Combination of generalist predators, Nesidiocoris tenuis and Macrolophus pygmaeus, with a companion plant, Sesamum indicum: What benefit for biological control of Tuta absoluta?

Tuta absoluta is one of the most damaging pests of tomato crops worldwide. Damage due to larvae may cause up to 100% loss of tomato production. Use of natural enemies to control the pest, notably predatory mirids such as Nesidiocoris tenuis and Macrolophus pygmaeus, is increasingly being promoted. However, considering the potential damage caused to tomatoes by these omnivorous predators in the absence of T. absoluta, an alternative solution could be required to reduce tomato damage and improve the predators’ performance. The use of companion plants can be an innovative solution to cope with these issues. The present study aimed to determine the influence of companion plants and alternative preys on the predators’ performance in controlling T. absoluta and protecting tomato plants. We evaluated the effect of predators (alone or combined) and a companion plant (sesame (Sesamum indicum)) on T. absoluta egg predation and crop damage caused by N. tenuis. The influence of an alternative prey (Ephestia kuehniella eggs) on the spatial distribution of predators was also evaluated by caging them in the prey presence or absence, either on tomato or sesame plants or on both. We found that the presence of sesame did not reduce the efficacy of N. tenuis or M. pygmaeus in consuming T. absoluta eggs; hatched egg proportion decreased when N. tenuis, M. pygmaeus, or both predators were present. More specifically, this proportion was more strongly reduced when both predators were combined. Sesame presence also reduced necrotic rings caused by N. tenuis on tomato plants. Nesidiocoris tenuis preferred sesame over tomato plants (except when food was provided only on the tomato plant) and the upper part of the plants, whereas M. pygmaeus preferred tomato to sesame plants (except when food was provided only on the sesame plant) and had no preference for a plant part. Combination of predators N. tenuis and M. pygmaeus allows for better coverage of cultivated plants in terms of occupation of different plant parts and better regulation of T. absoluta populations. Sesamum indicum is a potential companion plant that can be used to significantly reduce N. tenuis damage to tomatoes.

Distribution, abundance and natural enemies of the invasive tomato leafminer, Tuta absoluta (Meyrick) in Kenya

Tuta absoluta (Meyrick) has become a serious menace to sustainable production of tomato in Kenya. A survey was conducted between April 2015 and June 2016 to determine its distribution, abundance, infestation, and damage levels on tomato, and associated natural enemies. Trap counts of T. absoluta moths were recorded in all surveyed 29 counties, which indicated its nationwide distribution irrespective of altitude. Tuta absoluta was present in both open fields and greenhouses. The highest moth/trap/day was 115.38 ± 15.90. Highest leaf infestation was 92.22% and the highest number of mines and larvae per leaf were 3.71 ± 0.28 and 2.16 ± 0.45, respectively. Trap captures in terms of moth/trap/day were linearly and positively related to leaf infestations in open fields (R2 = 0.81) and greenhouses (R2 = 0.61). Highest fruits’ infestation and damage were 60.00 and 59.61%, respectively, while the highest number of mines per fruit was 7.50 ± 0.50. Nesidiocoris tenuis (Reuter) and Macrolophus pygmaeus (Rambur) were identified as predators of T. absoluta larvae. Nine species of larval parasitoids were recovered from infested foliage, with a combined parasitism of 7.26 ± 0.65%. Hockeria species was the most dominant (31.25%) and accounted for 12.88 ± 1.47% parasitism. Two species of larval parasitoids, Hockeria and Necremnus were obtained from sentinel plants with an average parasitism of 1.13 ± 0.25. The overall abundance and parasitism rates of recovered natural enemies were low to effectively control the field populations of T. absoluta. These findings form the basis of researching and developing effective and sustainable management strategies for the pest.

A risk-based detection survey for the predatory mirid Macrolophus pygmaeus in New Zealand

Macrolophus pygmaeus, a predatory mirid used to manage greenhouse whitefly, was illegally imported into New Zealand, and for a time was reared and sold to commercial tomato growers. We designed and implemented a risk-based detection survey to determine whether M. pygmaeus was still present in New Zealand a decade later. The survey was designed to have an 80% chance of detecting a single low density (0.05 per lineal metre of host plants) population within 1 km of known points of introduction. The survey was implemented between 8 and 15 March 2018. Local habitat constraints meant that the planned sampling had to be modified but this was accounted for in the subsequent analysis. No M. pygmaeus were found in the samples, but 93 specimens from seven other mirid taxa were detected, validating the sample methods. The survey gives 60% confidence that M. pygmaeus was not present at a mean density of 0.05 per lineal metre of habitat. It gives 80% confidence that a population at 0.1 m−1 was not present and 90% confidence that no population exists at >0.18 m−1. Though there are no published data on typical field population densities of M. pygmaeus, for related species the survey would have had high confidence in detecting any medium to high density population present. Therefore, it is likely that M. pygmaeus is no longer present in New Zealand, but if extant within the sampled areas then we have high certainty that it was at low densities compared to other predaceous mirids.