Influence of <Emphasis Type="Italic">Lecanicillium attenuatum</Emphasis> on the development and reproduction of the cotton aphid, <Emphasis Type="Italic">Aphis gossypii</Emphasis>

The activity of entomopathogens on insect pests has been investigated for many species but the influence of entomopathogenic fungi on factors other than mortality relating to population increase has not been frequently studied. The influence of Lecanicillium attenuatum CS625 (=Verticillium lecanii CS625) on development and reproduction of cotton aphid (Aphis gossypii) was investigated. A conidia suspension of the isolate was applied onto first instar nymphs. Increased spore concentration did not significantly affect each nymphal stage, total nymphal period, pre-reproductive period and the age of first larviposition. A significant dose effect on reduction of life span, reproductive period and fecundity was observed in 1st and 3rd instars after spore application. When conidia were applied to 1st instars, life span was significantly reduced to 10.8 and 8.4 days at 1 × 10⁴ and 1 × 10⁸ conidia/ml, respectively from 12.2 days in the control. During the life span, total fecundity was 41 ± 7.3, 26 ± 0.8 and 22 ± 5.7 nymphs per female at 1 × 10⁴, 1 × 10⁶ and 1 × 10⁸ conidia/ml, respectively compared with 51 ± 2.0 nymphs per untreated female. Reproduction period was also significantly shortened with increasing spore concentration. Application of spores to 3rd instars showed a similar trend. However, daily fecundity of individual aphids was not affected by spore dose. It was concluded that the isolate of L. attenuatum is able to affect populations of cotton aphid by reducing life span and total fecundity as well as by killing the aphids directly.     

Evaluation of Lecanicillium longisporum, Vertalec for simultaneous suppression of cotton aphid, Aphis gossypii, and cucumber powdery mildew, Sphaerotheca fuliginea, on potted cucumbers

The commercial preparation of Lecanicillium longisporum, Vertalec^® was evaluated for simultaneous suppression of cotton aphid and cucumber powdery mildew on potted cucumber plants. Vertalec was applied onto cucumber plants that had been infested with either cotton aphid, spores of Sphaerotheca fuliginea or both. Irradiation-inactivated Vertalec (II Vertalec) was also applied to an identical series of cucumber plants as a control. The Vertalec was highly pathogenic against adult aphids with an LT₅₀ of 6.9 days. II Vertalec did not affect aphid survival. Application of either active or II Vertalec significantly suppressed spore production of S. fuliginea compared to the water control. For dual control assays, Vertalec applications were made one day after infestation of both aphid and S. fuliginea onto potted cucumbers. Fifteen days after the Vertalec treatments, the numbers of surviving aphids and the production of powdery mildew spores were significantly reduced compared with the water control. The presence of aphids also suppressed S. fuliginea spore production. Our results suggest the potential of a dual role for Vertalec as a microbial control agent of aphids and powdery mildew in cucumber.     

Verticillium lecanii Spore Formulation Using UV Protectant and Wetting Agent and the Biocontrol of Cotton Aphids

Verticillium lecanii spores (10⁸ spores ml⁻¹) suspended in 1% (w/v) montmorillonite SCPX-1374 and 1% (w/v) of the wetting agent, EM-APW#2, which is a polyoxyethylene, had approx. 80% survival after exposure to UV-C for 30 min and about 93% after exposure to UV-B for 6 h. In greenhouse testing, cotton aphid densities increased 14-fold over their initial density in 15 d without spore application. However, initial cotton aphid densities were decreased by 60% of the initial level when plants were treated with the spore formulation.     

