Evaluation of the Functional Response of Seven Spotted Lady Bird Beetle Coccinella septumpunctata (Coleoptera: Coccinellidae) on Five Varying Densities of Bemisia tabaci (Homoptera: Aleyrodidae) Population under Controlled Laboratory Conditions

Abstract

Bemisia tabaci is a cosmopolitan polyphagous insect undermining the productivity of  a wide range of crops including but not limited to horticulture, ornamental and vegetable crops. The management of B.tabaci  has been dominated by the use of broad-spectrum insecticides, though having the unique feature of reducing pest population below action threshold and economic injury level, their usage is however characterized with side effects including but not limited to environmental degradation and development of resistant genes in insects. The use of natural enemies (biological control) is considered more sustainable and viable option, environmentally friendly and poses no risk to users. Among the numerous biological control opportunities, the use of coccinellid beetles potentially proves to be quite promising and are abundantly found in insect infested vegetable fields.  The ability of natural enemies as effective biological control agents is highly vested in their respond to density of preys density-dependent which can be measured in terms of their functional responses focusing on instantaneous search rates (a) and handling time (Th) as distinct and invaluable parameters. A bioassay cage experiment under laboratory conditions was   carried out to evaluate the functional response of seven spotted lady bird beetle   C. septumpuntata late 4^th instars, male and female adults respectively on varying densities of B. tabaci eggs, 2^nd and 3^rd instars. The results were normalized and nature of response curves of C. septempartite on these prey densities were characterized and determined as Type II functional response.  The response curves monotonically declined with increased in pest density for the 4^th instars , female and male adults when fed on 2^nd instar larvae with  female adults showing  the highest instantaneous search rate 0.54 and lowest handling time 0.19  and maximum consumption of 10.95 prey^-1hr^-1  strongly indicating that  the female beetles showed potential attributes  as ideal biological control candidate compare to the male  and late 4^th instar counterparts  when fed on the 2^nd and 3^rd instars.  However, when beetles  were offered with B. tabaci eggs , the 4^th instars demonstrated  least handling time  0.73  and higher attack rate 2.57 than the female and male counterpart correspondingly showing the  highest satiation threshold  32.87 prey^-1hr^-1.Though the beetle  demonstrated promising potential as an ideal candidate based on current laboratory findings providing  insight on the possibility  for  mass rearing and subsequent   utilization in   biological control programs of agricultural pests , there is however need for further investigation under greenhouse and field scenarios. Meanwhile, the prospect of C. septumpunctata as an ideal biological control candidate on B. tabaci population is discussed.