortality should begin between 8 and 26 days after treatment with M. brunneum and 11 and 33 days after treatment with B. bassiana. The timing of mortality in field cages was consistent with the upper boundaries of the temporal models developed from the thermal surrogates, i.e., at or after 28 days after treatment.     

Effect of exposure method to Beauveria bassiana and conidia concentration on mortality, mycosis, and sporulation in cadavers of Chilo partellus (Lepidoptera: Pyralidae)

The effects of exposure methods, conidial concentrations, and temperature on mortality, mycosis and sporulation in second instar Chilo partellus cadavers infected by Beauveria bassiana was investigated in laboratory studies. Larvae directly sprayed with conidia, exposed to conidia-treated leaves, and dipped into conidial suspension resulted in high mortality (98-100%). The longest LT50 (3.5 days) and days to mortality (2.6 days) were observed in the treated-leaves exposure method. The shortest LT50 (1 day) and days to mortality (1 day) were recorded for the dipping method. With increasing conidial concentrations, there were decreasing LT50 and days to mortality. Larvae exposed to treated leaves and larvae directly sprayed with conidial suspensions produced high mycoses in cadavers. Exposure of larvae to treated-leaves resulted in high sporulation. At lower concentrations of conidia, both mycosis and sporulation in cadavers were high. The optimum temperature for mycosis was 20 and 15 degrees C for sporulation.     

Reproductive potential of overwintering, F1, and F2 female boll weevils (Coleoptera: Curculionidae) in the Lower Rio Grande Valley of Texas

The feeding and oviposition activity of overwintering boll weevils, Anthonomus grandis grandis (Boheman), and seasonal fluctuations in development, survival, and reproduction of progeny of overwintering and first- and second-generation boll weevil females were determined in the laboratory at 27 degrees C, 65% RH, and a photoperiod of 12:12 (L:D) h. During the cotton-free period in the Lower Rio Grande Valley, female boll weevils without access to cotton resorb their unlaid eggs and enter reproductive diapause. However, when they were provided daily with greenhouse-grown cotton squares, commencement of oviposition began after 7, 15, or 20 d, depending on when they were captured. Females captured later in the winter fed longer before laying eggs than those captured in the early fall, suggesting that it may take females longer to terminate diapause the longer they have been dormant. The rate of feeding by females was significantly less during the winter months, and this may have affected the rate of diet-mediated termination of dormancy. Females of the first and second generations after the overwintering generation produced a significantly higher percentage of progeny surviving to adulthood and a higher proportion of these progeny were females. Offspring development time from overwintering female parents was significantly longer than that from first and second generations under the same laboratory conditions. The total number of lifetime eggs produced by females of the second generation during the cotton-growing season were approximately 9.9-fold higher than for overwintering females and 1.5-fold higher than for first-generation females. Life table calculations indicated that the population of second-generation boll weevils increased an average of 1.5-fold higher each generation than for females of the first generation and 22.6-fold higher than for overwintering females. Our data showed variation in boll weevil survival, development, and reproductive potential among the overwintering and first- and second-generation females, suggesting inherent seasonal fluctuations in these parameters.     

Beauveria bassiana yeast phase on agar medium and its pathogenicity against Diatraea saccharalis (Lepidoptera: Crambidae) and Tetranychus urticae (Acari: Tetranychidae)

Beauveria bassiana colonizes insect hosts initially through a yeast phase, which is common in some artificial liquid cultures, but not reported on artificial solid media. We describe a yeast-like phase for B. bassiana isolate 447 (ATCC 20872) on MacConkey agar and its virulence toward Diatraea saccharalis and Tetranychus urticae. The yeast-like cells of B. bassiana developed by budding from germinating conidia after 24-h incubation. Cells were typically 5-10 microm and fungal colonies were initially circular and mucoid, but later were covered with mycelia and conidia. Ability to produce yeast-like cells on MacConkey medium was relatively common among different B. bassiana isolates, but growth rate and timing of yeast-like cell production also varied. Metarhizium anisopliae and Paecilomyces spp. isolates did not grow as yeast-like cells on MacConkey medium. Yeast-like cells of B. bassiana 447 were more virulent against D. saccharalis than conidia when 10(7)cells/ml were used. At 10(8)cells/ml, the estimated mean survival time was 5.4 days for the yeast suspension and 7.7 days for the conidial suspension, perhaps due to faster germination. The LC(50) was also lower for yeast than conidial suspensions. Yeast-like cells and conidia had similar virulence against T. urticae; the average mortalities with yeast-like cells and conidia were, respectively, 42.8 and 45.0%, with 10(7)cells/ml, and 77.8 and 74.4%, with 10(8)cells/ml. The estimated mean survival times were 3.6 and 3.9 for yeast and conidial suspensions, respectively. The bioassay results demonstrate the yeast-like structures produced on MacConkey agar are effective as inoculum for B. bassiana applications against arthropod pests, and possibly superior to conidia against some species. Obtaining well-defined yeast phase cultures of entomopathogenic hyphomycetes may be an important step in studies of the biology and nutrition, pathogenesis, and the genetic manipulation of these fungi.     

Evaluation of Beauveria bassiana and Metarhizium anisopliae for Controlling Chilo partellus (Lepidoptera: Crambidae) in Maize

Maize (variety Katumani) was planted in a greenhouse and plants were infested with 20 Chilo partellus second instar larvae 3 and 4 weeks after plant emergence. One isolate of Beauveria bassiana (BB-01) and four isolates of Metarhizium anisopliae (PPRC-4, PPRC-19, PPRC-61 and EE-01) were sprayed onto the leaf whorl at 2×10⁸ conidia/mL 24 h after infestation. Leaf damage by the larvae was greatly reduced by the treatments. The mean daily temperature and relative humidity in the greenhouse ranged from 10 to 35°C and 30 to 90%, respectively. The growth of infested unsprayed plants was less than that of fungi treated plants. Stem tunneling (1-5%), deadheart (0-33%), number of attacked nodes (0.3-2.5) and holes (0.2-3.3) were also reduced in plants sprayed with conidial suspensions. Isolates PPRC-4, PPRC-19 and PPRC-61 seemed to be the best candidates for further development.