Potential of Lecanicillium species for dual microbial control of aphids and the cucumber powdery mildew fungus, Sphaerotheca fuliginea

Detached leaf disc bioassays were conducted against cucumber powdery mildew and three species of aphid with three entomopathogenic species of Lecanicillium; Lecanicillium longisporum (Vertalec^®), Lecanicillium attenuatum (CS625), and an unidentified isolate (DAOM198499). The three Lecanicillium species had high virulence against the aphids Myzus persicae, Macrosiphum euphorbiae and Aulacorthum solani with the exception of DAOM 198499, which demonstrated reduced virulence to A. solani with an LT₅₀ of 6.4 days. Otherwise, LT₅₀ ranged between two and four days. Suspensions of conidia and blastospores of the Lecanicillium species were also applied onto 15 mm leaf discs dissected from cucumber plants previously inoculated with Sphaerotheca fuliginea. Powdery mildew did not develop when the Lecanicillium applications were made one and eight days after S. fuliginea inoculations. When Lecanicillium was applied to highly infected leaf discs 11 and 15 days after S. fuliginea inoculation, the application suppressed subsequent production of S. fuliginea spores as compared to the controls. These results suggest the potential of a dual role for Lecanicillium spp. as microbial control agents against aphids and powdery mildew.     

Abdominal gland secretion ofBledius rove beetles as an effective defence against predators

Recent investigations indicated thatBacillus thuringiensis delta-endotoxins (DET) possess aphidicidal activity in an artificial diet bioassay. Crystalline preparations of CryIIA, CryIIIA and CryIVD solubilized in a slightly alkaline sucrose/amino acid diet clearly imparted toxicity toward adults of potato aphid,Macrosiphum euphorbiae (Thomas) (Homoptera: Aphididae) after 4–5 days of continuous feeding. No obvious feeding deterrence was noted in these assays, as copious honeydew was produced and aphids often died in a feeding position. CryIIIA which was solubilized in aphid diet, but filtered to remove spores or crystalline toxin lacked aphidicidal activity. Spores from an acrystalliferous strain (EG2205) were not toxic by themselves at 7.75×10⁵ spores/ml aphid diet, but did restore toxicity to the filtered CryIIIA solution. Therefore, low levels of spores may be very effective in concert with DET for aphicidal activity. Results also clearly demonstrated that a suspension of crystalline CryIIIA alone, without spores, exhibited toxicity. Therefore, DET may be more toxic to the aphids when imbibed as a fine suspension, perhaps indicating the need for slow solubilization into the aphid midgut.     

The development and multiple uses of a standardised bioassay method to select hypocrealean fungi for biological control of aphids

A technically standardised bioassay method was designed, evaluated and used to assess virulence and host range of hypocrealean fungi against aphids. A track mounted sprayer was used to apply conidia because hand held versions of the same sprayer can be used for field applications, thereby allowing the outcome from laboratory experiments to predict activity in the field accurately. Eighteen fungal isolates were assessed in single concentration bioassays against the black bean aphid Aphis fabae Scopoli. Isolates comprised commercially available mycoinsecticides (based on Beauveria bassiana and Lecanicillium longisporum) and isolates of B. bassiana, Lecanicillium spp., Paecilomyces fumosoroseus and Metarhizium anisopliae. Aphid mortality was in excess of 80% for 15 isolates, and HRI 1.72 (L. longipsorum), Z11 (P. fumosoroseus), Mycotech strain GHA (B. bassiana) and ARSEF 2879 (B. bassiana) were studied further. Multiple concentration bioassays identified HRI 1.72 as the most virulent isolate against A. fabae with significantly smaller LC₅₀ and LT₅₀ values compared to other isolates. A precise LC₅₀ value (2.95 × 10² conidia ml⁻¹) was calculated for HRI 1.72 using a second multiple concentration assay with smaller concentrations of conidia. The four isolates were applied at a single concentration (1 × 10⁸ conidia ml⁻¹) against Myzus persicae, A. fabae, Acyrthosiphon pisum, Metopolophium dirhodum, Sitobion avenae and Rhopalosiphum padi. A ranking of aphid susceptibility was obtained, such that S. avenae > M. persicae, A. pisum, A. fabae > R. padi. Results indicate the importance of standardising bioassay methods to reduce bioassay variability without compromising the ability to use the bioassay to investigate fungus–host interactions under varying abiotic and biotic conditions.     

