Responsibility of Certain Biotic Factors for Management Populations of Brevicoryne brassicae L in Cabbage fields

Abstract

This work was carried out at the experimental farm of the Faculty of Agriculture, Assiut University during the 2017-2018 and 2018-2019 cabbage growing seasons. Evaluation of the seasonal abundance of the cabbage aphid Brevicoryne brassicae L in cabbage fields and responsibility of certain biotic factors for managing populations of this insect pest was the cornerstone of this investigation. Cabbage aphid, B. brassicae was found to be active on cabbage plantations and recorded in low numbers (99.71 individuals / 12.5 Cm 2 / leaf / infested plant) at the beginnings of the season (November) with gradual increase until harvesting. Three amongst the six evaluated cabbage cultivars and/or hybrids were appeared as susceptible (S) and harbored so high numbers of the pest. However, the remaining cultivars showed some sort of resistance to this insect pest. The local cultivar (Ganzory) harbored the least aphid numbers and appeared as moderately resistant (MR) cultivar. This finding could be attributed to the antixenosis and/or antibiosis phenomena presented by this local cultivar. Proteins and amino acid contents showed a highly significant positive correlation (r) with B. brassicae populations, however, chlorophyll showed highly significant negative (r). The obtained data reflect the role of the cabbage aphid parasitoid Diaeretiella rapae (McIntosh) to manage B. brassicae populations. Mummified aphids (parasitism rate) before harvesting were found to be equal 6.16 fold of that recorded before ripening stages. High percentages of D. rapae were succeeded to emerge from the mummified B. brassicae with diverse extrusion rates. Multiple increases were recorded on the percentages of infested plants when cabbage undergo toward ripening at the 9 th stage till harvesting. No or less existence of unmarketable plants (through the periods of the low infestation) before cup formation and/or plant ripening period was recorded. So, it can be concluded that cabbage cultivar, plant age, and stage in addition to plant metabolites combined with the naturally occurring biological control agent (Aphid parasitoid) can be affected and manage the population trend of cabbage aphid B. brassicae infesting cabbage in the field.