Azhar Abbas Khan

Use of Recombinant Tobacco Mosaic Virus To Achieve RNA Interference in Plants against the Citrus Mealybug, Planococcus citri (Hemiptera: Pseudococcidae)

The citrus mealybug, Planococcus citri, is an important plant pest with a very broad plant host range. P. citri is a phloem feeder and loss of plant vigor and stunting are characteristic symptoms induced on a range of host plants, but P. citri also reduces fruit quality and causes fruit drop leading to significant yield reductions. Better strategies for managing this pest are greatly needed. RNA interference (RNAi) is an emerging tool for functional genomics studies and is being investigated as a practical tool for highly targeted insect control. Here we investigated whether RNAi effects can be induced in P. citri and whether candidate mRNAs could be identified as possible targets for RNAi-based P. citri control. RNAi effects were induced in P. citri, as demonstrated by specific target reductions of P. citri actin, chitin synthase 1 and V-ATPase mRNAs after injection of the corresponding specific double-stranded RNA inducers. We also used recombinant Tobacco mosaic virus (TMV) to express these RNAi effectors in Nicotiana benthamiana plants. We found that P. citri showed lower fecundity and pronounced death of crawlers after feeding on recombinant TMV-infected plants. Taken together, our data show that actin, chitin synthase 1 and V-ATPase mRNAs are potential targets for RNAi against P. citri, and that recombinant TMV is an effective tool for evaluating candidate RNAi effectors in plants.

Effect of wheat cultivars on aphids and their predator populations

th week of February was found to be very favourable for aphids in wheat fields in the study area. The highest and lowest populations of coccinellid predators (all species) were recorded on TW0135 and 99T007 cultivars, respectively. The highest population of coccinellid predators was recorded during the 3 rd week of February. We observed a significant synchronization between aphids and coccinellids populations. It is concluded from the study that as INQLAB-91 is resistant to the attack of aphid’s population, this cultivar should be promoted in the areas of high aphid infestation. The populations of coccinellids follow the aphid’s population and coccinellids can be important biological control agents of aphids and can be imported tool for IPM programme in the study area.

Botanicals, selective insecticides, and predators to control Diaphorina citri (Hemiptera: Liviidae) in citrus orchards

The Asian citrus psyllid (ACP) Diaphorina citri Kuwayama vectors pathogens that cause huanglongbing (HLB) or citrus greening devastating and economically important disease present in most citrus growing regions. Young citrus shoots are required for psyllid reproduction and development. During winter citrus trees produce little or no new growth. Overwintering adults reproduce in spring on newly emerging shoots also attractive to other pests and beneficial insects. Botanicals and relatively selective insecticides could help to conserve beneficial insects and reduce pest resistance to insecticides. Sprays of Azadirachtin (Neem), Tropane (Datura), Spirotetramat, Spinetoram, and broad‐spectrum Imidacloprid were evaluated to control ACP in spring and summer on 10‐year‐old “Kinow” Citrus reticulata Blanco trees producing new growth. Psyllid populations were high averaging 5–9 nymphs or adults per sample before treatment application. Nymphs or adults were significantly reduced to 0.5–1.5 per sample in all treatments for 3 weeks, average 61%–83% reduction. No significant reduction in ladybeetles Adalia bipunctata, Aneglei scardoni, Cheilomenes sexmaculata, and Coccinella septempunctata was observed. Syrphids, spiders and green lacewings were reduced in treated trees except with Tropane. Studies are warranted to assess impact of these predators on ACP and interaction with insecticides. Observed reduction in ACP populations may not be enough considering its reproductive potential and role in the spread of HLB. Follow‐up sprays may be required to achieve additional suppression using rotations of different insecticides.