Pitfall trap catches of and aphid predation byPterostichus melanarius andPterostichus madidus in insecticide treated and untreated potatoes

Aphids were countedin situ and carabid beetle populations assessed by pitfall trapping betwen 1983–1985 in potato fields in Scotland treated with demeton-S-methyl (DSM) or untreated.Macrosiphum euphorbiae (Thomas) (Homoptera: Aphididae) was the most abundant aphid. Nineteen species of carabid beetles were trapped but the fauna was dominated byPterostichus melanarius (Ill.) andPterostichus madidus (Fabr.) (Coleoptera: Carabidae). Pitfall trap catches of these carabids were variable but generally lower in sprayed than unsprayed plots for a few days after DSM application and higher a week or two later. Of 1800P. melanarius and 910P. madidus dissected, 14.4 per cent and 30.5 per cent respectively, contained aphid remains. The proportion that had eaten aphids often was higher in sprayed than unsprayed plots immediately after treatment. In additional experiments, aphids treated with DSM fell from plants; four to five per cent of the theoretically applied dose of DSM reached the ground in a closed-canopy potato crop; and no mortality occurred whenPterostichus spp. were exposed to DSM in a field bioassay. It is proposed that observed patterns in trap catch ofPterostichus spp. around times of pesticide application may be due in part to aphids falling to the ground after treatment. Beetles that eat these fallen aphids may be less hungry, less active and less likely to be trapped. Later increases in catches may be attributed to hungry, more active beetles, a consequence of prey removal by the insecticide. Although this hypothesis requires further research, it is clear that the effects of insecticide treatment on carabid populations cannot be measured by pitfall trapping alone.     

Virulence of Hypocreales fungi to pecan aphids (Hemiptera: Aphididae) in the laboratory

There is need for efficacious biocontrol agents for aphids in commercial orchards. As a preliminary step to this end we determined the virulence of several Hypocreales fungi to pecan aphids. In the first experiment we tested the virulence of Isaria fumosorosea (ARSEF 3581) blastospores to three pecan aphids Monellia caryella, Melanocallis caryaefoliae, and Monelliopsis pecanis under laboratory conditions. Rates of 1 × 10⁷ or 1 × 10⁸ spores per ml were applied in 2 ml via a spray tower to 90 mm Petri dishes containing 10 aphids each. Mortality and mycosis were determined after 24, 48 and 72 h. Treatment effects were observed by 48 h post-application, and by 72 h the higher application rate caused >90% mortality and mycosis in M. caryella and M. caryaefoliae, whereas <70% was observed in M. pecanis.We conducted two subsequent experiments (Experiments 2 and 3), using the same methodology, to compare the virulence of several Hypocreales species and strains against the aphid of primary economic concern to most pecan growers, M. caryaefoliae. In Experiment 2, we compared blastospores and conidia of two I. fumosorosea strains (ARSEF 3581 and ATCC 20874 [= strain 97]). The blastospores of ARSEF 3581 and conidia of ATCC 20874 showed higher virulence than other treatments and thus were included in Experiment 3, which also compared the virulence of conidia of Beauveria bassiana (GHA strain) and Metarhizium anisopliae (F52 strain). Results in Experiment 3 indicated the highest virulence in I. fumosorosea 3581 blastospores and M. anisopliae (F52) followed by I. fumosorosea (20874) conidia. The detection of pathogenicity to pecan aphids establishes the potential for commercial usage and additional study. Results reported here will narrow treatments to test in future greenhouse and field trials.     

