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.     

Laboratory and field evaluations of the susceptibility of immature Choristoneura rosaceana (Lepidoptera: Tortricidae) to Beauveria bassiana (Hypocreales: Cordycipitaceae)

Abstract

The susceptibility of immature Choristoneura rosaceana (Harris) to Beauveria bassiana-GHA (BotaniGard® 22WP) was evaluated under laboratory and field conditions. Although egg masses ≤24 h old were susceptible to infection by topically sprayed B. bassiana spores in the laboratory and resulting mycosis significantly reduced the percent of neonates able to emerge, no significant egg mass infections resulted from orchard treatment of ≤24–48 h eggs. Exposure to high levels of the B. bassiana product on apple leaf surfaces in the laboratory caused significant dose-related mortality in first to fourth instar C. rosaceana. First instar C. rosaceana were the most susceptible of the larval stages assayed in the laboratory although only 36% of neonates introduced into the orchard prior to Beauveria treatment and 27% of the neonates emerging from orchard treated egg masses became infected. Fourth instar mortalities were similar but moderate when treated with 1×10⁸ spores mL^?1 in the orchard and on leaf surfaces in the laboratory. Beauveria bassiana-induced larval mortalities were significantly higher when the spores were applied directly to the larval integument as opposed to the leaf surface where the insect would encounter the pathogen in a treated orchard. Feeding of C. rosaceana larvae on antibiotic containing meridic diet prior to their use in trials did not impact the susceptibility of the larvae to B. bassiana. Antibiotic containing meridic diet significantly reduced larval C. rosaceana mortality when treated larvae or the spores were placed directly on the diet as opposed to leaf tissue.     

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.     

Laboratory and semi-field evaluation of Beauveria bassiana (Ascomycota: Hypocreales) against the lettuce aphid,Nasonovia ribisnigri (Hemiptera: Aphididae)

The lettuce aphid, Nasonovia ribisnigri (Mosley), is an economically important pest of lettuce worldwide. The entomopathogenic fungus Beauveria bassiana strain GHA has recently been reported as a potential biocontrol candidate for use against the lettuce aphid. This study provides information on the mortality inflicted by B. bassiana when applied against different life stages of the lettuce aphid under laboratory conditions and how fungus infection affects the aphid fecundity. In addition, temporal changes in persistence of fungus inoculum applied to foliage of young lettuce plants under semi-field conditions was analysed. Immature life stages were generally the least susceptible to fungal infection and the susceptibility of all stages was dose-dependent, with the highest mortality occurring at the highest dose. B. bassiana significantly affected the rate of nymph production by the lettuce aphid, with the highest effect seen when the alatoid fourth instar of N. ribisnigri was inoculated with B. bassiana. The persistence of B. bassiana conidia on lettuce foliage was not influenced by leaf position. Within 5 days, the cumulative percentage decline in the conidial population was 38% which declined further to 92% and 99% on day 11 and 20 post-spraying, respectively. In accordance, the infectivity to second instar lettuce aphid nymphs of B. bassiana conidia deposited on leaves declined according to an exponential decay model predicting an intercept of 0.59 ± 0.03 (S.E), a reduction in aphid mortality at a rate of 11% with each increasing day after fungal application and a fungus half-life of 6.34 ± 0.69 days.     

Role of cuticle-degrading enzymes of Beauveria bassiana and Metarhizium anisopliae in virulence on Plodia interpunctella (Lepidoptera,Pyralidae) larvae

