Population Biology

The size, structure, energetics, composition, and mobility of insect populations in various life zones, macrohabitats, and mi-crohabitats are highly significant, and a very large body of literature on both theoretical and applied insect demography exists (Young 1982). Such investigations always require quantitative analysis of population parameters, and particular sampling techniques are needed in each specialty area (Southwood 1980, Wolda 1984).

Most works deal with specific insects (Ehrlich and Gilbert 1973), often of economically important types, limited taxa (Torres 1984), or guilds (unrelated species with similar niches) (Heithaus 1979) within particular environments. Some of this research may include comparisons between different habitat types. Investigations of whole communities are very few owing to their complexity and their multifold interactions with the environment.

The lower layers of tropical forests (lowland, midlatitude moist to rain forests) have attracted the most attention from insect population biologists in Latin America. Sampling is direct; specimens can be observed directly or captured fairly easily with nets, the "sweeping" technique often being used for soft foliage, herbs, or grasses (Allan et al. 1973,Janzen 1973). An intensive thirteen-month survey of Amazonian forest was undertaken in 1977-78 in the Ducke Forest Preserve near Manaus (Penny and Arias 1982), for which passive Malaise traps caught most of the samples.

Long-term studies are rare (Wolda 1983). Over a period of several years, Elton (1973) sampled the forest "field layer" (15 cm to 1.8 m above the ground) in a variety of localities and with different methods and concluded that insect life generally exists in low numbers and that the sizes of most are small but that the species richness is very high. The most common forms found were ants, spiders, and orthopteroids. The very diverse nocturnal fauna of flying insects is composed of much larger insects.

Using sweep net samples to study diversity and distribution, various authors (e.g., Janzen 1973) have discovered profound differences along elevational transects, for example, in Costa Rica and the Venezuelan Andes (Janzen et al. 1976). Latitudinal effects (Janzen and Pond 1975) as well as seasonal effects (Janzen and Schoener 1968, Tanaka and Tanaka 1982) have also been included.

Light trapping has revealed some popu-lational traits of Neotropical insects (Rick-lefs 1975; Wolda 1978a, 19786). In lowland forest, the seasonality of flight activity of nocturnal forms is pronounced. Generally, numbers are depressed in the mid-dry period and maximally expanded in the early weeks of wetness in both mainland (Wolda 1980) and island (Tanaka and Tanaka 1982) areas. The suppressive effect of moonlight on the activity of night-flying insects is also often noted (Wolda and Flowers 1985).

The insects of the forest canopy, although now accessible by special techniques, resist quantitative study because of the difficulties remaining in taking sizable samples and covering a significant area of habitat. Some advances have been made in the study of canopy bee biology by climbing entomologists (Perry 1983). Traps (Malaise, "photocollectors") have also been raised to upper levels for remote assessment. In this way, three responses by arboreal insects in Amazon inundation forests have been detected during the flood season: temporary immigration, survival in place, and dying out (Adis 1977).

A fruitful approach for obtaining statistically adequate data from the canopy has come from the insecticide fogging technique. Rapid-acting pyrethroids are blown into the trees. (These mildly toxic chemicals rapidly degrade in the environment

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