The effect of relative humidity on the development of the FAW egg parasitoid Telenomus remus Nixon
By: Alice dos Reis Fortes; Aloisio Coelho Jr.; José Roberto Postali Parra
A possible natural enemy for biological control of the Fall Armyworm, Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera: Noctuidae), is the wasp Telenomus remus Nixon, 1937 (Hymenoptera: Platygastridae), an egg parasite used in control programs in some parts of Latin America. The efficiency of T. remus is linked to its ability to parasitize all the layers of an S. frugiperda egg mass. This gives it an advantage over parasitoids of the genus Trichogramma spp. (Hymenoptera: Trichogrammatidae), which are widely used in biological control programs but parasitize only the eggs in the surface layer of the mass.
Among the abiotic factors that can directly influence the parasitism and biology of a parasitoid, temperature and relative humidity (RH) have been relatively well studied. The biological characteristics of T. remus reared on its natural host S. frugiperda are apparently not affected by RH. At RHs of 40%, 60% and 80%, the percentages of parasitism are 82.67%, 80.81% and 72.72% and the viabilities are 90.18%, 89.33% and 86.18%, respectively; in contrast, a sex ratio with more females is obtained at 40% RH (Pomari-Fernandes et al., 2015).
Telenomus remus is currently being reared on its natural host S. frugiperda. However, maintaining a population of this armyworm in the laboratory for mass production is impracticable, since larval S. frugiperda cannibalize each other and must be reared individually. In search of a suitable factitious host for large-scale T. remus rearing, some investigators have evaluated Corcyra cephalonica Stainton, 1865 (Lepidoptera: Pyralidae). Tests of T. remus reared on C. cephalonica at RHs of 40%, 60% and 80% showed that the parasitoid performs best at a RH of 80%, with a parasitism capacity of 28.40%, viability of 86.18% and sex ratio of 0.85 (Pomari-Fernandes et al., 2015).
Available data demonstrate that the RH does not affect biological parameters of T. remus over the egg-adult period, which is around 12.5 days. However, the RH may strongly affect the biological parameters of immature wasps, especially when reared on a factitious host. Temperature and RH are the abiotic factors that most influence the spatial distribution of insects; therefore, more precise studies are needed to evaluate the effect of RH on the biology of T. remus.
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