Effects of clove oil,essential oil of Lippia alba and 2‐phe anaesthesia on juvenile meagre,Argyrosomus regius (Asso, 1801)

The objectives of this experiment were to (i) determine the efficacy of essential oils of clove (CO) and Lippia alba (EOLA) to induce deep anaesthesia in juvenile specimens (49.0 ± 6.2 g body mass, 16.6 ± 0.8 cm; n = 8 per treatment) of meagre (Argyrosomus regius); and (ii) study the feasibility of these substances, together with 2‐phenoxyethanol (2‐PHE), as potential sedatives [low concentration: (i) EOLA: 12 mg L^?1; (ii) CO: 1 mg L^?1; and (iii) 2‐PHE: 33 mg·L ^?1; n = 8 per treatment] for live fish transport of this species. All test were performed at a constant temperature (18°C). Thus, the main primary stress indicator (plasma cortisol) and secondary factors (plasma metabolites) were evaluated. In addition, growth hormone (GH) mRNA expression was also evaluated in the pituitary gland. The results indicated that EOLA is considered to be effective for deep anaesthesia when the concentration is close to 160 mg L^?1, while CO produces the same effect when lower concentrations are added (40–50 mg L^?1). Regarding sedative concentrations, a significant ~3‐fold increase in plasma cortisol levels was detected in the EOLA group when compared to control specimens. In addition, glucose levels were not reduced and significantly increased (~1.6‐fold) for 2‐PHE in relation to the control fish. None of the anaesthetics promoted a significant difference for GH expression with respect to the control group, but a significant ~2‐fold increase for 2‐PHE treatment with respect to the EOLA exposition was found in this gene expression. Results show that none of the anaesthetics analysed, at least in the ranges of concentrations used in this study (EOLA 12 mg L^?1, CO 1 mg L^?1, 2‐PHE 33 mg L^?1), are recommended for live fish transport, as shown by the absence of inhibition on the stress parameters assessed.     

Effects of different concentrations of 2‐phenoxyethanol on primary and secondary stress responses in Persian sturgeon,Acipenser persicus

The anaethetic effects of 2‐phenoxyethanol (2‐PE) on possible primary (cortisol level) and secondary (hematological indices and glucose level) stress responses were studied in Persian sturgeon (Acipenser persicus). Fish were first exposed to 0.1, 0.3, 0.5, 0.7, 0.9 and 1.1 ml L^?1 2‐PE, and the time to induction (deep anaethesia) and recovery were measured. At a concentration of 0.1 ml L^?1, 2‐PE failed to induce deep anaethesia in fish, whereas at concentrations of 0.7, 0.9 and 1.1 ml L^?1 all fish were anaethetized within 3 min of exposure. For assessing possible stress effects caused by effective concentrations of 2‐PE, the hematological indices, serum cortisol and glucose were determined in the deeply anaethetized fish as stress indicators. The 2‐PE exposure resulted in significant increases in red blood cell (RBC) values at 0.3 and 0.5 ml L^?1; parallel increases in hemoglobin values were also observed at these concentrations (P < 0.01). Moreover, a lower concentration of 2‐PE (0.3 ml L^?1) caused a significant increase in hematocrit values (P < 0.05). Among the hematological indices, mean corpuscular volume (MCV) values decreased at 0.5 ml L^?1 when compared with the control and other groups (P < 0.05). Serum cortisol level was elevated at 0.3, 0.5 and 0.7 concentrations of 2‐PE (P < 0.01). The glucose level followed a trend similar to that observed for cortisol. The outcome of these experiments shows that 2‐PE at a concentration of 0.9 ml L^?1 is a suitable anaesthetic for Persian sturgeon. This study demonstrates that rapid induction of deep anaethesia with a relatively high concentration of 2‐PE (0.9 and 1.1 ml L^?1) was associated with the lowest effects on signs of physiological stress in Persian sturgeon.     

Response of juvenile tench Tinca tinca (L.) to the anaesthetic 2-phenoxyethanol

The response of tench Tinca tinca aged 40–171 days post‐hatch (22–49 mm TL) to the anaesthetic 2‐phenoxyethanol was studied at 25°C. The lowest effective concentration of 2‐phenoxyethanol increased with age, while the highest safe concentration decreased. The fish aged 40 days post‐hatch required a significantly (P ≤ 0.05) shorter time to become anaesthetized than did older fish. The recovery time after 15 min of exposure to 2‐phenoxyethanol at 0.45 g dm^?3 was significantly shorter in the 40‐day‐old fish than in older fish. In juveniles of the same age, induction time or recovery time did not depend on their size or condition (Fulton's coefficient). At 25°C, 2‐phenoxyethanol at 0.5 g dm^?3 may be used to efficiently and safely anaesthetize T. tinca juveniles.     

