Please use this identifier to cite or link to this item: http://prr.hec.gov.pk/jspui/handle/123456789/15778
Title: Host specific variations in citrus leafminer, Phyllocnistis citrella Stainton herbivory, damage and effects on net photosynthetic rates of different citrus cultivars
Authors: Arshad, Muhammad
Keywords: Agriculture and Veterinary Sciences
Entomology
Issue Date: 2019
Publisher: University of Sargodha, Sargodha.
Abstract: Citrus leafminer (CLM), Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae) is a major insect pest of citrus and cause extensive damage in both nurseries and orchards in Pakistan. Feeding by CLM larva exposes leaf cuticle to the causal pathogens of the citrus canker disease as well as effect indirectly on photosynthetic activity that can cause greater losses than the direct removal of leaf area. The seasonal incidence of CLM in Citrus reticulata Blanco orchards was determined in the three most growing citrus tehsils (Kotmomin, Bhalwal and Sargodha) of Pakistan, during 2014-15. The significantly higher population of CLM was observed in May and September during both study years. While in January-March the CLM populations were observed minimum during both study years. The abiotic factors such as temperature showed significantly (P<0.05) positive correlation with CLM infestation, however, humidity did not show any significant (P>0.05) effect on CLM infestation during both years. The feeding preference of CLM was evaluated on ten citrus cultivars and also the relation of leaf morphological characters and trace elements of different citrus cultivars with CLM intensity was determined. The results showed that percent infestation of CLM was 99.3%, 92.6%, 92.0% and 91.3% on Grapefruit, Fairchild, Kinnow and Succari cultivars respectively at the last day of observation during summer of 2015 and proved as most susceptible cultivars for CLM. During Fall 2015, the percent CLM infestation was more than 80% on all citrus cultivars except Salustiana, seedless Lemon and Musambi. Similar results were observed during Summer-2016 for percent CLM infestation. However, the least affected cultivars from CLM infestation were Musambi and seedless Lemon during all three seasons. The CLM larval intensity was also higher on Fairchild, seedless Kinnow, Kinnow and Grapefruit and the least activity of CLM larvae was found on seedless Lemon and Musambi during all three seasons. No significant relation of leaf morphological characters and trace elements were observed with CLM larval intensity at P>0.05. The leaf area damage of different citrus cultivars due to mining activity of CLM was quantified. The total leaf area and mine area per leaf was calculated by image analysis method using Sigmascan Pro 5.0 software. The results of our study showed that CLM generated larger mines (1.64cm2 , 1.44 cm2 , 1.40 cm2 ) on Grapefruit, Kinnow and Succari respectively, compared to other cultivars. The percent leaf damage due to CLM larvae x feeding was also observed higher (44.2%, 36.5%, 36.3% and 35.8%) on Citrus tangerines (Fairchild) and Citrus mandarins (seedless Kinnow, Feutrell‘s early and Kinnow) respectively, which showed susceptibility to this insect pest. Smallest mines generated by CLM were found on China Lemon and Succari and the percent leaf damage was also found minimum on these two cultivars. Effect of CLM feeding damage on the photosynthetic rate (Pn), CO2 exchange rate, (Ci), H2O exchange rate (Wi), stomatal conductance (C) and transpiration rate (E) of various cultivars was tested. However, Fairchild, Kinnow and seedless Kinnow cultivars showed maximum reduction (97.3%, 94.2% and 86.3% respectively) in Pn. The Grapefruit cultivar initially showed a decreasing trend in Pn and then increased at the end. Furthermore, the correlation analysis was verified that C, E, Ci and Wi were significantly and positively correlated with Pn except in case of Grapefruit in which Ci and Wi was not significant (P>0.05). For eco-friendly management of CLM, first, the effectiveness of some synthetic insecticides and essential oils was assessed against CLM larvae in laboratory. Two laboratory bioassays, leaf dip bioassay (LDB) and topical bioassay (TB) were developed to check the efficacy in laboratory. As seen from results, abamectin showed significant mortality (63.5%) of CLM larvae when topical bioassay was performed. Similarly, the percent mortality of CLM larvae was 53.8% after application of abamectin, when leaf dip bioassay technique was used. However, among tested botanicals, Azadirachta indica A. Juss (Family: Meliaceae) oil showed better results with percent CLM mortality of 35.6%, through topical bioassay and 31.8% through leaf dip bioassay. In the case of A. indica, the LC50 value was also observed lower (1.88±0.373, 1.73±0.289) in LDB and TB respectively, as compared to other botanicals. Secondly, the aqueous and alcoholic extracts of some selected plant species were also tested against CLM larvae by two different bioassays. Highest CLM mortality was observed in the aqueous (61.17%) and alcoholic (58.3%) extracts of A. indica compared to rest of the plant extracts after 24 hours of exposure. Among two treatment application methods, higher CLM mortality was obtained in the topical application of A. indica extract than leaf dip application. Furthermore, the LC50 value of A. indica aqueous extracts was 6.8% in leaf dip bioassay as well as 4.55% in topical application which was lower compared to all other extracts. Musa acuminate and Citurs limon extracts (both aqueous and alcoholic) were xi found least effective against CLM larvae. When combined efficacy of plant extracts with abamectin was evaluated, the aqueous and alcoholic extract of A. indica combination treatments provided highest mortality (62.25% and 66.25% respectively) than the rest of the treatments. Third, the extracts of A. indica at 5% and 7% and its oil at 1% and 1.5% concentration were studied in comparison to synthetic insecticide abamectin 1.8% EC against CLM at nursery plantations. Two foliar application of each treatment during September-2015 and one during April-2016 were executed and the data of live larvae were recorded at 3rd and 7 th days after each application. The results showed that the control rate of all larval instars was higher with the application of abamectin and A. indica oil at 1.5% concentration during both seasons and there was no significant difference in their abilities to suppress the CLM larval population. In comparison to oil of A. indica, its extract was not well enough to suppress the CLM larval population. Likewise abamectin, the A. indica oil also gave better control of CLM larvae in nursery plantations and should be a part of the integrated management program. Furthermore, the natural mortality factors of CLM were assessed in Citrus valencia and Grapefruit orchards at Fort Pierce, Florida, USA. Results from both orchards clearly showed that predation of CLM was about 40-59% during June and August, however the parasitism rate was higher in the month of July which was about 50-55%. Ageniaspis citricola Logvinoskaya (Hymenoptera: Encyrtidae) population contribute in CLM parasitism comparatively high than Eulophid spp. The parasitism sign on CLM as well as the empty mines were observed on 20-25% leaves per shoot in both citrus hosts. Similarly, about 50- 88% mortality of CLM was found due to predation in unprotected (control) branches compared to cage barrier treatment in which no empty mine was observed, while the parasitism contributed the least (9-14%) to CLM mortality.
Gov't Doc #: 20926
URI: http://prr.hec.gov.pk/jspui/handle/123456789/15778
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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