Abstract:
Cotton stainer, Dysdercus superstitiosus is a hemimetabolous bug which is a general pest of many crops such as seeds of cotton and citrus plants and cause considerable damages to them. The chemicals used as control of insect pests’ population endangers human health and the environment due to their toxicity, thus creating a need for safer alternatives, to which botanicals are advocated for. It is along this background that this study assessed the sterility efficacy of extracts of Syzygium aromaticum (Clove) and Plumbago zeylanica (Leadwort) on Dysdercus superstitiosus using the life history, total development period and alterations of the histology of the bug’s reproductive organs as indices. Bioassays included various concentrations of the plant extracts (2%, 4%, 8%, and 10%) and acetic acid (0.2%, 0.4%, 0.8%, and 1.0%) which served as a standard control. Each experiment was replicated three times. Eggs, immature and adult insects were topically administered with the various concentrations of the extracts. The data obtained were subjected to both One-Way and Two-Way Analysis of Variance (ANOVA) tests as appropriate. Tukey’s multiple comparisons were applied to measure the level of difference between control and experimental groups. Results were considered significant at p<0.05.The results revealed that the two plant extracts caused significant mortalities (p<0.05) on the insects when compared with control with Plumbago zeylanica having higher efficacy than Syzygium aromaticum. At 10% concentration of Syzygium aromaticum extract, just 28.3% of the eggs hatched (p<0.05) and 48.6% mortality, whereas, at the same concentration of Plumbago zeylanica extract, only 2% of the eggs hatched (p<0.05) and there was 100% mortality. The results of this study therefore showed that the two extracts have suppressing ability on the insects’ population by inhibiting egg hatchability and causing histological damages on the male and female gonads, thus suggesting that they may be promising male sterilising agents. Plumbago zeylanica shows more effective insect growth regulatory effect than Syzygium aromaticum and presents itself a potential agent in field population control of D. superstitiosus.