Toxicity of ammonia and nitrite to yellow catfish (Pelteobagrus fulvidraco)

The 96‐h LC₅₀ (median lethal concentration, LC₅₀) tests were conducted using four different sizes of yellow catfish Pelteobagrus fulvidraco to provide primary information on the sensitivity of this species to elevated ammonia and/or nitrite, and to determine if the sensitivity is mediated by size under the same conditions. The results showed that 96‐h LC₅₀ of fish weighing 0.034 ± 0.002, 0.296 ± 0.049, 3.52 ± 0.95 and 32.96 ± 5.75 g to total ammonia nitrogen‐N was 24.96, 35.85, 47.44 and 68.79 mg L^?1, respectively; un‐ionized ammonia nitrogen‐N was 0.34, 0.49, 0.65 and 0.94 mg L^?1 in test conditions of pH 7.42 and 23°C; and that nitrite nitrogen‐N was 69.06, 97.23, 133.61 and 196.05 mg L^?1 in test conditions of pH 7.58 and 23°C, respectively. The NOEL (No Observable Effect Level) of fish (body weight from 0.03 to 30 g) to ammonia and nitrite was 2.25–6.22 mg L^?1 total ammonia nitrogen‐N, 0.03–0.10 mg L^?1 un‐ionized ammonia nitrogen‐N in test conditions of pH 7.42 and 23°C, and 6.27–17.68 mg L^?1 nitrite nitrogen‐N in test conditions of pH 7.58 and 23°C, respectively. These results indicate that the susceptibility of this fish to total ammonia or nitrite was reduced with increasing size, and that a dose‐dependent relationship might exist between them. The 96‐h LC₅₀ and NOEL of different sizes of fish to total ammonia, un‐ionized ammonia and nitrite would be important to know for water quality standards in yellow catfish aquaculture.     

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.     

Autogeny induced by a nonsteroidal ecdysone agonist tebufenozide in the mosquito Culex quinquefasciatus

The effects of tebufenozide, a nonsteroidal agonist of ecdysone, on egg development and reproduction in the anautogenic mosquito Culex quinquefasciatus Say (Culicidae, Diptera) are examined. The study population originates from Hyderabad, India. A dose‐dependent toxicity is observed when varying concentrations (10 µg L^?1 to 10 pg L^?1 ) of a flowable formulation of tebufenozide, known as Mimic 2F, are applied to first‐instar larvae in water. The median lethal dose (LC₅₀) against larvae is very low at 1.29 ng L^?1 H₂O. Doses below the LC₅₀ induce vitellogenesis in the females that subsequently emerge, and these females lay eggs autogenically (without blood feeding). Autogenous egg clutches are laid through three ovarian cycles. The number of eggs laid in each clutch is lower compared with an anautogenous clutch. An autogenic population has been maintained for over 15 generations after the primary induction, during which time the females have not been allowed to feed on blood. By comparison, doses higher than the LC₅₀ inhibit ovarian development. There is a gradual degeneration of the ovaries, and the females die approximately 20 days after imaginal ecdysis without commencing vitellogenesis. The results are discussed in relation to the endocrine and nutritional regulation of vitellogenesis in C. quinquefasciatus, and the possibility of using tebufenozide to regulate populations of some species of mosquito .     

Virulence of a South African isolate of the <Emphasis Type="Italic">Cryptophlebia leucotreta</Emphasis> granulovirus to <Emphasis Type="Italic">Thaumatotibia leucotreta</Emphasis> neonate larvae

Surface inoculation dose–response and time–response bioassays and detached fruit bioassays were conducted with a novel South African isolate of the Cryptophlebia leucotreta granulovirus (CrleGV-SA) against Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Noctuidae) neonate larvae. LC₅₀ and LC₉₀ values were estimated to be 4.095 × 10³ and 1.185 × 10⁵ OBs ml⁻¹, respectively. LT₅₀ and LT₉₀ values were estimated to be 4 days 22 h and 7 days 8 h, respectively, categorising the virus as a fast or type 2 granulovirus. There was a conspicuous difference in behaviour between larvae on inoculated diet and untreated diet, resulting in a significant reduction in penetration of diet. Bioassays on detached Navel oranges revealed LC₅₀ and LC₉₀ values of 9.310 × 10⁷ and 1.515 × 10⁹ OBs ml⁻¹, when using data on numbers of larvae per fruit rather than on numbers of infested fruit. Field trials will be conducted.     

