General herbivore outbreak following an El Niño-related drought in a lowland Panamanian forest

Abstract

A severe outbreak of Lepidoptera followed the 1997–98 El Niño Southern Oscillation event, during which the climate in central Panama was unusually dry. The outbreak involved the larvae of at least 12 species of Lepidoptera and occurred at a seasonally dry, deciduous forest site, where extensive background data were available regarding climate, tree species and non-outbreak herbivory levels. Most Lepidoptera were associated with only one or two larval host plant species belonging to the same family, and the majority were monophagous during this study. During the outbreak, caterpillar densities for the major outbreak species averaged 1.6 larvae per young leaf and 0.18 larvae per leaf for leaves of all ages. For canopy trees and lianas, the mean level of leaf damage was 13.8%, ranging from 1–100%. Seven out of 20 tree species sustained most of the damage, with 21–37% of the leaf area consumed. Relative to non-outbreak years, damage levels increased by more than 250% during the outbreak. Single-species outbreaks were observed in other areas with a similar drought, but wetter forests in central Panama did not experience outbreaks during this period. Historically, fewer outbreaks have been reported from tropical forests than from temperate forests, however, similar El Niño-related outbreaks have occurred recently in several other locations throughout the tropics.

Caterpillar abundance and parasitism in a seasonally dry versus wet tropical forest of Panama

“…Our results conflict with those of a previous study conducted at PNM in 1998 which showed that wasps were relatively scarce until the end of the wet season, while flies dominated the early part of the wet season (Van Bael et al 2004). The extended dry season of 1998 due to the El Nino Southern Oscillation resulted in a massive caterpillar outbreak with large trees being almost completely defoliated (Van Bael et al 2004). Therefore, results from these two studies may be explained by differences in collections of external feeders and shelter builders or annual variability in dryseason length and its impact on decoupling caterpillar and parasitoid populations.…”

Long-term Entomological Research on Canopy Arthropods in a Tropical Rainforest in Puerto Rico

“…Dominant vegetation includes tabonuco, Dacryodes excelsa Vahl (Burseraceae), which represents 35% of the forest canopy below 600 m elevation (Brown et al 1983 Tropical forests often are thought to be relatively stable. However, many tropical forests, including the LEF, are subject to frequent hurricane and drought disturbances, which alter the structure and composition of forest communities (Van Bael et al 2004, Scatena et al 2012). Prior to 1989, Puerto Rico had not experienced a major hurricane (≥ Category 3, >178 kph wind speed) for 33 years (Betsy in 1956), and a closed canopy with little understory characterized the forest.…”

“…Such long records aid greatly in identifying environmental factors responsible for population change (Morris 1964). Outbreaks are frequently triggered by drought or other host-stressing events (Mattson and Haack 1987;Van Bael et al 2004;Stige et al 2007;Schowalter 2012Schowalter , 2016. On the other hand, intolerant species may be eliminated by disturbances or require long periods for population recovery (Willig and Camilo 1991).…”

A Recent Outbreak of the Hawaiian Koa Moth,Scotorythra paludicola(Lepidoptera: Geometridae), and a Review of Outbreaks between 1892 and 2003

“…For example, in the wet tropics, fluctuations in rainfall can have drastic effects on insect dynamics (Kirkpatrick 1957, Harvey andMallya 1995). Tropical insect populations fluctuate annually (Wolda 1978), and outbreaks do occur, though they are relatively rarely reported (Fletcher 1967, Gray 1972, Piyakarnchana 1981, Harvey and Mallya 1995, Van Bael et al 2004). …”