Production of Culex pipiens (Dip.: Culicidae) adults infected by Strelkovimermis spiculatus (Nematoda: Mermithidae) in autodissemination control strategy

Biological Control of mosquito vectors with insect parasitic nematodes is of importance in Integrated Mosquito Management (IMM) due to its benign nature. The mosquito parasitic mermithid Strelkovimermis spiculatus normally parasitizes larval stages of Culex pipiens and rarely do adults of Culex get infected by this nematode in wild. This infrequent phenomenon is assumed as the way of nematode dispersal. We hypothized that infected mosquito adults can be obtained through laboratory manipulations. Parasite: host ratio and host stage were two main parameters to consider. To determine the optimal larval instar and parasite:host ratio, late third, early fourth, late fourth instar larvae and 5:1, 10:1, 20:1, 40:1 ratios were compared and the percentage of infected adult mosquitoes obtained recorded. Average nematode emergence time was measured to to estimate the proper release time of the mosquitoes in larval habitats. The sex ratio, number and length of postparasites emerged from adults were also calculated and compared in quality control process. Only late fourth instars infected adult host at 5:1 with a maximum proportion of infected adults of 17.39%. The ratio of 10:1 was chosen as standard infection ratio (P=0.87). The average duration between infection and nematode emergence was 7.37±0.51 (days). The proportion of females to total emerged nematodes from adults was 0.4:1 which is an acceptable ratio for nematodes’ colonization in water bodies. There was no statistical difference between the length of nematodes emerged from mosquito adults and larvae (P=0.14). Infecting late fourth instars individually at 10:1 infection ratio in an aliquot of nematode suspension and release of infected males seven days post-infection is a feasible strategy for application of this nematode in wild

Activation of Bacillus thuringiensis Cry1I to a 50 kDa stable core impairs its full toxicity to Ostrinia nubilalis

Bacillus thuringiensis Cry1I insecticidal proteins are structurally similar to other three-domain Cry proteins, although their size, activity spectrum, and expression at the stationary phase are unique among other members of the Cry1 family. The mode of action of Cry1 proteins is not completely understood but the existence of an activation step prior to specific binding is widely accepted. In this study, we attempted to characterize and determine the importance of the activation process in the mode of action of Cry1I, as Cry1Ia protoxin or its partially processed form showed significantly higher toxicity to Ostrinia nubilalis than the fully processed protein either activated with trypsin or with O. nubilalis midgut juice. Oligomerization studies showed that Cry1Ia protoxin, in solution, formed dimers spontaneously, and the incubation of Cry1Ia protoxin with O. nubilalis brush border membrane vesicles (BBMV) promoted the formation of dimers of the partially processed form. While no oligomerization of fully activated proteins after incubation with BBMV was detected. The results of the in vitro competition assays showed that both the Cry1Ia protoxin and the approx. 50 kDa activated proteins bind specifically to the O. nubilalis BBMV and compete for the same binding sites. Accordingly, the in vivo binding competition assays show a decrease in toxicity following the addition of an excess of 50 kDa activated protein. Consequently, as full activation of Cry1I protein diminishes its toxicity against lepidopterans, preventing or decelerating proteolysis might increase the efficacy of this protein in Bt-based products

Report of Eristalis similis (Diptera: Syrphidae) from Iran

During a survey conducted on Syrphidae fauna in Guilan province (Masuleh & Lakan) in August 2006, some species of the genus Eristalis Latreille were collected and identified, of which E. similis (Fallen) is newly reported from Iran. The identification was confirmed by Heikki Hippa, Swedish Musem of Natural History

Olfactory response of the predatory bug, Orius niger (Hem.: Anthocoridae) to Tetranychus urticae (Acari: Tetranychidae) on cucumber leaves treated or untreated by Beauveria bassiana

Olfactory experiments were performed to study the predation behavior of Orius niger Wolff (Hemiptera: Anthocoridae) on the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) in presence or absence of Beauveria bassiana (Bals.). The experiments were carried out with six day old female bugs by recording the predator direction towards each of the Y-tube olfactometer arms and through three dependent replicates consisted of 15 replicates each. The predatory bug showed a significant preference towards the odors related to infested cucumber leaves by T. urticae in the absence of fungus and when the predator received odors related to T. urticae infested leaves v.s. B.bassiana fungus treated, spider mite infested leaves (72 hours). There was no significant difference in the predator olfactory experiment when the alternative arms consisted of treated v.s. untreated spider mite infested cucumber leaves (0, 24 and 48 hours after treatment). The results showed the capacity of the predatory bug to recognize the patches infected by B.bassiana fungus and successfully avoiding it

Transmission possibility of the fungus Beauveria bassiana KCF102 by mating behavior between Sunn pest, Eurygaster integriceps (Hem.: Scutelleridae) adults

