Monitoring of Aphid Fauna in Passionfruit Orchards in Kenya

Abstract

Passionfruit woodiness disease viral pathogens limit passionfruit production and are non-persistently transmitted by aphid vectors. The study was conducted to identify aphid species and assess the population dynamics of potential vectors in the orchards for purposes of developing viral disease management tactics. Field trials laid out in a randomized complete block design with four replicates, were conducted in Kabete and Embu and aphid populations monitored weekly in passionfruit orchards for a year using yellow water pan traps under natural conditions. Aphid transmission tests using commonly found aphids Aphis gosypii, A. fabae, Brevicoryne brassicae, Ropalosiphum maidis, and Sitobion avenae and a CABMV isolate from the field were also carried out in the greenhouse. These tests would establish the ability of the aphid species to transmit CABMV. Twelve species of aphids were captured but the most abundant were Aphis gosypii, Ropalosiphum maidis, Acyrthosiphon pisum and Brevicoryne brassicae accounting for 97% and 95 % of the total aphids collected in Embu and Kabete, respectively. The species diversity was rich and abundant at 0.79 and 0.7 for Kabete and Embu, respectively. The aphid population in Kabete (8000) was significantly (p< 0.05) higher than that collected in Embu (2900) whereas the population collected during the long rains season was significantly (p<0.05) higher than that which was collected in the short rains. Individual species populations were higher in Kabete than in Embu but only A. gosypii, Macrosiphum euphorbiae, Myzus persicaeand R. maidis had significantly (p<0.05) higher populations in Kabete. About 70% of the total aphids were collected during the peak period in both sites indicating greatest aphid dispersal and flight activity. The aphids were present in the orchards throughout the year with one major seasonal peak in June, a time period when food crops and other vegetation such as weeds grow vigorously. The occurrence of aphids in the orchards throughout the year with the peak population density coinciding with the cropping season has serious implications in the management of the pest and spread of viral diseases of passionfruit.