Host selection and survival of the parasitoid Encarsia formosa on greenhouse whitefly, Trialeurodes vaporariorum, in the presence of hosts infected with the fungus Aschersonia aleyrodis

Abstract

Successful control of greenhouse whitefly may be achieved by complementary activity of the parasitoid Encarsia formosa and the fungus Aschersonia aleyrodis. One way to obtain an additive mortality effect of both entomopathogen and parasitoid would be achieved by the selection of healthy hosts by the parasitoid and rejection of fungus‐infected hosts. Third and fourth instar larvae of Trialeurodes vaporariorum which had been treated with a spore suspension of A. aleyrodis 0, 4, 7, 10 or 14 days beforehand, were presented to female parasitoids. The parasitoids adopted the oviposition posture on untreated hosts as well as on treated hosts, irrespective of the different stages of infection in the hosts. However, significantly more hosts were parasitized by E. formosa in the control treatment than in the fungal treatment. The parasitoids offered treated hosts, showed rejection behaviour after probing on hosts showing detectable signs of infection (containing hyphal bodies or mycelium in the haemolymph). For instance, when hosts were offered seven days after spore treatment, the parasitoids showed an oviposition posture on a total of 83 (95.4%) out of 87 infected larvae, but laid only 4 eggs (4.6%). In contrast, on 48 (94.1%) out of 51 noninfected (or showing no detectable signs of infection) hosts an oviposition posture was adopted and 40 eggs (78.4%) were found after dissection. When infected hosts were encountered the oviposition posture lasted less than 1′40″ while rejection of non‐infected hosts occurred after more than 1′40″. Other experiments were carried out offering treated hosts for 24 h to the parasitoids. The hosts were dissected afterwards. Again, significantly more eggs were laid in the non‐infected hosts. When hosts were parasitized shortly after fungal spore treatment they were colonized by the fungus and the parasitoids did not develop. Transmission of the entomopathogen after probing infected hosts was observed to a limited extent. In conclusion, A. aleyrodis and E. formosa can be used together in a glasshouse situation. The parasitoid will be most effective when introduced more than seven days after application of A. aleyrodis, because from that time onwards it is able to detect and reject fungus‐infected hosts.

Combined effects of the entomopathogenic fungus, Paecilomyces fumosoroseus Apopka-97, and the generalist predator, Dicyphus hesperus, on whitefly populations

“…Phloem feeding by large populations of T. vaporariorum retards plant vigor and the production of copious amounts of honeydew on leaves and fruits stimulates the growth of sooty mould fungi. Large amounts of fungal growth inhibit the photosynthetic processes of leaves and leads to downgrading of the fruit (Osborne and Landa, 1992;Fransen and van Lenteren, 1993;Poprawski et al, 1998). Many studies have demonstrated the ability of various natural enemies to suppress T. vaporariorum populations, including an aphelinid parasitoid (van Lenteren et al, 1996(van Lenteren et al, , 1997, hemipteran predators (Albajes et al, 1996;Sampson and King, 1996;McGregor et al, 1999) and entomopathogenic fungi (Osborne and Landa, 1992;Poprawski et al, 2000;Meekes et al, 2002).…”

Whitefly control in cut gerbera: is it possible to control Trialeurodes vaporariorum with Encarsia formosa?

“…In all cases, growers noted that T. vaporariorum was the most important pest insect on cut gerbera. Whitefly nymphs and adults cause direct damage by piercing and sucking, and excreting large amounts of honeydew that promote development of sooty mold fungi and, thus, impair photosynthesis (Byrne et al 1990;Osborne and Landa 1992;Fransen and van Lenteren 1993;Poprawski et al 1998).…”

Influence of plant resistance at the third trophic level: interactions between parasitoids and entomopathogenic fungi of cereal aphids

“…He de®ned two potential interactions: (1) intrahost interactions, during ontogenetic development of the natural enemies within a shared host; and (2) extra-host interactions, which take place outside the host and involve eventual transmission of the pathogen by the parasitoids. Intra-host interactions between parasitoids and fungi are asymmetrical and determined by the timing of parasitoid oviposition and fungal infection (Powell et al 1986;Fransen and van Lenteren 1993). The fungus usually outcompetes the parasitoid unless the development of the latter begins several days before fungal infection.…”

“…The fungus usually outcompetes the parasitoid unless the development of the latter begins several days before fungal infection. The eect of the relative timing of the attacks of natural enemies is known as the priority eect (Powell et al 1986;Fransen and van Lenteren 1993). In relation to extrahost interactions, entomopathogenic fungi are dependent upon abiotic (e.g.…”