PLANT PEST RESEARCH
Year:2020 | Volume:10 | Issue:2|Papers Count:7

Wheat, Triticum aestivum L. is of one the most important cultivated crop plants that are grown extensively for food in the world. The green wheat aphid, Schizaphis graminum (Rondani) (Hem.: Aphididae) is an important pest of wheat in Iran causes severe damage to the crop. In this research, thermal requirements of parasitoid wasp, Diaretiella rapae (M'Intosh) (Hym.: Braconidae) on the green wheat aphid, Schizaphis graminum (Rondani) (Hem.: Aphididae) were assessed at five constant temperatures (10, 15, 20, 25 and 27. 5º C), 60± 5% RH and a photoperiod of 16L: 8D hours. The results showed that temperature had significant effect on developmental time. The mean of longest and shortest preimaginal period were observed at 10º C (25. 49± 0. 09 day) and 25º C (9. 24± 0. 05 day), respectively. Effect of temperature on developmental time of D. rapae was fitted using linear and non-linear models. The lower temperature threshold and thermal constant of D. rapae were 3. 21º C and 229. 36 DD, respectively using linear regression model. The non-linear model Berier 1 had relative high goodness-of-fit. T0, Topt and Tmax were fitted well using this model. Therefore, Berier 1 model was determined for the description of temperature-dependent development of D. rapae on S. graminum. In this research, the linear and most common nonlinear thermal models and the criteria for selecting appropriate models are evaluated.

Plant essential oils are secoundary metabolites that protect the plants against wide range of arthropods and plant pathogens. Encapsulation of essential oils can improve their stability and efficacy for pest control. In this study, the essential oil of Thymus daenensis Celak. (Lamiales: Lamiaceae) was extracted using hydro-distillation, and urea-formaldehyde nanocapsule of the essential oil was then prepared using in situ polymerization technique. In addition, the effects of sublethal concentrations (LC25) of pure and nanocapsulated formulations of T. daenensis essential oil on the life-table parameters of Brevicoryne brassicae L. (Hem.: Aphididae) were examined using leaf-dipping method under laboratory conditions. According to the obtained results, the intrinsic rate of increase (r) was 0. 16, 0. 21, 0. 29 and 0. 29 day-1 for nanocapsulated formulation, pure formulation, 1st control (distilled water + Tween 80 (0. 5%)) and 2nd control (distilled water), respectively. The finite rate of increase (λ ) was also significantly lower for aphids treated by nanocapsulated formulation (1. 17 day-1) than aphids in pure formulation treatment (1. 24 day-1), and 1st (1. 34 day-1) and 2nd (1. 33 day-1) control groups. Furthermore, the net reproductive rate (R0) was 5. 24 and 9. 84 nymphs for nanocapsulated and pure formulations, respectively, which were significantly lower than that for controls. The greatest and lowest mean generation time (T) were observed for the 2nd control (11. 25 days) and nanocapsulated formulation (10. 32 days), respectively. According to findings of this study, the nanocapsulated formulation of T. daenensis essential oil is recommended for use in the integrated pest management of B. brassicae.

In this study, the efficiency of colored traps (sticky colored and colored water traps) in thrips attraction in the legumes of Ilam province was investigated. The experiment was conducted in a completely randomized block design with four treatments (yellow, blue, white and green colors) and twelve replicates during two years. On average, the highest number of thrips in chickpea and lentil fields in the year 2019 were 12. 03± 0. 17 and 15. 79± 0. 14 and also in the year 2018 were 9. 88± 0. 15 and 13. 45± 0. 21 for blue sticky traps, respectively. Also the results of colored water traps showed that in both years, the highest average number of thrips for chickpea and lentil fields was related to blue water trap; so that the highest average number of thrips in chickpea and lentil fields in the year 2019 were 5. 29± 0. 13 and 7. 07± 0. 19 and in the year 2018 was 5. 22± 0. 13 and 5. 97± 0. 17, respectively. Also, according to the data, the highest rate of thrips attraction to colored sticky traps and colored water traps in chickpea and lentil fields was duting the flowering stage of host plants. Overall, the results showed that the efficiency of colored sticky traps was higher than colored water traps. Also, the use of blue and yellow colored traps is appropriate in the management control of thrips.

Tomato leaf miner, Tuta absoluta Meyrick (Lep.: Gelechiidae) is a invasive pest for country since 2010 and spread rapidly in different regions including Jiroft. Regarding the increased area of tomato cultivation under greenhouses conditions in this region, the unknown status of pest and its high potential for damage, the study of population fluctuation and determining the best area of the plant for sampling of pre-adult stages is very important to make reliable management decisions. In this study in a tomato cultivated greenhouse, leaves were weekly sampled to check various stages of insect growth including eggs, larvae, and leaf mines. The results showed that the insect activity observed from the middle of growing season and population density gradually increased to its peak in April and May. During this period of time, it reproduces 4-5 generations. The highest number of insect eggs was found on the upper half of the plants and mainly in the lower surface of the leaves. In addition, it was revealed that the sampling of leaf mines was more accurate than counting different developmental stages in estimating the population density of this pest. Based on Correlation test, it was found that there is a positive correlation between the changes in the number of leaf mines and density of larval population in the upper half of the plant. Accordingly, the population density of larvae can be estimated only by sampling the leaves in this section and counting the number of leaf mines.

