The potential of Paranosema (Nosema) lucustae (Microsporidia: Nosematidae) and its combination with Metarhizium anisopliae var. acridum (Deuteromycotina: Hyphomycetes) for the control of locusts and grasshoppers in West Africa Additivity and synergistic effects biological control density reduction grasshoppers Metarhizium anisopliae Paranosema locustae vertical transmission