Host plant suitability and efficacy of selected insecticides for control of Tuta absoluta (Lepidoptera : Gelechiidae)

Abstract

Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is an oligophagous species, native to the neotropics of South America and is one of the most serious pests of tomato globally. Tuta absoluta develops on various cultivated and non-cultivated Solanaceae plants. The spread and invasive nature of T. absoluta can be facilitated by the permanent availability of alternative host plants, including weeds, in the absence of tomato. This information is important in terms of integrated management strategies for T. absoluta, to determine which plants serve as host reservoirs or can be used as trap plants. Insecticide application is the main control strategy worldwide. Control failure of several insecticides as a result of resistance has, however, been reported from various countries. The aim of this study was to evaluate certain plant species, regarded as weeds in South Africa, for the ovipositional preference of T. absoluta moths and suitability for development of larvae, and to estimate the baseline susceptibility of T. absoluta to selected insecticides. Feeding damage to, and preference of T. absoluta larvae for Chenopodium pumilio (Amaranthaceae), Chenopodium album (Amaranthaceae), Ipomoea purpurea (Convolvulaceae), Solanum elaeagnifolium (Solanaceae), Datura ferox (Solanaceae), as well as tomato were evaluated in no-, two- and multi-choice tests under laboratory conditions. Tomato was the most preferred in no-, two- and multi-choice feeding tests and larvae also consumed significantly more leaf material of tomato plants than of weeds. The same plant species were evaluated in oviposition preference tests. Eggs were oviposited only on tomato and C. pumilio in no-choice tests. Neonate larvae did, however, not feed on C. pumilio and died soon after hatching. This plant species could therefore be investigated further as a possible dead-end trap plant. Tuta absoluta did not feed or oviposit on D. ferox. Second-instar larvae were able to feed on C. pumilio, C. album, I. purpurea and S. elaeagnifolium in the preference tests. Completion of the life cycle and reproduction by the following generation should be investigated to determine the host status of these species, and to determine if they can serve as reservoir plants where T. absoluta can establish. Baseline susceptibility of T. absoluta populations from three areas to chlorantraniliprole, spinosad and lambda-cyhalothrin was estimated. All three populations were susceptible to chlorantraniliprole and spinosad, but showed low levels of susceptibility to lambda-cyhalothrin. It is therefore anticipated that chlorantraniliprole and spinosad will both provide effective control under field conditions, with the recommended dosage rates >21 fold and >80 fold higher than the estimated LC80 values, respectively. Since this was the first attempt in South Africa to determine baseline susceptibility and possible resistance to insecticides, the baseline estimates will be used in future resistance monitoring of T. absoluta to insecticides in the country.