Parasitism Behaviour of the Braconid Wasps, Coccygidium Luteum and Cotesia Icipe and their Performance on the Fall Armyworm (Spodoptera frugiperda) Larva.

Abstract

Fall armyworm is an invasive crop pest that has caused much damage to food crops since it invaded West Africa in 2016. Coccygidium luteum and Cotesia icipe were among the most promising Fall armyworm larval parasitoids scouted and identified in the West African sub-region. The study focus on making a choice on using either one, or both larval parasitoids in a Fall armyworm biological control programme in Ghana, as parasitoid populations of these species were different in East and West African sub regions. The generation time, preference, parasitism levels, and a test for competition and its effect on Fall armyworm were conducted for both parasitoid species. Coccygidium luteum recorded an average generation time of 30.1 days and maximum voltinism of 12 generations per year. Cotesia icipe recorded an average generation time of 16.9 days and maximum voltinism of 21 generations per year. Coccygidium luteum showed parasitism preference from newly emerged larva to 7 days old larva (1st to early 4th Fall armyworm larval instar). Four and five days old Fall armyworm larva (2nd and early 3rd larval instar) was ideal for higher parasitism, with a lower percentage mortality and higher percentage adult parasitoid emergence. Cotesia icipe showed parasitism preference from newly emerged larva to 4 days old larva (1st to 2nd Fall armyworm larval instar). One day, and two days old Fall armyworm larva (1st Larval instar) was ideal for higher parasitism, with lower percentage mortality and higher percentage adult parasitoid emergence. C. luteum recorded an average of 30 parasitism daily after two hours exposure (59.5 %), and a total of 149 parasitism in five days. C. icipe recorded an average of 24 parasitism daily, after two hours exposure (44. 7%), and a total of 112 in five days. Competition was found to exist between both parasitoid species as they exploit the same host larva with an overlapping preference range, but the competition works synergistically in controlling Fall armyworm through increase in Fall armyworm mortality. C. luteum attacked largely day 0 to 7 days old Fall armyworm larva (1st to early 4th instar). C. icipe attacked day 0-4 day-old larva (1st to 2nd instar). Older Fall armyworm larva (5th instar and above) expressed a physical aggression defensive behaviour.