Entomopathogenic fungi (EPF) are important biological control agents in pest management programs in agroecosystems against insect pests. EPF such as Beauveria bassiana (Bals.) Vuillemin and Metarhizium anisopliae (Metchn.) Sorokin produce a wide range of extracellular enzymes involved in disturbance of the first barrier in the insect cuticle comprising proteins, chitin, and lipids. Realizing relationships between the expression of these enzymes and fungal virulence might aid in development of effective mycoinsecticides. The virulence of B. bassiana (isolates TV and OZ1) and M. anisopliae (isolate CS1) were investigated on Plodia interpunctella (Hübner) larvae in this study. The third instar larvae were immersed in a suspension containing 1 × 10⁸ conidia mL^?1 of fungal conidial inoculum. The results revealed that all three fungal isolates caused mortality in larvae, but there was a considerable variation in their virulence. Total proteinase, exochitinase and lipase assays were done for these isolates. The TV isolate with the highest mortality with 41.7%, had the highest level of specific activity of exochitinase, protease, and lipase with 0.148, 0.654, and 0.190 U. mg^?1 protein, respectively. In the current study, a positive correlation was determined between the virulence of fungal isolates and the activities of protease and lipase, but this link was not significant for exochitinase. Our results demonstrated that extracellular enzymes, particularly protease and lipase, may play a crucial role in the virulence of these fungal isolates against P. interpunctella larvae.     

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.     

Efficacy of entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae against Thaumetopoea pityocampa Shiff. (Lepidoptera: Thaumatopoeidae)

Abstract

In this study, Metarhizium anisopliae TR 106 and Beauveria bassiana TR 217 was tested against fourth instar larvae of Thaumetopoea pityocampa. The LT₅₀ and LT₉₀ of 1?×?10⁶ concentration of M. anisopliae against T. pityocampa were 3.60 and 4.11 for direct application, while these were 2.87 and 3.60?days, respectively in leaves application. The LT₅₀ and LT₉₀ of the 1?×?10⁸ concentration of the same isolate were 2.50 and 2.95?days for direct application, and 2.98 and 3.74?days for leaves application. The LT₅₀ of insect and leaves application for 1?×?10⁶ of B. bassiana were 3.75 and 3.49?days, respectively. The LT₉₀ of same concentration for insect application was 4.48?days, while LT₉₀ for leaves application was 4.63?days. Similarly, LT₅₀ of insect and leaves application for 1?×?10⁸ of B. bassiana were 3.03 and 3.31?days, while LT₉₀ were 3.68 and 4.29?days, respectively. Approximate 100% mycosis was observed in all treatments.     

油松毛虫受球孢白僵菌感染的组织病理学变化

为了研究昆虫病原真菌对松毛虫的致病机理, 提供北方地区松毛虫生物防治的科学依据, 本研究采用球孢白僵菌Beauveria bassiana (Bals.) Vuillemin 菌株1573感染油松毛虫Dendrolimus tabulaeformis Tsai et Liu, 通过扫描电镜和石蜡切片光学显微镜观察技术, 研究了菌株的感染过程和虫体的组织病理学变化。结果表明, 该病原真菌通过穿透表皮入侵油松毛虫, 染菌后24 h, 观察到分生孢子附着于头部的颅顶, 单眼、触角和口器的基部, 在胸、腹部附着于毛簇、毛瘤、棘状突和节间褶。染菌后36 h, 孢子萌发长出菌丝, 在入侵部位, 菌丝的端部特化成附着胞和侵入钉。染菌后48 h, 菌丝依靠机械力和胞外酶的作用穿透表皮, 虫体表皮出现了裂痕和黑化。染菌后72 h, 菌丝已进入体腔, 感染血淋巴、脂肪体、肌肉、消化道、丝腺和神经组织, 并利用血液和内部组织器官作为营养大量繁殖, 此时, 虫体发涨, 表皮变暗。染菌后96 h, 菌丝占据了松毛虫的血腔, 内部的组织结构被完全瓦解, 松毛虫死亡。最后, 菌丝冲破体壁, 在尸体表面长出新的分生孢子。这些结果说明, 球孢白僵菌B. bassiana菌株1573是一种油松毛虫的高致病性菌株, 可以引起虫体的一系列组织病理变化而致其死亡。     

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.     

Hirsutella thompsonii a fungal parasite of the citrus rust mitePhyllocoptruta oleivora in the Rio Grande Valley of Texas

Hirsutella thompsonii, a hyphomycetous fungus, was found attacking the citrus rust mitePhyllocoptruta oleivora for the first time in May, 1972, in the Lower Rio Grande Valley of Texas. Sharp reductions in mite populations occurred during this period. The fungus was isolated from mites collected from citrus fruits and leaves. The parasitic nature and the distribution of the pathogen are described.