Oviposition avoidance of parasitized aphid colonies by the syrphid predator Episyrphus balteatus mediated by different cues

Oviposition decisions made by members of a guild of natural enemies can have evolved to avoid intraguild predation, potentially avoiding the disruption of the extraguild prey control. We have studied the oviposition preference of the aphidophagous predator Episyrphus balteatus De Geer (Diptera: Syrphidae) within colonies of Myzus persicae Sulzer (Hemiptera: Aphididae) in the presence of two developmental stages of the aphid parasitoid Aphidius colemani Viereck (Hymenoptera: Aphidiidae). Results from a greenhouse choice experiment showed that E. balteatus females lay significantly fewer eggs in colonies with mummified aphids than in unparasitized colonies. Colonies of parasitized, but not yet mummified did not contain significantly fewer eggs than colonies with unparasitized aphids. In three no-choice experiments, we assessed stimuli coming from aphid honeydew, from the aphids themselves and also from extracts of the aphid bodies, and all of these stimuli mediate the discrimination of mummified aphids from healthy aphids. To a lesser extent these stimuli also contribute to the discrimination against aphids that are parasitized but not yet mummified. These results suggest that the effects of these two species could be complementary for the control of M. persicae, since the species that acts as an intraguild predator, E. balteatus, avoids ovipositing on aphid colonies parasitized by the intraguild prey, A. colemani.     

The effect of introducing the aphid-pathogenic fungus Erynia neoaphidis into populations of cereal aphids

The aphid-pathogenic fungus Erynia neoaphidis, as dried fungus-infected aphids, was applied to caged plots of winter wheat infested with cereal aphids at two sites, one in Hertfordshire and the other in Hampshire, in 1983. In each trial, the fungus became established in the aphid populations in the treated plots even though conditions were drier than average and therefore sub-optimal for fungus spread. Treatment applied in the third week of June increased the proportion of infected aphids more than that applied two weeks later at one site, and the early application was the only treatment to have an obvious effect at the other. In spite of the observed effect of treatments on the proportion of infected aphids, the fungus failed to reduce the numbers of aphids relative to those in untreated plots, chiefly because in these plots many aphids were killed by fungi of the same species as that introduced and other related species from natural sources. Artificial introduction of E. neoaphidis acts too slowly and unpredictably to be likely to form a practical alternative to conventional insecticides for cereal aphid control.     

紫外长期胁迫对高世代麦长管蚜生命表参数的影响

为了评估紫外连续处理对第20代以后麦长管蚜Sitobion avenae (Fabricius)种群动态的影响,采用特定年龄生命表方法,设置不同强度(0,0.50,0.70 m W/cm2) UV-B连续多代处理麦长管蚜成虫,统计经紫外处理后的麦长管蚜第22代,第27代,第32代,第37代麦长管蚜生命表种群参数的变化并总结了1—37代麦长管蚜内禀增长率的变化规律。结果表明:(1)处理组供试麦长管蚜平均世代周期(T)呈先显著升高后下降的趋势。(2)低强度处理组内禀增长率(rm)、净增殖率(R0)、周限增长率(λ)均呈先升高后下降又升高的趋势,高强度处理组供试麦长管蚜内禀增长率(rm)、净增殖率(R0)、周限增长率(λ)呈先下降后显著升高的的趋势,且均在G37达到最大值。(3) 1—37代处理组麦长管蚜rm呈现先显著增高后下降又升高又下降又显著升高的变化规律,且均在G37达到最大值。由此可见:麦长管蚜经过多代的UV-B胁迫后,对其生命表参数的影响依然显著,在G37麦长管蚜对紫外的适应能力最强。本研究的创新点在于解析了第22代以后紫外胁迫对麦长管蚜种群动态的影响,从而为全面深入的阐述紫外胁迫对麦长管蚜生长繁殖的影响规律,掌握不同紫外胁迫下的剂量效应关系及麦长管蚜的适应性提供实验基础和理论依据。     

Alternaria alternata, a new pathotype pathogenic to aphids

A fungus, identified as Alternaria alternata, was isolated from dying or dead aphids and proved to be pathogenic. It was isolated from different parts of Greece from aphid specimens on cultivated plants, ornamentals and weeds. In the laboratory, disease development started with the germination of spores on the insect integument and the subsequent growth of mycelium. The fungus formed apical and intercalary, globose or lobate appressoria which were firmly attached onto the host exoskeleton and facilitated entrance of the mycelium into the insect body. Under favorable conditions of temperature (15–35 °C) and relative humidity (100%), infected aphids died in 2–4 days. A characteristic brown discoloration accompanied the death of the insects. Both mycelial growth and sporulation were profuse on dead specimens. The pathogen infected all 26 aphid species tested but was unable to infect other insects (Drosophila melanogaster and Ceratitis capitata) or aphid host plants. There were significant differences in mortality rate among aphid species only during the first two days after inoculation. It is suggested that A. alternata may be a good candidate to be exploited for the biological control of aphids.     