Host plants influence susceptibility of whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) to the entomopathogenic fungus Isaria fumosorosea (Hypocreales: Cordycipitaceae)

We quantified the tritrophic effect of host plant on the susceptibility of the sweetpotato whitefly Bemisia tabaci (Genn.) to a fungal pathogen in the laboratory. Second-instar whiteflies reared on cucumber, eggplant, tomato and bean plants for six generations were exposed to conidial suspensions of Isaria fumosorosea isolate IF-1106. Our results did not detect differences in response (proportional survival or median lethal time, LT₅₀ days) among insect populations derived from different plants that were treated with 10⁷ conidia/ml. However, at concentrations ≤ 5×10⁶ conidia/ml, whiteflies reared on bean and tomato died significantly more quickly (i.e. LT₅₀ of 4–5 days) compared with cucumber and eggplant reared populations (5–7 days). Bean and tomato-reared populations were also more susceptible to mycosis (LC₅₀ ≈ 6 × 10⁵ conidia/ml) compared with those reared on cucumber (1.9 × 10⁶ conidia/ml) and eggplant (1.5 × 10⁶ conidia/ml). A separate study confirmed that this differential response of whitefly populations to I. fumosorosea was not explained by differences in deposition rate of conidia on leaf surfaces (i.e. a dosage effect). Our findings show that host plants affect the pathogenicity and virulence of a herbivore pathogen, but depend on the rate of exposure (inoculum) applied.     

Insecticidal Activity of the Leaf Essential Oil of Peperomia borbonensis Miq. (Piperaceae) and Its Major Components against the Melon Fly Bactrocera cucurbitae (Diptera: Tephritidae)

The essential oil from the leaves of Peperomia borbonensis from Réunion Island was obtained by hydrodistillation and characterized using GC‐FID, GC/MS and NMR. The main components were myristicin (39.5%) and elemicin (26.6%). The essential oil (EO) of Peperomia borbonensis and its major compounds (myristicin and elemicin), pure or in a mixture, were evaluated for their insecticidal activity against Bactrocera cucurbitae (Diptera: Tephritidae) using a filter paper impregnated bioassay. The concentrations necessary to kill 50% (LC₅₀) and 90% (LC₉₀) of the flies in three hours were determined. The LC₅₀ value was 0.23 ± 0.009 mg/cm² and the LC₉₀ value was 0.34 ± 0.015 mg/cm² for the EO. The median lethal time (LT₅₀) was determined to compare the toxicity of EO and the major constituents. The EO was the most potent insecticide (LT₅₀ = 98 ± 2 min), followed by the mixture of myristicin and elemicin (1.4:1) (LT₅₀ = 127 ± 2 min) indicating that the efficiency of the EO is potentiated by minor compounds and emphasizing one of the major assets of EOs against pure molecules.     

Various effects of ethanolic extract of Mentha pulegium on the two-spotted spider mite,Tetranychus urticae (Tetranychidae)

Ethanolic extract of Mentha pulegium was evaluated against the adults of important arthropod pest species, the two-spotted spider mite, Tetranychus urticae. Potential acaricidal impact of plant was determined by contact application. Phytotoxicity was recorded after 24 h. The value of LC₅₀ was 59,149 mg L^?1. Also, LT₅₀ values were 27.42, 25.56 and 19.79 h for 35,000, 50,000 and 100,000 mg L^?1, respectively. Also, results showed that this ethanolic extract had impact on repellency of T. urticae. All of the tested concentrations were similar in the repellency test. On the other hand, the used concentrations (1000, 4000, 6000 and 8000 mg L^?1) affected on the oviposition of mite females. These extract doses significantly decreased the egg laying on the treated surface. The current study indicated that this ethanolic extract can be used as a safe acaricide on T. urticae.     