Horizontal transmission of an isolate of the etomopathogenic fungus, Beauveria bassiana KCF102, was examined by allowing inoculated Eurygaster integriceps Put. adults to mate with non-inoculated ones. In case of susceptibility to B. bassiana, there was no significant difference between the males and females. However, there was significant difference among treatments for mortality of non-inoculated adults. It meant horizontal transmission could be happened between the inoculated and non-inoculated adults. Recording no significant difference among the treatments of the inoculated males + non-inoculated males and treatment with inoculated females + non-inoculated males revealed that this kind of horizontal transmission was not merely due to the mating behavior, given that the same transmission could be existed between inoculated and non-inoculated males or between those of female adults. There was significant difference for mortality percentage of adults among the five body-part treatments, ranging from 16.6 to 48.9, with the highest mortality for total body treatment and the lowest one for the pronotum

A laboratory investigation on virulence of Metarhizium anisopliae on Thrips tabaci (Thys.: Thripidae) and its predator, Orius albidipennis (Hem.: Anthocoridae)

In the present study, virulence of three isolates of Metarhizium anisopliae (Ascomycota, Clavicipitaceae) were evaluated on the second instar larvae of the onion thrips, Thrips tabaci Lindman by using spray potter tower at six conidial concentrations of isolates (103-108 conidia/ml) with Thrips Entomopathogenic Bioassay System (TEBS) method. Causing the highest total mortality rate on thrips larvae and having the lowest LC50 value (2.3 Ã 104 conidia/ml), M. anisopliae EUT118 was selected as the highest virulent isolate. Afterwards, the susceptibility of female adults and 5th nymphs of Orius albidipennis (Reuter) was tested against this isolate of M. anisopliae without attendance of host. Results indicated that two stages of predator; female adults and 5th instar nymphs had similarly low susceptibilities to fungal infection. In general, our results revealed that the anthocorid predator, O. albidipennis was less affected by this isolate of fungus. As a result, these two biocontrol agents could be used both together in control programs of T. tabaci in greenhouses

Study on potential of some solid natural substances in production of Beauveria bassiana (Ascomycota, Cordycipitaceae) conidia

In this study, two fungus isolates, Beauveria bassiana EUT105 and B. bassiana EUT116, were evaluated for production of aerial conidia on wheat, wheat flour, wheat bran, rice flour, rice bran, rice paddy, millet and corn flour using two phasic liquid-solid system. Data analysis showed that there are significant differences among treatments (simple media) in both isolates. In B. bassiana EUT105, the maximum and minimum productions were achieved on wheat bran, 2.3 Ã 1010 conidia/g and on rice paddy, 1.5 Ã 109 conidia/g of medium, respectively. In B. bassiana EUT116, wheat bran with 6.1 Ã 109 conidia/g and millet with 8 Ã 108 conidia/g had the maximum and minimum productions, respectively. Effect of adding nutritional complementary compounds to the growth media was significant in increasing of conidial yield. Related results showed that adding permeate increased the production but molasses did not it in comparison with control in both isolates. Wheat bran plus permeate had the maximum production, 5 Ã 1010 and 4.6 Ã 1010 conidia/g in B. bassiana EUT105 and EUT116, respectively and minimum production was obtained with rice flour plus molasses, 1.5 Ã 108 and 6 Ã 108 conidia/g in B. bassiana EUT105 and EUT116, respectively

Evaluation of the effect of MbNPV on cabbage moth, Plutella xylostella (Lep.: Plutellidae), in laboratory conditions

Cabbage moth, Plutella xylostella L., is the most important pest in cabbage and canola cultures in Iran. Nuclear polyhedrosis viruses are known as important natural enemies of this pest. Because of economic importance of cabbage moth and the necessity of its control, MbNPV (Baculoviridae) was chosen to evaluate its effect on cabbage moth. Experimental data showed that the virus had high virulence and could be considered as the important agent for the control of this insect. In infestation of egg surfaces with 1 Ã 105 PIB/ml of MbNPV, all of larvae died three days after hatching. The LC50 value for the second instar larvae of cabbage moth was calculated 11.99 PIB/mm2. The LT50 values for the same larvae with 19.5 and 47.86 PIB/mm2 doses of MbNPV were 7.16 and 6.11 days, respectively. Mean percentages of mortality with 47.86 PIB/mm2 for 2nd, 3rd and 4th instar larvae were 74.44, 42.78 and 11.11, respectively

Effect of midgut proteolytic activity on susceptibility of lepidopteran larvae to Bacillus thuringiensis subsp. Kurstaki

Bacillus thuringiensis (Bt) is the most effective microbial control agent for controlling numerous species from different insect orders. All subspecies and strains of B. thuringiensis can produce a spore and a crystalline parasporal body. This crystal which contains proteinaceous protoxins is dissolved in the alkaline midgut, the resulting molecule is then cleaved and activated by proteolytic enzymes and acts as a toxin. An interesting aspect of this activation process is that variations in midgut pH and protease activity have been shown to account for the spectrum of some Bt proteins activity. Thus, an important factor that could be a determinant of toxin activity is the presence of proteases in the midgut microenvironment of susceptible insects. Reciprocally, any alteration in the midgut protease composition of the host can result in resistance to Bt. Here in this paper, we reviewed this processes in general and presented our assays to reveal whether resistance mechanism to Bt in Diamondback Moth larvae could be due to the function of the midgut proteases? We estimated LC50 for both probable susceptible and resistant populations in laboratory and greenhouse tests. Then, the midgut protease activities of the B. thuringiensis in