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

Abstract

We investigated the impact of inundative releases of the parasitoid, Encarsia formosa Gahan (Hymenoptera: Aphelinidae), for control of greenhouse whitefly, Trialeurodes vaporariorum (Westwood), on cut gerbera (Gerbera jamesonii L.) under controlled greenhouse conditions. Experimental units consisted of ten plants covered and separated from other units by gauze tents. We assessed three release rates of the aphelinid parasitoid: a 7-week experiment with a standard release rate (10 m -2 /14 days), and a subsequent 3-month trial with high (100 m -2 /week) and very high (1,000 m -2 /week) release rates. Experimental units without release of parasitoids served as control treatment. Gerbera plants were infested initially with 50-100 juvenile and 50-70 adult whiteflies in the first experiment, and in the second experiment with less than 50 juveniles per plant and 50-70 adults. Whitefly and parasitoid population density were assessed in weekly intervals using infestation and activity categories. Results show that parasitized whiteflies were present in all treatments within 2 weeks after initial release. Unfortunately, it was not possible to control whiteflies with standard release rates of E. formosa. Although parasitism rates slightly increased, the effect on whitefly populations was negligible. Large amounts of honeydew and growth of sooty mold fungi caused the termination of the first experiment. In a second experiment, E. formosa was tested at 10-100 times higher release densities. In contrast to the first experiment, whitefly densities increased steadily during the first 8 weeks, but remained constant until the end of the experiment in both treatments. Parasitism by E. formosa reached its maximum after 8 weeks. We discuss possible reasons for the low efficiency of E. formosa as a whitefly antagonist in greenhouse production of gerbera.

A Scouting Method for Estimating Insect Populations in an Encarsia formosa (Hymenoptera: Aphelinidae) Mass Rearing System

“…The efficiency ratio stablished in this work (Fig 4) shows that as the number of E. formosa released in a production cycle increased, the number of E. formosa adults that were produced diminished, suggesting that the optimal number should be approximately 7000 in a weekly production batch. Similar results were reported by Berndt & Meyhöfer (2007), which analyzed the control efficiency of E. formosa released at high densities (1.000) over a T. vaporariorum population in Gerbera. According to the authors, the use of this high E. formosa density caused a decrease in the rate of parasitism, which was possibly related to the parasitoid selection process for oviposition and/or predation (i.e., host-feeding) of the prey.…”

Whitefly‐induced tomato volatiles mediate host habitat location of the parasitic wasp Encarsia formosa, and enhance its efficacy as a bio‐control agent

“…5). 25,26 Once Trialeurodes vaporariorum abundance substantially increases, the whitefly and parasitoid populations may exhibit stable dynamics because whitefly patches may not be fully eliminated by the parasitoid 23 . Thus, the density of whitefly populations at the time when E. formosa is released greatly affects the efficacy of E. formosa as a control agent 24 .…”

“…To enhance the parasitism rates by E. formosa , the use of an increased release density of parasitoids was attempted, but failed to reach higher parasitism rates 24 . Until now, most efforts to use E. formosa to control Trialeurodes vaporariorum and B. tabaci in glasshouses have been characterized by low efficiency and discontinuity 23–27 . Recently, Zhang et al 20 .…”

“…Because E. formosa has the potential to control the whiteflies Trialeurodes vaporariorum and B. tabaci on tomatoes, its biology and behavior have been intensively studied in order to identify factors that contribute to its success as a biological control agent 15–22 . It has been reported that the initial density of whiteflies, frequency of parasitoid release, and glasshouse temperature strongly influenced the efficacy of E. formosa wasps as a whitefly antagonist in glasshouses 23,24 . To enhance the parasitism rates by E. formosa , the use of an increased release density of parasitoids was attempted, but failed to reach higher parasitism rates 24 .…”

Detection of a related difference in efficacy of azadirachtin treatments for the control of whiteflies on Gerbera jamesonii by testing for interactions in generalised linear models

“…Indirect damage is caused by the development of sooty mould fungi, which decrease assimilation efficiency in considerable measure. Furthermore, viruses can be transmitted by whiteflies 1–4. To achieve a regulation of the whitefly by insecticides is difficult, because the effectiveness of the chemical insecticides decreases as resistance builds up.…”