Effects of rainfall on parasitism and survival of Telenomus remus, an egg parasitoid of fall armyworm

Abstract

Telenomus remus is an egg parasitoid of Spodoptera species, including the major agricultural pest Spodoptera frugiperda. Climatic factors are closely related to the development and population dynamics of such parasitoids. However, the effects of rainfall on the biological performance of this wasp have not be studied. Here, we modeled the effects of different intensities of rainfall (control: 0, light rain: 5.0, moderate rain: 10.2, and torrential rain: 42.8 mm/h; falling over a 30 min period) on the parasitism rate, developmental time, and survival of T. remus on eggs of S. frugiperda. We assessed the effect of rainfall exposure on both T. remus adults and on parasitized S. frugiperda eggs. Simulated rainfall resulted in a notable decline in the number of hosts parasitized by T. remus adults for up to 12 h following rainfall, but the parasitism rate returned to normal within one day after rain ceased. Torrential rain reduced immediate (within 24 h) survival of adults of T. remus females, but there was no subsequent effect on adult survival after rain ceased. When parasitized host eggs were exposed to rain events, some eggs were dislodged. Moderate or torrential intensity rainfall dislodged 12 and 44% of S. frugiperda eggs from maize leaves. For T. remus eggs exposed to rain that were not dislodged, the probability of reaching adulthood and successfully emerging was negatively correlated with rainfall intensity. However, for all levels of rainfall intensity, the survival of eggs that were not dislodged was greater than those that were dislodged. These findings suggest farmers should avoid releasing natural enemies when rainfall occurs or is forecast, and they should make supplemental releases after unanticipated rainfall occurs immediately after releases.