The activity of Oryctes Hellwig (Coleoptera: Scarabaeidae) causes severe damage to date palm. In order to study spatial distribution, 23 date palm plantations as sampling areas were selected. Geostatistical methods were used to simulate spatial distribution models. Correlation and overlap indices of ecological niches were calculated. To investigate the temporal distribution, a plantation was randomly selected in Abadan, Shadegan and Behbahan areas and sampling was performed biweekly intervals. Time series models were used to study seasonal population fluctuations. The results showed that spatial distribution of the rhinoceros beetles, O. elegans and O. agamemnon were compatible with spherical and linear models, respectively. The effect of the fragment was approximately the same, at about 9. 7-9. 9 and variograms ranged from 3. 8 to 3. 2. According to the results, the relative probability (Oij) of O. elegans in 87. 5% of sampling points was higher than O. agamemnon. The overlap of ecological niches of the two species (D) ranged from 0. 94 to 1. Populations of the two species started their activity from late February to early March. Population growth for both species continued in spring and early summer. Population growth rate for O. elegans was more than O. agamemnon. The maximum population densities of O. elegans and O. agamemnon were calculated in June and July with a time difference of about one month in the two regions of Abadan and Shadegan, respectively. In Behbehan area, the peak population density for O. elegans and O. agamemnon was almost identical, in the second week of June. The results of this study could be used for control monitoring, designing an integrated management program and assessment on the risk of rhinoceros beetles.

Type and biochemical properties of the digestive proteases were determined using specific substrates and inhibitors in the larvae and the adults of Cryptolaemus montrouzieri and their activity changes were evaluated when fed on the different preys. Rearing of beetles was done in laboratory conditions and they were fed on citrus mealybug. Dissection was done in NaCl medium and the obtained midgut was homogenized and centrifuged. Then, the activity of digestive proteases determined by using the specific substrates and inhibitors by feeding on three hosts. The results showed that just cysteine proteases and exopeptidases were active in the midgut of adults while both serine and cysteine proteases were engaged in the digestion by the larvae. The highest activity of the serine proteases; trypsin, chymotrypsin and elastase, were found in the pH sets of 8, 8-9 and 9, respectively. The optimal pH of cathepsins B and L were determined in 6 and 5 pH values of the larvae and the adults of C. montrouzieri, respectively. The highest activities of digestive larval amino-and carboxypeptidases were measured at pH 7 while these two enzymes showed the highest activity at pH sets of 7 and 6 in the adults, respectively. The specific inhibitors including cystatin, E-64, TLCK, SBTI, TPCK and AEBSF. HCL significantly decreased the activities of specific proteases in the larvae and the adults of C. montrouzieri. No significant differences were observed in the activities of serine proteases, exopeptidases and cathepsin L in the larvae fed on Planococcus citri, Pseudococcus viburni and Toxoptera aurantii but cysteine proteases and aminopeptidases in the adults fed on tea aphid showed the least activity. The difference in proteolytic profile of the larvae and the adults of C. montrouzieri concur the physiological differences in these two developmental stages with the emphasize on serine proteases in the preservation and control of developmental status of digestive tract. In addition, the higher activity of cysteine proteases in the adults may be related to the nature of utilized prey and presence of different proteinaceous components or even glycoperoteins in the preys.

The hemolymph circulatory system and hemocytes play a direct role in insect’ s cellular defense. Changes in the shape, number and type of hemocytes are important indicators of an organism's reaction to infection or stress. In this study, larval hemocytes of Grapholita funebrana Treitsch were examined using light microscopy at 40 magnifications. Hemocytes were identified by Giemsa staining. Five types of hemocytes were identified in larvae of these insects as follows: granulocytes (GRs), plasmatocytes (PLs), oenocytoids (OEs), prohemocytes (PRs) and spherulocytes (SPs). Examination of the percentage of hemocytes in different larval instars of G. funebrana showed that granulocytes and plasmotocytes are the most abundant homocytes in fourth-and fifth-stage larvae. The differential number of hemocytes gradually increased as the larvae developed. Also, hemogram components including larval hemolymph volume and total number of hemocytes were determined. This study showed that volume of hemolymph and similarly the total number of hemocytes have a direct relation with the larval growth and body size. Grapholita funebrana is one of the most serious pests of plum orchards in Iran and immunological studies on this pest are rare. Thus, in the current study, types and number of cellular elements have been taken into consideration.