No abstract

Background Insecticidal crystal proteins (encoded by cry genes) produced by Bacillus thuringiensis (Bt) are fatal for insects of different orders such as Lepidoptera. The genes that encoded these crystal proteins can be detected on plasmids and chromosomal DNA and show different types in various strains. Therefore, the objective of this study was to determine molecular characteristics of Iranian Bt strains as well as their toxicity against Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae). Results The collection sites included fields, gardens, and desert and semi-desert areas in 8 provinces of Iran. For crystal formation, each isolate was cultured in T3 medium. The results showed that the Bt isolates produced different types of crystals including spherical (73.33%), bipyramidal (53.33%), irregular (40%), cubical (33.33%), and elliptical (13.33%). Plasmid DNA extraction was performed and showed that most of the strains exhibited similar pattern in the number and the size of the plasmid bands to those of Bt kurstaki (Btk). Some specific primers were used for PCR amplification to distinguish different crystal genes including cry1 (A, C, and D) and cry2A (a and b). The primers related to cry1D and cry2Aa1 genes produced no amplicons. The results revealed that the most abundant gene was cry1-type. All strains analyzed for the cry2Ab2 gene presented unexpected bands. Electrophoretic profile of the protein crystals showed bands with different diversity in number, and size ranged from about 16 to 140 KDa. The bioassay result of some more toxic strains exhibited that the pathogenicity of 1019 was higher than the rest, even the reference strain, Btk. However, the toxicity of other strains was the same as Btk. According to the phylogenetic tree, 1019 was located in the same group with Bt subspecies coreanensis, Bt subspecies indiana and Bt subspecies tolworthi. Conclusions The investigated Iranian strains had the lepidopteran-active cry genes. The strains with the same toxicity to E. kuehniella had various cry genes, plasmid, and crystal protein profiles and vice versa. Therefore, characterization of cry genes of native strains could lead to access potent isolates as biocontrol agents against native insect pests.

Some demographic parameters of the indigenous parasitoid, Aphidius matricariae Haliday (Hymenoptera: Braconidae) parasitizing the greenbug, Schizaphis graminum (Rondani) (Hemiptera: Aphididae), were estimated at 3 different temperatures (20, 25, and 30 ± 1 °C; 70 ± 5% RH; 16 L:8D). According to age-specific theory, the demographic parameters of the parasitoid were computed by related formulas. The results showed that duration of mummy’s formation to adult emergence and oviposition to adult emergence were significantly prolonged at 30 °C. The high temperature (30 °C) markedly shortened the longevity and lifespan of the wasp. The lowest value of fecundity (6.35 ± 0.85) significantly occurred when the female wasps were exposed to 30 °C. The estimated values of rm were remarkably high when the female wasps were exposed to 20 (0.320 ± 0.011) and 25 °C (0.310 ± 0.009). The lowest and highest values of the R0 significantly occurred at 30 (6.167 ± 0.754) and 20 °C (55.306 ± 6.316). The λ, T, DT, and rw values were noticeably decreased at high temperature, and there was non-significant difference between the two other temperatures. High temperature decreased the number of females produced per female per day (mx) and survival rate (lx) of the parasitoid wasp. The highest mx and lx happened at 20 and 25 °C, respectively. Therefore, the results showed that the parasitoid wasp was sensitive to the high temperature, as its low reproduction, survival, and short adult longevity were recorded. Considering the characteristics, the wasp appeared to be well-adapt with the temperatures below 30 °C. Understanding the optimal temperatures for the life history traits of A. matricariae could promote the performance of the parasitoid wasp in different climatic regions, and this might advance the mass production of the parasitoid applied in IPM program for successful biological control of S. graminum.

Aphids can have devastating effects on agriculture and horticulture, and biological control agents form an important means of controlling them.Aphidius matricariaeHaliday is an important endoparasitoid for the suppression of aphid pest population outbreaks. In this research, the influence of three different temperatures, 20, 25 and 30°C, on some life cycle charactersitic ofA. matricariaewas studied under laboratory conditions when present on its host,Aphis fabaeScopoli. At 30°C, the intrinsic rate of increase, net reproductive rate, finite rate of increase, mean generation time and increase rate in one week were all significantly lower compared to the lower temperatures. The results showed that temperature had a significant effect on the duration of parasitoid development from oviposition to adult emergence. Moreover, the value of doubling time was higher at 30°C than at 20 and 25°C. The parasitoid had the shortest longevity, life span and lowest fecundity at 30°C. This investigation of temperature-dependent development and reproduction can help in the management of biological control programs. The results of this study demonstrate thatA. matricariaeis able to perform, and be mass produced, as a favorable and proper natural enemy for the biocontrol ofA. fabaeat a temperature range of 20-25°C.

No abstract