Aphelinus albipodus(Hymenoptera: Aphelinidae) andDiaeretiella rapae(Hymenoptera: Braconidae) Parasitism onDiuraphis noxia(Homoptera: Aphididae) Infesting Barley Plants Differing in Plant Resistance to Aphids

Russian wheat aphid,Diuraphis noxia(Mordvilko), as a pest of small grains, has prompted research into biological control and host plant resistance. In the presence of Russian wheat aphid, leaves of a susceptible barley (Morex) are curled and chlorotic and sustain large densities of this aphid, while leaves of a resistant barley (STARS-9301B) remain flat and green and sustain fewer aphids. Might parasitism of Russian wheat aphid byAphelinus albipodusHayat & Fatima andDiaeretiella rapaeMcIntosh be affected differently by these plant types? When presented the plants separately and based on parasitism rate relative to aphid density, the largerD. rapaewas more effective in parasitizing relatively high densities of aphids within curled leaves of Morex than relatively low densities of aphids on uncurled leaves of STARS-9301B. Parasitism byA. albipodusdid not significantly differ among the plants. When given a choice of plants, approximately equal rates of parasitism occurred on the two plant lines for both parasitoid species, and parasitism byD. rapaewas greater thanA. albipodus.These data indicate that using parasitoid size as an indicator of success in a physically restricted environment may be misleading, when considered in a plant environment responsive in several manners to aphids (chlorosis, curling, and ability to sustain Russian wheat aphid). We expect that use of resistant barley will result in decreased parasitoid abundance as aphid densities decrease. However, parasitism rates are expected to be approximately equal on resistant and susceptible barley. In this system, plant resistance and biocontrol are compatible management strategies.     

Effect of exposure to fluoride,nitrogen compounds and SO2 on the numbers of spruce shoot aphids on Norway spruce seedlings

Summary Development of spruce shoot aphid (Cinara pilicornis Hartig) populations was monitored in natural and artificial infestations of Norway spruce (Picea abies Karst.) seedlings, exposed to air pollutants in an experimental field. The pollutants, applied both singly and in mixtures, were gaseous sulphur dioxide, NaF (30 mg l^-1 F) and Ca(NO₃)₂ or (NH₄)₂SO₄ in aqueous solutions (200 mg l^-1 N). Aphid numbers on 10 seedlings in each treatment and two control plots were counted at 2-week intervals. At the beginning of the experiment aphid numbers did not differ between treatments. Aphid populations peaked in late June and early July. All the pollutants and their combinations significantly increased the numbers of aphids per seedling. Four apterous females were transferred to spruce seedlings which were growing in containers in the same plots. After 4–5 weeks aphid numbers were significantly higher in the fluoride treatment and in the combined treatment of fluoride, nitrogen and SO₂. The pollution treatments did not have a significant effect on shoot growth. Concentrations of F and S in needles were higher in treatments involving these pollutants. There were no significant differences in the concentrations of free amino acids in shoot stems between control and fluoride treatment. However, the relatively low concentration of arginine in the F treatment at the end of the growing season might indicate disturbances in the nitrogen metabolism of spruce seedlings.     