Evaluation of the pathogenicity of Aschersonia aleyrodis on Bemisia tabaci in the laboratory and greenhouse

The entomopathogenic fungus Aschersonia aleyrodis (Webber) is a promising fungal species against whiteflies. In this work, the pathogenicity of A. aleyrodis isolate Aa005 against MEAM1 Bemisia tabaci (Gennadius) was evaluated under laboratory and greenhouse conditions. The bioassay results indicated that the percentage of larval mortalities was concentration and age dependent. A. aleyrodis showed high pathogenicity against second and third instars and pupae with LC₅₀ values of 7.93?×?10⁶, 1.08?×?10⁷, and 1.56?×?10^7?conidia?mL^?1, respectively. The median lethal time (LT₅₀) was lower (4.60 days) for second instars and was the highest (6.17 days) for pupae when inoculated with a concentration of 1?×?10^7?conidia?mL^?1. Weekly sampling of immatures showed that the per cent mortality caused by A. aleyrodis at a conidial concentration of 1?×?10^7?conidia?mL^?1 was 71.21% in small nymphs, 69.31% in large nymphs and 53.36% in pupae. The dispersion index (DI) and Lloyd’s Index of Patchiness (LIP) values indicated that the infected immatures had a tendency to aggregate. The study demonstrated that A. aleyrodis isolate A005 is an effective biocontrol agent for B. tabaci control under laboratory and greenhouse conditions.     

Toxicity assessment of insecticides commonly used in rice pest management to the fry of common carp, Cyprinus carpio, a food fish culturable in rice fields

Toxicity of four insecticides commonly used in rice pest management, chlorpyrifos, dimethoate, carbaryl and carbosulfan, to the fry of common carp was assessed through median lethal concentrations (LC₅₀) and in vivo inhibition of the brain acetylcholinesterase (AChE) enzyme at sublethal concentrations. The 96‐h LC₅₀ values for these four insecticides were determined to be 0.008, 26.11, 7.85 and 0.60 mg L^?1 respectively. Exposure of fish to a series of sublethal concentrations (0.5–5% LC₅₀) of each insecticide for 14 days resulted in concentration‐dependent inhibition in AChE activity in comparison with the controls. AChE activity was greatly inhibited in the fish exposed to sublethal concentrations of chlorpyrifos. Upon transfer to insecticide‐free water, AChE activities in fry exposed to 0.5 and 1% LC₅₀ concentrations of carbaryl and carbosulfan were restored to the control level within 7–21 days whereas the fish exposed to chlorpyrifos or dimethoate did not fully recover from the insecticide‐induced anticholinesterase action. Of the four insecticides tested, chlorpyrifos was the most toxic for the fry of common carp. Although dimethoate was least toxic for the fish under acute exposure, the restoration level of normal AChE activity was slower under chronic exposure in comparison with carbaryl and carbosulfan. Hence, the use of carbamates, especially carbaryl, to control insect pests of rice in rice‐cum‐carp culture systems is recommended when considering survival, restoration of the normal AChE activity and stamina of the cultured fish.     

Repellency and toxicity of a CO2-derived cedarwood oil on hard tick species (Ixodidae)

The repellency and toxicity of a CO₂-derived cedarwood oil (CWO) was evaluated against actively questing unfed nymphs of four species of hard ticks: Amblyomma americanum (L.), Dermacentor variabilis (Say), Ixodes scapularis Say, and Rhipicephalus sanguineus (Latreille). Using a vertical climb bioassay for repellency, nymphs of these species avoided a CWO-treated filter paper in proportional responses to treatment concentrations. At 60 min of exposure, I. scapularis nymphs were most sensitive with 50% repellency concentration (RC₅₀) of 19.8 µg cm^?2, compared with RC₅₀ of 30.8, 83.8 and 89.6 µg cm^?2 for R. sanguineus, D. variabilis and A. americanum, respectively. Bioassays determined the lethal concentration for 50% (LC₅₀) and 90% (LC₉₀) mortality of nymphs exposed to CWO in treated vials after 24- and 48-h exposure. After 24 h exposure, the LC₅₀ values were 1.25, 3.45 and 1.42 µg cm^?2 and LC₉₀ values were 2.39, 7.59 and 4.14 µg cm^?2 for D. variabilis, I. scapularis and R. sanguineus, respectively, but had minimal effect on A. americanum. After 48 h exposure, the LC₅₀ values were 4.14, 0.78, 0.79 and 0.52 µg cm^?2, and LC₉₀ values were 8.06, 1.48, 1.54 and 1.22 µg cm^?2 for A. americanum, D. variabilis, I. scapularis and R. sanguineus, respectively. The repellency of CWO on tick species decreased with time. The repellency and toxicity bioassays demonstrated concentration-dependent responses of tick nymphs to the oil, indicating the potential of the CO₂-derived cedarwood oil be developed as an eco-friendly repellent and/or acaricide.

