Friends or foes? Population dynamics of beneficial and detrimental aerial arthropods under Conservation Agriculture

Arthropod pest control is one of the most critical agronomic practices in cereal-based cropping systems. Cropping systems that preserve or promote biological pest control agents are more desirable. Data collected from a long-term trial at the Monze Farmer Training Centre (MFTC) from 2009 to 2012 was used to compare effects of different Conservation Agriculture (CA) systems with conventional practices (CP) on arthropod species diversity and populations with specific emphasis on beneficial and detrimental aerial arthropods. Up to 13 arthropod orders comprising of 40 species were identified in the cropping systems and their population density differed in years and cropping systems. Higher diversity was observed in CA systems in all years based on the Shannon-Weiner indices ranging from 0.4 to 2. However, a CP system with no rotations (CP-M) showed comparable results in the year with low rainfall. Community evenness increased in the same year with a value of 0.46. More beneficial and detrimental arthropods were recorded in a CA system with a three-year rotation of maize, cotton and sunnhemp reaching up to 9533 individuals ha(-1). The CP-M recorded the highest increase in detrimental arthropods from 2009 to 2012. A canonical correspondence analysis did not show a clear-cut association of both CA and CP systems with either beneficial or detrimental arthropods. However, associations were more driven by seasonal effects. Reduced soil disturbance, crop residue retention and crop diversity in CA systems preferentially attracted beneficial arthropods while preserving existing favourable arthropods. Conventional tillage systems often disturbed arthropod habitats, disrupted their life cycles leading to lower biological activity. Increased biodiversSity from CA systems may therefore support biological control.