Control of whitefly, Trialeurodes vaporariorum and cotton aphid, Aphis gossypii in glasshouses by two isolates of the fungus, Verticillium lecanii

The abilities of two isoiates of the entomopathogenic fungus, Verticillium lecanii (one isolated from whitefly and one from aphids), to control both aphids and whitefly on glasshouse cucumbers was investigated. Control of homologous hosts was better than that of heterologous hosts. A single spray of a commercial substrate-containing formulation of the ‘whitefly’ isolate controlled established whitefly populations satisfactorily on sprayed foliage and also when the whitefly moved up to younger untreated foliage. In addition, because the substrate permitted growth and sporulation of the fungus on leaf surfaces, whitefly populations introduced after a V. lecanii application were also controlled. Control of whitefly by the ‘aphid’ isolate alone was unsatisfactory although control could be obtained in conjunction with the hymenopterous parasite Encarsia formosa. Control of Aphis gossypii by the ‘aphid’ isolate was obtained by spraying a commercial formulation containing a substrate but not by spraying pure spore suspensions. The ‘whitefly’ isolate did not control aphids satisfactorily. The difference between the two isolates in pathogenicity for aphids and whitefly was supported by laboratory infectivity experiments.     

Genetic variation in the effect of a facultative symbiont on host-plant use by pea aphids

Ecological specialisation on different host plants occurs frequently among phytophagous insects and is normally assumed to have a genetic basis. However, insects often carry microbial symbionts, which may play a role in the evolution of specialisation. The bacterium Regiella insecticola is a facultative symbiont of pea aphids (Acyrthosiphon pisum) where it is found most frequently in aphid clones feeding on Trifolium giving rise to the hypothesis that it may improve aphid performance on this plant. A study in which R. insecticola was eliminated from a single naturally infected aphid clone supported the hypothesis, but a second involving two aphid clones did not find the same effect. We created a series of new pea aphid–R. insecticola associations by injecting different strains of bacteria into five aphid clones uninfected by symbionts. For all aphid clones, the bacteria decreased the rate at which aphids accepted Vicia faba as a food plant and reduced performance on this plant. Their effect on aphids given Trifolium pratense was more complex: R. insecticola negatively affected acceptance by all aphid clones, had no effect on the performance of four aphid clones, but increased performance of a fifth, thus demonstrating genetic variation in the effect of R. insecticola on pea aphid host use. We discuss how these results may explain the distribution and frequency of this symbiont across different aphid populations. Julia Ferrari and Claire L. Scarborough contributed equally to the work.     

The impact of nutrition on spore yields for various fungal entomopathogens in liquid culture

Spore yields were measured for various fungal entomopathogens grown in six nutritionally different liquid media with low and high carbon concentrations (8 and 36 g l^–1, respectively) at carbon-to-nitrogen (C:N) ratios of 10:1, 30:1 and 50:1. Six fungi were tested: two Beauveria bassiana strains, three Paecilomyces fumosoroseus strains and one Metarhizium anisopliae strain. Spore yields were examined after 2, 4 or 7 days growth. In general, highest spore yields were obtained in media containing 36 g/l and a C:N ratio of 10:1. After 4 days growth, highest spore yields were measured in the three Paecilomyces isolates (6.9–9.7 × 10⁸ spores ml^–1). Spore production by the B. bassiana isolates was variable with one isolate producing high spore yields (12.2 × 10⁸ spores ml^–1) after 7 days growth. The M. anisopliae isolate produced low spore concentrations under all conditions tested. Using a commercial production protocol, a comparison of spore yields for the coffee berry borer P. fumosoroseus and a commercial B. bassiana isolate showed that highest spore concentrations (7.2 × 10⁸ spores ml^–1) were obtained with the P. fumosoroseus isolate 2-days post-inoculation. The ability of the P. fumosoroseus strain isolated from the coffee berry borer to rapidly produce high concentrations of spores prompted further testing to determine the desiccation tolerance of these spores. Desiccation studies showed that ca. 80% of the liquid culture produced P. fumosoroseus spores survived the air-drying process. The virulence of freshly produced, air-dried and freeze-dried coffee berry borer P. fumosoroseus blastospores preparations were tested against silverleaf whiteflies (Bemisia argentifolii). While all preparations infected and killed B. argentifolii, fresh and air-dried preparations were significantly more effective. These results suggest that screening potential fungal biopesticides for amenability to liquid culture spore production can aid in the identification of commercially viable isolates. In this study, P. fumosoroseus was shown to possess the production and stabilization attributes required for commercial development.     