     

Effects of Metarhizium anisopliae on searching,feeding and predation by Orius albidipennis (Hem., Anthocoridae) on Thrips tabaci (Thy., Thripidae) larvae

The generalist predator Orius albidipennis Reut. (Hem., Anthocoridae) and entomopathogenic fungus Metarhizium anisopliae (Metchnikoff) Sorokin (Ascomycota: Clavicipitaceae) are important biocontrol agents of Thrips tabaci Lindeman (Thys., Thripidae) in most greenhouses. In this study, we estimated searching time, feeding time and predation rate in O. albidipennis feeding on untreated and treated thrips larvae which had been inoculated with three concentrations of M. anisopliae V275 at four time intervals; 0, 24, 48 and 72 h after infestation. Applied concentrations were 1×10³, 2×10⁴ and 2×10⁵ conidia/mL which roughly correspond to the LC₂₅, LC₅₀ and LC₇₅ for second instar-larvae. O. albidipennis responded to the presence of the M. anisopliae on the treated hosts by increasing the searching time and decreasing feeding time and predation rate levels. It was also able to detect and avoid treated patches.     

Identification of a bacterium isolated from the diseased brown planthopper and determination of its insecticidal activity

The brown planthopper, Nilaparvata lugens, is one of the most harmful insect pests of rice crops in Asian countries. To find an effective biological control agent against this pest, we investigated the bacterial flora of field N. lugens collected from Jiangsu Province, China, in 2012 and tested its insecticidal activity. A novel bacterium strain, S-JS1, was isolated from N. lugens nymphs and adults and showed a high level of insecticidal activity. Based on its phenotypic, physiological and biochemical properties, and its 16S rRNA gene phylogeny, the isolate was assigned to Serratia marcescens; the name S. marcescens S-JS1 is proposed. The pathogenicity of S-JS1 against the third-instar nymphs, and the macropterous and the brachypterous adults of N. lugens were compared. The median lethal concentration (LC₅₀) values of S-JS1 against the brachypterous adult were the lowest (LC₅₀, 1.53?×?10⁸ colony forming units (cfu)/ml), followed against the macropterous adult (LC₅₀, 1.65?×?10⁹?cfu/ml) and third-instar nymphs (LC₅₀, 1.86?×?10⁹?cfu/ml) at 5 days post-infection. The median lethal time values of 8?×?10⁸?cfu/ml S. marcescens S-JS1 against the brachypterous adult, macropterous adult, and third-instar nymph were 4.5, 5.5, and 5.7 days, respectively. These results indicate that the S-JS1 isolate appears to be a promising S. marcescens strain with strong biocontrol potential against N. lugens.     

Comparative bioassay of different isolates of Bacillus thuringiensis subsp. kurstaki on the third larval instars of diamondback moth,Plutella xylostella (L.) (Lep.: Plutellidae)

The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae) is one of the most important pests of cruciferous plants throughout the world. In recent years, this insect has been a serious pest for cabbage fields in Tehran province. Resistance of P. xylostella to all main groups of insecticides has been recorded and it is ranked in the 20 most resistant pest species reported up to now. According to many researchers, to eliminate the problem of pest resistance to chemical pesticides, an integrated pest management programme should be used. In line with this, the uses of microbial control agents (MCAs) are discussed. The bacterium, Bacillus thuringiensis (Bt) is one of microbial control agents of pests. It is characterised by its ability to produce proteic crystalline inclusions during sporulation. Cry1 protein has insecticidal activity and is highly specific to certain insects and not toxic to unrelated insects, plants or vertebrates. In this work, the pathogenicity of some Bt isolates, including Dipel, 20, 29, 79 and 87, was tested against P. xylostella and the lethal concentrations (LC₅₀) of their crystal proteins to P. xylostella third larval instar was determined. The experiment was designed in factorial in randomised complete design with 5 treatments (different concentrations including 10⁴, 10⁵, 10⁶, 10⁷, 10⁸ CFU/ml and 5 replications and with 10 third larval instars. Spore–crystal complex was applied to the surface of natural diets (cabbage leaves) and the mortality of P. xylostella larvae was assessed 120?h after exposure of Bt toxin in each treatment. Results showed that percentage of survival was significantly higher for control treatment. Results also showed that after 5?days, LC₅₀ for isolates of Dipel, 20, 29, 79 and 87 were equal to 1?×?10⁶, 1?×?10⁵, 5?×?10⁵, 4?×?10⁵ and 1?×?10⁴ CFU/ml, respectively. LT₅₀ were equal to 93.71, 48.04, 71, 40.49 and 75.28?h. Of and most the percentage larval mortality relate to attendance 87 and also at least percentage mortality is related to the groom Dipel.     

