Agriculture Reference
In-Depth Information
Within this broader context, KBS LTER scientists have sought a deeper understand-
ing of the interactions of beneficial insects and crop pests in agricultural landscapes.
Determining Which Insects and Processes to Quantify
The KBS LTER Main Cropping System Experiment (MCSE) design was estab-
lished in 1989 (Robertson and Hamilton 2015, Chapter 1 in this volume) and
includes annual systems made up of corn (
Zea mays
L.)—soybean (
Glycine max
L.)—winter wheat (
Triticum aestivum
[L.]) rotations, alfalfa (
Medicago sativa
L.),
hybrid poplars (
Populus
sp.), and unmanaged successional ecosystems (Table 8.1).
Due to the long-term nature of the research, large 1-ha plots were established
with five permanently located monitoring sites within each. From an entomologi-
cal perspective, this sampling design presented both advantages and constraints.
Fixed sampling points provide the opportunity to follow spatial patterns over
time, but limit other types of investigations such as those involving dispersal and
predator-prey interactions. From the outset, a nontrivial question has been which
insects and ecological processes could best be studied within this framework.
A direct focus on insect herbivores was initially considered but ultimately set
aside, primarily because each crop can support multiple species of insect pests and
differences in pest life cycles and behaviors would require different, labor-intensive
sampling strategies. In addition, many insect sampling approaches require destruc-
tive methods that would be at odds with other study objectives and themselves
represent a disturbance to the ecosystems. Instead, we focused on insect predators
and parasitoids that engage in biological regulation of insect herbivores, and in par-
ticular on predatory ladybird beetles (Coleoptera: Coccinellidae). Since 1989 coc-
cinellids have been monitored in all MCSE systems at the main site and in selected
portions of the surrounding landscape.
Logistical requirements suggested adoption of a simple sampling method that
would minimally disturb the plant community but would capture the dynamics of
coccinellid predators and foster understanding of their ecological function, both in
time and space. A previous investigation of apple maggot (
Rhagoletis pomonella
Walsh) dispersal at KBS had successfully used transects of yellow sticky traps to
determine flight paths of adult flies dispersing to an isolated orchard adjacent to
the LTER main site (Ryan 1990). These sticky traps also captured many species of
dispersing Coccinellidae. Maredia et al. (1992a) determined the optimal trap color
to attract coccinellids and other key predators to be yellow, which was most attrac-
tive to
Coccinella septempunctata
(L.), the most abundant coccinellid, and equally
as attractive as other colors to
Hippodamia parenthesis
(Say) and
Chrysoperla
carnea
(Stephens) (Neuroptera: Chrysopidae). As a result, yellow sticky traps
(PHEROCON AM, Great Lakes IPM, Vestaburg, Michigan) have been deployed
since 1988. A pole supports the traps 1 m above the soil surface (Maredia et al.
1992b) at each permanent sampling location. Traps are deployed for a minimum of
8 weeks each year from May to September in each replicate plot of the MCSE sys-
tems, for a total of 255 sample sites. Each is visited weekly to record the abundance
of 17 species of Coccinellidae.
