Interactions between the Entomopathogenic Fungus Metarhizium anisopliae ICIPE 20 and the Endoparasitoid Dolichogenidea gelechiidivoris, and Implications for Combined Biocontrol of Tuta absoluta.

The Integrated Pest Management (IPM) approach have been widely promoted and used for the management of native and invasive pests, while the use of various components of the IPM can have a synergetic, additive, or antagonistic effect on each other; this study evaluated the susceptibility of Dolichogenidea gelechiidivoris (Marsh) (Hymenoptera: Braconidae), to the Metarhizium anisopliae (Metschnikoff) ICIPE 20 through direct and indirect infection approaches. The effect of fungus on parasitoid longevity, survival of parasitized-larvae, preference of the parasitoid to fungal treated and untreated larvae, and percent parasitism of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) under different infection scenarios were assessed. The direct application of dry conidia to the parasitoid prior to exposure to the host, reduced D. gelechiidivoris longevity, though the infected female wasps still yielded high parasitism (over 70%). Infecting the parasitized larvae at different ages led to a respective reduction of parasitoid emergence by 35% and 23% for infection at 1 and 5 days post-parasitisation. Exposure of healthy-D. gelechiidivoris adults to a plant-sprayed with fungus did not affect their longevity, and no discriminatory host selection was observed. The highest mortality (~80%) of T. absoluta was achieved when D. gelechiidivoris and M. anisopliae ICIPE 20 were used in combination, indicating an additive impact on the target pest; however, field validation can shed more light on this outcome.

Can the Combined Use of the Mirid Predator Nesidiocoris tenuis and a Braconid Larval Endoparasitoid Dolichogenidea gelechiidivoris Improve the Biological Control of Tuta absoluta?

The koinobiont solitary larval endoparasitoid Dolichogenidea gelechiidivoris (Marsh) (Syn.: Apanteles gelechiidivoris) (Hymenoptera: Braconidae) and the predatory bug Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) are important natural enemies of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), a serious pest of tomato. Although N. tenuis preferentially feeds on T.absoluta eggs, it is also recorded as a predator of first and second instar larval stages. Dolichogenidea gelechiidivoris preferentially seeks these early larval stages of T. absoluta for oviposition. The occurrence of intraguild predation between N. tenuis and D. gelechiidivoris and the consequences on the oviposition performance of D. gelechiidivoris were investigated in the laboratory. Regardless of the manner of introduction (i.e., the sequence of combinations with D. gelechiidivoris) or density (i.e., number of N. tenuis combined with D. gelechiidivoris), the presence of N. tenuis did not affect the oviposition performance of D. gelechiidivoris or the parasitoid's progeny. Combination assays revealed that the efficacy of the combined use of N. tenuis and D. gelechiidivoris in controlling T. absoluta populations was significantly higher than that of either natural enemy alone. Our results highlight the potential of combining mirid predators and koinobiont larval endoparasitoids to control T. absoluta. The findings further contribute to data supporting the release of D. gelechiidivoris in tomato agroecosystems for the control of T. absoluta in Africa, where N. tenuis is widespread and abundant.

The pest kill rate of thirteen natural enemies as aggregate evaluation criterion of their biological control potential of Tuta absoluta.

Ecologists study how populations are regulated, while scientists studying biological pest control apply population regulation processes to reduce numbers of harmful organisms: an organism (a natural enemy) is used to reduce the population density of another organism (a pest). Finding an effective biological control agent among the tens to hundreds of natural enemies of a pest is a daunting task. Evaluation criteria help in a first selection to remove clearly ineffective or risky species from the list of candidates. Next, we propose to use an aggregate evaluation criterion, the pest kill rate, to compare the pest population reduction capacity of species not eliminated during the first selection. The pest kill rate is the average daily lifetime killing of the pest by the natural enemy under consideration. Pest kill rates of six species of predators and seven species of parasitoids of Tuta absoluta were calculated and compared. Several natural enemies had pest kill rates that were too low to be able to theoretically reduce the pest population below crop damaging densities. Other species showed a high pest reduction capacity and their potential for practical application can now be tested under commercial crop production conditions.

The South America Tomato Leafminer, Tuta absoluta (Lepidoptera: Gelechiidae), Spreads Its Wings in Eastern Africa: Distribution and Socioeconomic Impacts.

Following the arrival of Tuta absoluta Meyrick in the eastern African subregion in 2012, several studies have shown numerous ecological aspects of its invasion. We investigated the impact of T. absoluta on people's livelihoods across four counties of Kenya. Here, 200 farmers in the country were interviewed in person using semistructured questionnaires. In addition to livelihood surveys, T. absoluta distribution was mapped between 2016 and 2018 to determine its current distribution across four countries (Kenya, Sudan, Tanzania, and Uganda) in the subregion. Albeit a recent invader, T. absoluta is abundant and distributed throughout the subregion and is viewed as the worst invasive alien species of agriculturally sustainable livelihoods by tomato farmers. The arrival of T. absoluta in the subregion has resulted in livelihood losses and increased both the cost of tomato production and frequency of pesticide application. We recommend the implementation of biological control along, with other control measures in an integrated approach, against T. absoluta in the subregion, where its impact on sustainable livelihoods is serious and long-term control strategies are required to curb its detrimental effects.