Wheat Crop Yield Losses Caused by the Aphids Infestation

Present study was planned to determine the yield loss in wheat crop at different dates of observation for the population of aphids. The wheat cultivar BK-2002 was sown at Arid Zone Research Institute, Bhakkar. For two different treatments viz. sprayed and un-sprayed wheat crop was compared, sprayed crop was observed with minimum aphid’s population whereas un-sprayed appeared comparatively susceptible with maximum population of aphids. Thiamethoxam (Actara®) was used as insecticide for sprayed treatment @ 25 gm/acre as recommended commercially. Last week of February was found to be very favourable for aphids in wheat fields in the study area. Third week of February was found to be the most suitable period for the bio-control agents i.e. Coccinellids in wheat crop. Positive correlation was found to exist between the population of aphids and Coccinellids among different wheat cultivars.

Assessment of Calotropis Procera Aiton and Datura alba Nees Leaves Extracts as Bio-Insecticides Against Tribolium castaneum Herbst in Stored Wheat Triticum Aestivum L.

Plant materials have been used for pest control for centuries but recently, preservation of cereals products in storage has relied upon chemical insecticides to control stored grain pests but having drawbacks of toxicity to non-target organisms, human health hazards, development of pest resistance and environmental pollution. The present study was conducted to control the serious cereal’s (wheat) stored grains pest Tribolium castaneum Herbst. Calotropi sprocera Aiton (Ak) and Datura alba (Dhatura) have been reported by many researchers as natural insecticides against stored grain pests. Five concentrations of leaf extracts of C. sprocera and D. alba (20%, 40%, 60%, 80% and 100%) were compared to see their efficiency to control Tribolium castaneum. Different parameters like repellency, growth inhibition, mortality rate, infestation/spoilage of grains, insect population and losses in grain weight were tested after application of treatments. Three months storage of wheat grains showed maximum repellency, mortality at higher concentrations of C. sprocera and D. alba, but there was less infestation/ spoilage, loss in grain weight and insect population at higher concentrations (80%,100%).

Two-Spotted Ladybeetle Adalia bipunctata L. (Coleoptera: Coccinellidae): A Commercially Available Predator to Control Asian Citrus Psyllid Diaphorina citri (Hemiptera: Liviidae).

The Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera: Liviidae) is an economically important pest of citrus because it serves as a vector of the causal pathogens of huanglongbing (HLB) also known as citrus greening disease. The increased use of insecticides for control of D. citri negatively impacts several natural enemies including some effective ladybeetle species which are not available commercially. The two-spotted ladybeetle, Adalia bipunctata (Coleoptera: Coccinellidae) is found in some crop and forest ecosystems of Asia, Europe and North America and available commercially. It is known to attack aphids and mealybugs but there are no published records of feeding on psyllids. We evaluated suitability and preference of A. bipunctata for nymphs of D. citri compared to corn leaf aphid Rhopalosiphum maidis (Hemiptera: Aphididae) a global pest of cereal crops and prey for many predaceous insects. We also compared development and reproduction of A. bipunctata on these two species with frozen eggs of the Mediterranean flour moth Ephestia kuehniella (Lepidoptera: Pyralidae) at 25°C. Initially, more D. citri than R. maidis nymphs were consumed in the no-choice tests although final consumption by larva and adult of A. bipunctata did not differ in the choice and no-choice tests. Larval development was prolonged by one day on D. citri compared to R. maidis nymphs but did not differ between either of these diets and E. kuehniella. Larval survival to adult averaged 93–100% and was not impacted by diet. Adult life span did not differ between diets although those on D. citri and R. maidis nymphs weighed less and produced fewer but more fertile eggs than on E. kuehniella eggs. Significant reduction of D. citri nymphs averaging 54% was observed in colonies caged with adult A. bipunctata on field planted citrus. R° (net reproductive rate) was least for beetles fed R. maidis, but otherwise there were no significant differences in demographic parameters. Successful feeding, development and reproductive performance of A. bipunctata suggest its usefulness as biological control agent of D. citri as well as aphid species exemplified by R. maidis.