A compared evaluation of Encarsia formosa Gahan and Encarsia pergandiella Howard (Hymenoptera: Aphelinidae) as biological control agents of Trialeurodes vaporariorum (Westwood) (Homoptera: Aleyrodidae) on tomato under greenhouse in southern Italy

A comparative evaluation of Encarsia formosa Gahan and Encarsia pergandiella Howard (Hymenoptera: Aphelinidae) as biological control agents of Trialeurodes vaporariorum (Westwood) (Homoptera: Aleyrodidae) was carried out on tomato under greenhouse in southern Italy (Campania). In a structure of 1330 m2 (35 x 38 m), divided in 5 tunnels tomato plants cv Arletta were transplanted on 23.2.1999. Parasitoids were released weekly from 19.5.99 (harvest beginning) to 16.6.99 in 3 tunnels (tunnel l, 3 and 5), each one alternated with a control tunnel (tunnel 2 and 4) where no parasitoids were released. Three combinations of releasing were performed: E. pergandiella (tunnel 1), E. pergandiella + E. formosa (tunnel 3) and E. formosa (tunnel 5). Pupal case density increased progressively into the five tunnels from 0.02 to 5.86 pupal cases/leaflet throughout the harvest time without reaching the intervention threshold. No significant damage on fruits caused by honeydew and sooty mould was observed. The percentage of parasitization increased regularly in all tunnels. On 7.7.99, after 1.5 months from the first release, it ranged from 17.73 per cent to 36.75 per cent, doubling after another 21 days (on 28.7.99) when the parasitization ranged from 57.06 per cent to 70.63 per cent. Between the two species inoculated, E. pergandiella was the most abundant and spread in each tunnel. E. formosa substantially spread into the tunnels where it was inoculated, suffering the competition from E. pergandiella. Into the tunnel 5, E. formosa reached the 49.63 per cent of total parasitization on 28.7.99. Into the tunnel 3, where the parasitoids were released together, the competition performed by E. pergandiella was strongE. formosa activity decreased from 13.04 per cent (30.6.99) to 0 per cent (28.7.99) of the total parasitization. Results achieved in the present work point out that, at least in greenhouse areas of southern Italy where natural populations of E. pergandiella are widespread, an effective control of the whitefly can be obtained reinforcing the activity of natural E. pergandiella populations by means of multiple inoculations of the same parasitoid as soon as whiteflies infest the crop. The dominance of E. pergandiella on E. formosa seems linked not only to the male hyperparasitism but also to a better adaptation of the first species to the climatic and growing conditions