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

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.

supplementary material Text S15

S15 Supplementary text Differences in experimental conditions
The lifetable data presented as supplementary material files S 1-14 and the values for r m and k m given in Tables 2 and 3 resulted from experiments under similar temperature conditions (24-26 o C). The relative humidity conditions were not always similar and varied between 45 and 80%, but it is not expected that this variation is of great influence, though no scientific proof is available to support this assumption. However, development, predation and parasitism all take place on the plant-leaf surface and within enclosed experimental arenas with different levels of ventilation. It is supposed that under these conditions humidity on the leaf surface is higher than that of the ambient climate room environment. Also, photoperiods varied (range from 12-12 to 16-8 L:D) and light intensities were not similar. These differences may have influenced rates of predation and parasitism if the natural enemies are only active during the light period.
Nocturnal predation rates for the three Neotropical mirid predators (C. infumatus, E. varians and M. basicornis) were similar to values for predation rates obtained during the daylight period (Broekhuizen 2017). Therefore, it is supposed that the predation data for all six mirid species for which r m and k m values are presented in this paper are not influenced by different photoperiods during the experiments.
Nocturnal parasitism was not tested for any of the parasitoid species discussed in this paper. If parasitoids do not parasitize during the night, this may have a larger influence on daily rates of parasitism for proovigenic species than for synovigenic ones. Proovigenic parasitoids have all or a major part of their eggs matured when the females emerge and their daily number of eggs laid will be determined, among others, by the length of the day. The experiments with the proovigenic D. gelechiidivoris took place with a 12 h photoperiod, while those with T. pretiosum and T. bactrae had a 14 h period. As a result, the r m and k m values for the larval parasitoid D. gelechiidivoris might be slightly underestimated when compared with the two egg parasitoid species because the larval parasitoid had fewer hours available for parasitism and the total amount of eggs laid may, as a result, have been realized after more days than with a 14 h photoperiod. Synovigenic parasitoids usually need food during their adult life in order to be able to mature eggs and generally produce a limited number of eggs per day, depending on the rate of egg maturation. Thus, synovigenic parasitoids may still lay all their mature eggs at the shortest photoperiod to which they were exposed, i.e. in all but one case 14 hours, and it is supposed that their r m and k m values are not strongly influenced by the length of the photoperiod. Reference: Broekhuizen, T.M. Prey selection, predation during night and oviposition site selection by three Neotropical mirids. MSc thesis, Wageningen University, The Netherlands, 49 pp. (2017).

S16 Summary of data of intrinsic rate of population increase of Tuta absoluta
The published r m values given in the table below vary between 0.074 and 0.19, with most values in the range of 0.13-0.19. The differences in r m values may be the result of many causes, including different origin and rearing histories of T. absoluta populations, different tomato cultivars expressing varying degrees of host plant resistance, large differences in experimental procedures, and different ways of calculating the population parameters. The value provided for T. absoluta in Table 3 is one of the highest found. Most other r m were determined by the Birch approach and values will be slightly higher when calculated with the Lotka-Euler approach. As no raw data for lifetables of the pest were available in the papers summarized in the table below, the Lotka-Euler approach could not be applied. In the discussion section of the paper an r m of the pest in the range of 0.13-0.19 is used for comparison with the k m of the natural enemies. However, when speculating about control capabilities of natural enemies, determination of the r m of the pest on the tomato cultivars locally used is relevant.   Orius insidiosus ? _____________________________________________________________________________________________ +++ = very good predation by mirids, ++=good predation by mirids, +=predation found but still needs to be quantified, ?=not yet tested