Biological effects of three Annona species on Callosobruchus chinensis: A green alternative for storage pest management

Abstract

Plants have been known as a rich source of bioactive chemicals. These have been exploited in insect-pest management strategies as repellents, feeding deterrents, ovipositional deterrents and in many other ways in the biology of insects. The possible use of Annona species as eco-friendly alternatives to synthetic insecticides for the management of Callasobrucus chinensis in legumes was investigated from this perspective.  In the present study, methanol extracts of leaves of Annona squamosa (Sugar apple), A. reticulata (Custard apple), and A. glabra (Pond apple) were evaluated to determine their effects on the oviposition, egg incubation and hatchability of C. chinensis. The effect of leaf extracts on the viability of cowpea seeds was also determined. Three doses (2.5, 7.5 and 12.5g/l) of leaf extracts were used in all tests.

All the extracts tested resulted in significant reduction in oviposition in females. This reduction was dose-dependent and increased with the increase of dosage. Extracts of A. squamosa induced significantly the highest oviposition deterrence of 49.4% in the insects at the highest dose of 12.5g/l. A. reticulata (42.5%) and A. glabra (32.3%) on the other hand caused respectively lower deterrence. No deterrence of oviposition (0.0%) was observed with the control. In contrast, egg hatchability decreased with the increase of the dosage of extracts. A. squamosa at the highest dose evoked the lowest percentage egg hatch (35.2%) while 96.4% eggs hatch was observed with the control. Egg hatchabilty caused by A. reticulata extract at the same dose was 70.3% which was twice as much observed with A. squamosa. Furthermore, incubation period of eggs also increased with time and dose. In comparison to the control (4.0 days), the highest incubation period was recorded from eggs treated with A. glabra at the dose of 12.5g/l (7.7 days) followed by A. squamosa (6.9 days). None of the plant extracts elicited any adverse effects on the germination capability (viability) of cowpea seeds which varied between 99-100%.

The overall results of the study indicate that all three Annona species have a positive impact on the management of this beetle. Moreover, A. squamosa could be considered as the most effective compared to the other two species. As all three plant species tested are locally available, the outcome of this study may certainly help in paving the way for their usage against post-harvest pests.