Susceptibility of apple clearwing moth larvae,Synanthedon myopaeformis (Lepidoptera: Sesiidae) to Beauveria bassiana and Metarhizium brunneum

Apple clearwing moth larvae, Synanthedon myopaeformis (Lepidoptera: Sesiidae) were found to be susceptible to infection by two entomopathogenic fungi: an indigenous fungus isolated from S. myopaeformis cadavers and identified as Metarhizium brunneum (Petch); and Beauveria bassiana isolate GHA. In laboratory bioassays, larvae exhibited dose related mortality after exposure to both the M. brunneum and Beauveria bassiana with 7 day LC₅₀'s of 2.9×10⁵ and 3.4×10⁵ spores/mL, respectively. Larval mortalities caused by the two isolates at 1×10⁶ spores/mL were not significantly different and 73% of the M. brunneum-treated, and 76% of the B. bassiana-treated larvae were dead 7 days post treatment, with LT₅₀'s of 5.5 and 5.1 days, respectively.     

Biological activity of Hyposidra talaca nucleopolyhedrovirus against all instar stages of a destructive tea pest Hyposidra talaca (Lepidoptera: Geometridae) in India

Hyposidra talaca (Walker) (Lepidoptera: Geometridae) is the most harmful pest of northeastern tea hub of India that devastates the tea production by feasting on the tea leaves. Hyposidra talaca nucleopolyhedrovirus (HytaNPV) is a natural enemy of the aforesaid pest, as it poses great obstruction in the multiplication of the pest by causing significant larval mortality. The study was undertaken to screen the virus activity against first to fifth instar H. talaca larvae. Early instar stages are found more susceptible than the late stages as they tend to reflect highest LC₅₀ value for fifth instar as 4.3 × 10⁷ POB/ml and lowest LC₅₀ value for first instar as 7 × 10⁴ POB/ml within seven days of inoculation. LT₅₀ values vary between 2.47 and 8.45 days for neonates to fifth instar. The high record of virulence of HytaNPV indicates its bright prospect as a useful microbial biopesticide.     

Histopathology and bioassay of Plathypena scabra granulosis virus

A granulosis virus was found infecting Plathypena scabra larvae in Iowa. The capsules averaged 377 ± 25 × 222 ± 19 nm. On the basis of light microscopical observations, the virus appeared to infect the epidermis, fat body, and tracheal matrix cells. The LC₅₀ and LC₉₅ were 6.7 × 10⁷ and 1.5 × 10⁹ capsules/acre, respectively. The LT₅₀ values varied from 3 to 9 days for 1 × 10¹² and 1 × 10⁸ capsules/acre, respectively.     

Effect of repeated in vitro sub-culturing on the virulence of Metarhizium anisopliae against Helicoverpa armigera (Lepidoptera: Noctuidae)

The effect of repeated conidial sub-culturing of Metarhizium anisopliae on its virulence against Helicoverpa armigera (Hübner) was studied. The LT₅₀ observed against third instar larvae of H. armigera for the first sub-culture was 3.4 days; it increased to 4.5 and 5.6 days for the 20th and the 40th sub-cultures, respectively. The LT₅₀ values after passage of the 40th sub-culture on H. armigera decreased to 4.4 and 3.7 days for the 40th (first in vivo) and the 40th (fifth in vivo) passages, respectively. Similarly, the LC₅₀ of M. anisopliae towards third instar larvae of H. armigera increased from the first sub-culture (0.17×10⁴) to (3.0×10⁴) for the 40th conidial transfers on potato dextrose agar and again decreased to 0.74×10⁴ and 0.23×10⁴ in the 40th (first in vivo) and the 40th (fifth in vivo) passage, respectively. Similar trends for LC₅₀ and LT₅₀ values were seen when sugarcane woolly aphid, Ceratovacuna lanigera Zehntner was used as a host. Significant variation in appressorium formation and cuticle-degrading enzyme production such as chitinase, chitin deacetylase, chitosanase and protease during subsequent sub-culturing and passage through H. armigera was observed. Though there was no effect on internal transcribed spacer (ITS) sequence pattern, interestingly, in randomly amplified polymorphic DNA (RAPD), significant differences in the band intensities and in the banding pattern for different sub-cultures of M. anisopliae were observed. As stable virulence towards the insect pest is desirable for commercialisation of a mycoinsecticide, such changes in virulence due to repeated in vitro transfer need to be monitored and minimised.