Agriculture Reference
In-Depth Information
pest management (IPM) to guide insecticide sprays and on the roughly 1% of farm-
ers who rely entirely on natural biocontrol. Depending on whether the soybean
price was the 1996-2007 median or the higher post-2007 level, the reduced value
of biocontrol services to soybeans due to the 19% increase in corn acreage was esti-
mated to be $18-25 ha
−1
for IPM farmers and $110-199 ha
−1
for natural biocontrol
farmers (Landis et al. 2008).
Another KBS LTER approach to measuring the economic value of the soy-
bean aphid natural enemy complex used a bioeconomic model that predicted
densities of the pest and its predators (as opposed to habitat features in the land-
scape). Zhang and Swinton (2009) developed a dynamic optimal control model
for soybean aphid IPM that incorporates the economic value of natural enemy
survival when making profit-maximizing decisions on insecticide applications
to the aphid. They found that natural enemies are particularly valuable for
suppressing low populations of soybean aphid, preventing them from multiply-
ing to the point of causing significant crop damage. A single, typical natural
enemy (comparable to the multicolored Asian lady beetle,
Harmonia axyridis
)
per soybean plant is worth $32.60 ha
−1
when 5 to 30 aphids are present per
plant during its early flowering stage (Fig. 3.2). However, above 30 aphids,
the value of a single natural enemy would fall to just $4.20 ha
−1
, because at
higher aphid populations, a single natural enemy could not control the infesta-
tion so insecticides would be needed to maximize profit (in spite of the col-
lateral or nontarget damage to natural enemy populations) (Zhang and Swinton
2012). Based on evidence that soybean aphid density averaged 21 per plant in
40
30
20
10
0
0
25
50
75
100
125
150
Soybean Aphids per Plant
Figure 3.2
. Value of one natural enemy per soybean plant (as compared to none) as a func-
tion of the abundance of soybean aphids. The aphids are assumed to be in reproductive stage
R1, the natural enemy is assumed to have a daily predation rate of 35 aphids, and the initial
soybean yield potential is assumed to be 2.69 Mg ha
-1
. Redrawn from Zhang and Swinton
(2012) with permission from Elsevier.