FTIR spectroscopy as a potential tool to analyse structural modifications during morphogenesis of Candida albicans

Candida albicans is a polymorphic organism that grows under certain conditions as blastospores, hyphae or pseudohyphae. The potentials of FTIR spectroscopy for assessing structural differences in C. albicans blastospores and hyphae were investigated. The main observed differences were localised in the polysaccharide (950–1,185 cm⁻¹), protein (1,480–1,720 cm⁻¹), and the fatty acids (2,840–3,000 cm⁻¹) regions. Quantitative evaluation of differences between hyphae and blastospores by curve-fitting of these regions indicate that these modifications could be due to both changes in structure and content of components of the cell wall such as β-glucans, mannoproteins, and lipids. Furthermore, glycogen consumption could be involved during hyphae elongation. Thus, FTIR spectroscopy can be an interesting tool to investigate differences in structure and in content between blastospores and hyphae. We also demonstrate through this study that differentiation of C. albicans clinical strains using hyphae is feasible, as this has been previously shown with blastospores. This preliminary work on identification of C. albicans using hyphae is a prelude to a larger clinical study for early typing within 7 h from a pure culture.     

Cost-benefits of reduced aphicide usage on dwarf hops susceptible and partially resistant to damson-hop aphid

Soil‐applied imidacloprid at full (125 g a.i. ha^?1) and half approved doses gave levels of control of damson‐hop aphid, (Phorodon humuli), similar to that provided by foliar spray(s) of tebufenpyrad on the aphid‐susceptible dwarf hop cvs First Gold and Herald. On those cultivars, aphid control was unreliable on plots treated with quarter dose imidacloprid and was generally no better than on untreated plants. Aphids were virtually eliminated from the leaves by the end of July each year in all treatments consistent with the action of natural enemies. Aphid contamination of cones reflected the numbers on foliage at flowering time, but varied widely between years. Yields and percentage α‐acids content of dried hops were unaffected by the numbers of aphids on leaves early in the season and in cones at harvest, but aphid contamination reduced the economic values of crops by as much as 80%. Few P. humuli colonised the partially aphid‐resistant breeding line 23/90/08 before their numbers were regulated and consistent with natural enemy activity. Yields, percentage α‐acids content, and commercial value of harvested cones were similar in all treatments on 23/90/08 whether or not plants were treated with aphicides. The commercial risks posed by P. humuli preclude substantial reductions in aphicide usage on aphid‐susceptible dwarf hop cultivars, but future cultivars expressing a similar level of partial resistance to aphids as 23/90/08 should not need treatment with aphicides.     

Optimization of <Emphasis Type="Italic">Verticillium lecanii</Emphasis> spore production in solid-state fermentation on sugarcane bagasse

Verticillium lecanii is an entomopathogen with high potential in biological control of pests. We developed a solid-state fermentation with sugarcane bagasse as carrier absorbing liquid medium to propagate V. lecanii spores. Using statistical experimental design, we optimized the medium composition for spore production. We first used one-factor-at-a-time design to identify corn flour and yeast extract as the best carbon and nitrogen sources for the spore production of V. lecanii. Then, we used two-level fractional factorial design to confirm corn flour, yeast extract, and KH₂PO₄ as important factors significantly affecting V. lecanii spore production. Finally, we optimized these selected variables using a central composite design and response surface method. The optimal medium composition was (grams per liter): corn flour 35.79, yeast 8.69, KH₂PO₄ 1.63, K₂HPO₄ 0.325, and MgSO₄ 0.325. Under optimal conditions, spore production reached 1.1 × 10¹⁰ spores/g dried carrier, much higher than that on wheat bran (1.7 × 10⁹ spores/g initial dry matter).