To us insectometers, it is clear that insect decline in our Costa Rican tropics is real, so let's be kind to the survivors

Abstract

We have been field observers of tropical insects on four continents and, since 1978, intense observers of caterpillars, their parasites, and their associates in the 1,260 km² of dry, cloud, and rain forests of Área de Conservación Guanacaste (ACG) in northwestern Costa Rica. ACG's natural ecosystem restoration began with its national park designation in 1971. As human biomonitors, or "insectometers," we see that ACG's insect species richness and density have gradually declined since the late 1970s, and more intensely since about 2005. The overarching perturbation is climate change. It has caused increasing ambient temperatures for all ecosystems; more erratic seasonal cues; reduced, erratic, and asynchronous rainfall; heated air masses sliding up the volcanoes and burning off the cloud forest; and dwindling biodiversity in all ACG terrestrial ecosystems. What then is the next step as climate change descends on ACG's many small-scale successes in sustainable biodevelopment? Be kind to the survivors by stimulating and facilitating their owner societies to value them as legitimate members of a green sustainable nation. Encourage national bioliteracy, BioAlfa.

Keywords: BioAlfa; biodevelopment; climate change; conservation by rewilding; insect decline.

Fig. 1.

Área de Conservacion Guanacaste (ACG), northwestern Costa Rica, inside the white polygon covering ∼1,680 km² from 6 km out into the Pacific Ocean, across the dry forest lowlands, over the cloud forested Cordillera Guanacaste (∼1,400- to 2,000-m elevation), and down into the Caribbean rain forest lowlands (∼1,260 km² terrestrial). These are the three major tropical forested ecosystems. In ACG, they cover an area the size of New York City and its suburbs. We currently estimate that this terrestrial and freshwater area (approximate center at latitude 10.83764, longitude −85.61871, 300 m) contains at least a half million species of arthropods, based on our inventory and opportunistic sampling throughout ACG since 1978, and the ∼45,000 species collected by the first year (2014 to 2015) of intense sampling with Malaise traps. One of our standard Townes-type Malaise traps captured no fewer than 14,520 species of true insects during two consecutive years (14).

Fig. 2.

Clouds of the cloud forest in ACG (red mountaintops in Fig. 1), Volcán Orosí (Left) and Volcán Cacao (Right) as viewed from the Pacific side of Costa Rica. In the 1980s, the standard view was a solid mass of clouds generated by the east-to-west trade winds pushing moist Caribbean air up and over the cordillera (Bottom image). When this air condenses, it creates a foggy and dripping cloud forest on the mountaintops. By the mid-1990s, a common view was a mix of 1980s views and many days with a fractured and much smaller cloud layer (Middle image). This was accompanied by drying forest litter, obvious reduction in epiphyte loads, and frequent reductions in stream flow. Today, there are often days with no clouds at all (Top image), mixed with days of a heavy cloud layer as in the 1980s, but the bottom of that layer is now 100 to 500 m higher in elevation. Heavy fog no longer swirls in through open doors and windows of the Cacao Biological Station at 1,100 m and ants are now a conspicuous part of the fauna at the station, whereas they were essentially absent when ACG was established in the mid-1980s (37, 38) because the soil and litter were too cold and wet for them.

Fig. 3.

A normal 1980s assembly of moths at the Cliff Top light trap about 2 wk after the beginning of the rainy season, at the dark of the moon, 9 to 10 PM. The large black, gray, and white sphingid in the center, Manduca rustica, is a migrant from the Caribbean rain forest side of ACG, arriving with the rains, after a flight of perhaps 20 to 40 km. There are five local and univoltine Manduca dilucida on the sheet, easily recognized by their paired white shoulder patches. The elongate abundant dark moths on the right half of the sheet are local and largely univoltine Crinodes besckei and C. ritsemae (Notodontidae). All four of these species are now rare at this light trap station, as are now their caterpillars in the forest at any time of year.

Fig. 4.

The same light trap as Fig. 3, 23 y later, same time in the rainy season and moon cycle, with the mass of moths normally present at this time of year since the 1970s. The cinnamon brown endemic Schausiella santarosensis (Saturniidae) are abundant on the right side (the UV-rich blacklight side), and there are the usual omnipresent, yellow, as-yet-undescribed species of Eacles (Saturniidae) (as also visible in SI Appendix, Fig. S2).

Fig. 5.

The same light trap as viewed in Figs. 3 and 4, on 30 May 2019 at the same time in the moon cycle (dark) and 2 wk after the beginning of the rainy season. There are, as usual, two large yellow Eacles (as in SI Appendix, Fig. S2) on the ground in front of the white sheet. This dramatic change in moth density and species richness has now come to represent light trap catches in the ACG dry forest at the beginning of the rains (as repeated May 2020), and we have less extreme examples in the ACG cloud and rain forest as well, since about 2014 to 2015.