Studies On Ecology,Mating Behaviour,Responses To Neonicotinoid Insecticides And Heat Shock Of Cotton Mealybug Phenacoccus Solenopsis(Tinsley)(Hemiptera:Pseudococcidae)

Cotton mealybug,Phenacoccus solenopsis Tinsley(Hemiptera:Pseudococcidae)was first described by Tinsley(1898)from USA.This pest spread rapidly throughout the American region,and currently it is distributed over a wide range of agro-ecological zones in at least 24 countries in the world.This pest is an invasive and highly polyphagous pest,its damage was recorded on more than 200 plants that are belonging to 55 plant families.It causes heavy losses in cotton and ornamental plants in many Asian countries,including China,India and Pakistan.At the same time,the host range of P.solenopsis is also rapidly expanding.Tomato has become one of its more common host plants.Its nymphs and adults produced more honeydew on the tomato leaves than on cotton that led to reductions in leaf photosynthesis and respiration because of sooty mold,and finally it led to death of plant.The biological characteristics of this notorious pest have been reported by many scientists,especially on cotton,but some results were controversial.Meanwhile,some characteristics have not been studied before.Therefore,in this thesis,I carried out different experiments by utilizing tomato as host plant to assess the influences of constant and fluctuating temperature,to clear its reproductive attributes,to evaluate the effects of delayed mating on reproductive parameters,to investigate the lethal effects of two neonicotinoids,acetamiprid and imidacloprid,and effects of their sublethal dosage on antioxidant enzymes and feeding behaviors.I also carried out experiment to investigate the influences of induced heat shock on its survival,feeding behavior and antioxidant enzymes.I obtained the results as following.The effects of temperature on development,survival,reproduction parameters and longevity of the cotton mealybug,Phenacoccus solenopsis Tinsley,assessed in laboratory under 5 constant temperatures ranging from 20 to 35 ℃ and five fluctuating temperatures ranging from 15 to 40 ℃.The results showed that at constant temperature,nymphal development duration,preoviposition period,oviposition period,fecundity and adult longevity of both sexes were reduced significantly with increasing temperature until 30 ℃,but development duration for the 3rd female nymph and female adult longevity at 35 ℃ were longer than that at 30 ℃,and no male emerged out from puparium at this highest temperature.As compared with corresponding mean constant temperature,in generally,fluctuating temperature significantly accelerate the nymphal development,prolonged preoviposition period,shorted oviposition period,reduced fecundity,lowed survival rate of nymphs and decreased adult longevity for both sexes.The results suggest that it should be prudent when applying the obtained results under constant temperatures under laboratory condition.Since the controversial results about the reproductive mode of this pest were existed in the references,in this part,reproductive attributes,including the reproductive mode,male’s mating capacity,influence of female’s age and density on male’s mating capacity,as well as the influence of copulation on female’s longevity,were investigated under the laboratory condition.The results demonstrated that P,solenopsis reproduced sexually.Males mated 1-2 times in one day and 3-6 times in their lifetime,and did not show mating preference for female age or density.Although a few unmated females produced ovisacs,while they neither produced eggs nor gave birth any crawlers in the ovisacs.Unmated females significantly lived for longer durations than the mated ones.Sexual reproduction with short lived males may imply great potential for control practices that target males;for example,application of sex pheromone for trapping and killing male,or spraying of chemicals during the time of male activity,may be an effective practice for the management of this pest.Effects of delayed mating were investigated in laboratory on the male mating success,female reproductive performance and both male and female adult longevity of Phenacoccus solenopsis Tinsley.The results showed that male-only delayed mating increased female prereproductive period(the time between emergence and producing offspring)and male longevity,and reduced the oviposition period,fecundity and male’s copulatory capacity,but not affect the preoviposition period(the time between mating and producing offspring)and female longevity.Conversely,female-only delayed mating did not change male’s mating success and male longevity.Female-only delayed mating showed a gradual decreasing trend in prereproductive period but a gradual prolonging trend in preoviposition period and female longevity,female oviposition period did not change until female age was more than 34 days and female fecundity kept unvaried until the female age was more than 26 days.Both sexes’delayed mating greatly reduced prereproductive period,oviposition period,fecundity,and male copulation capacity but greatly increased preoviposition period and both male and female longevity.These results suggest that mating disturbing techniques,such as application of sex pheromones,will be very useful ways to control the population of P.solenopsisAcetamiprid and imidacloprid are two important neonicotinoid insecticides that are widely utilized under field conditions for the management of sucking insect pests,including the cotton mealybug Phenacoccus solenopsis Tinsley(Hemiptera:Pseudococcidae).Although some information is available regarding their lethal effects,nothing is currently known about the sublethal effects of these insecticides.Therefore,I performed a series of experiments to test the lethal and sublethal effects of these chemicals on oviposition duration,fecundity and antioxidant enzymes.I also assessed sublethal effects on feeding behavior using the electrical penetration graph(EPG)technique.The results of this study reveal that acetamiprid toxicity was higher than imidacloprid.When applied at sublethal dosages,these chemicals significantly reduced oviposition duration and fecundity;as compared to control,CAT activity was increased in response all dosages of acetamiprid and all dosages of imidacloprid(except LC75),POD activity was decreased in response to all dosages of both chemicals;however,SOD activity was increased in response to all dosages of acetamiprid,and reduced in response to all dosages of imidacloprid except LC25.Treatments with these two insecticides significantly prolonged non-probing duration,and reduced phloem and xylem feeding activities when compared to adults exposed to just water.No significant differences were detected in all waveform durations and events when adults previously exposed to foliage treated with each of these two insecticides were compared.The results obtained in this study,therefore,suggest that both insecticides are able to protect crops from mealybug damage not only by directly killing these pests but also by indirectly reducing their fecundity and inhibiting feeding behaviors when applied at sublethal dosages.Temperature is an important abiotic environmental factor,and is responsible for various kinds of behavioral and physiological changes in the living organisms.Induced heat shock is associated with feeding behaviour and reactive oxygen species(ROS)generation that causes oxidative damage.In this thesis,I investigated the sublethal effects of heat shock on the feeding behaviours of cotton mealybug,Phenacoccus solenopsis(Tinsley)(Hemiptera:Pseudococcidae),particularly phloem and xylem functionality as well as the impact upon antioxidant enzymes,including CAT,SOD and POD in P.solenopsis female adults.The results showed that heat shock altered the P.solenopsis feeding preference as it increased the xylem feeding duration and percentage of adults producing xylem feeding whilst reduced the phloem feeding duration and percentage of adults producing phloem feeding of P.solenopsis Tinsley.Similarly it altered the antioxidant enzyme activity,an increase of CAT,SOD and POD activities were noticed in response to highest intensity of heat shock while a reduction of the CAT and SOD activity were noticed in response to lowest intensity of heat shock compared to control(30 ℃).These results suggest that heat shock may result in loss of body water and induce oxidative stress in P.solenopsis.However,antioxidant enzymes play a significant role in overcoming the oxidative damage.Overall,the findings in this thesis will provide important information for further study on the effect of constant and fluctuating temperature,effect of insecticides and heat shock on the P.sole,nopsis.The results will be helpful to understand the population dynamics of P.solenopsis under the constant and fluctuating temperature,and will provide effective management practices at the lethal and sublethal doses of acetamiprid and imidacloprid.Delayed mating results will proved to be very effective for the management of P.solenopsis after using mating disturbing techniques,such as sex pheromones.