Bagrada hilaris (Burmeister) 223
3.6.1.3 Action Thresholds
Little information is available on action thresholds used for making control decisions for Bagrada hilaris
on brassica crops. Nyabuga (2008) recommended an action threshold of three bugs per plant when initiat-
ing control of B. hilaris on kale. A damage threshold used for mustard crops of one bug/m^2 on early growth
stage plants and three bugs/m^2 on larger plants (Daiber 1991) also has been recommended for B. hilaris
control on caper crops (Infantino et al. 2007). Although a scientifically-validated action threshold has not
yet been established for B. hilaris on head-forming brassica crops in Arizona, a nominal threshold has
been established that recommends treating plants when numbers of adults or damaged seedlings exceed
one per six row feet of seedlings or transplants (Palumbo 2014). Maintaining B. hilaris densities below
this level can reduce stand losses and unacceptable plant damage (Reed et al. 2013b). Based on recent
work by Palumbo and Carrière (2015), the nominal threshold has been modified and now triggers insec-
ticide treatments when the number of head-forming brassica plants with fresh lesions exceeds 5%. The
threshold should be used for making management decisions until plants reach the six-leaf node stage, after
which plants are much less susceptible to crop losses (J. C. Palumbo, unpublished data).
3.6.1.4 Chemical Control
The predominant approach to Bagrada hilaris management in cole crops worldwide has been chemi-
cal control. B. hilaris adults can destroy seedling plants rapidly, and the lack of effective cultural and
biological control alternatives have forced growers to rely on quick-acting, contact insecticides to protect
their crops. Preventing adults from feeding on plant terminals and small cotyledons on commercial
brassica crops in Arizona and California is critical to establishing a marketable crop (Palumbo and
Natwick 2010, Reed et al. 2013b). Consequently, management of B. hilaris in these cropping systems has
consisted of intensive insecticide usage to protect seedling crops during crop establishment (Palumbo
2015b). Insecticide usage has almost doubled on cole crops since the arrival of B. hilaris to the desert
Southwest, and growers have indicated that over 90% of the broccoli crops produced from 2010 to 2014
received an average of four insecticide sprays per season to control B. hilaris (Palumbo 2015b).
Historically, growers in the Old World have relied on organochlorine, cyclodiene, organophosphate,
and carbamate insecticides to control Bagrada hilaris (Sarop et al. 1972, Bok et al. 2006, Hill 2008).
The majority of these older, highly toxic compounds that have been effective against B. hilaris either
are outdated or banned from use in the United States (Sarop et al. 1972, Gami et al. 2004, Ahuja et al.
2008, Nyabuga 2008, Singh et al. 2011b). However, among organophosphate and carbamate compounds
currently registered for use in the United States, only chlorpyrifos and methomyl have demonstrated
significant contact toxicity against B. hilaris adults in laboratory bioassays and field trials (Palumbo et
al. 2013b, Palumbo and Huang 2014a, Palumbo et al. 2015).
Presently, in many parts of the world, including North America, pyrethroids commonly are used for
control of Bagrada hilaris because of their fast knockdown efficacy (Infantino et al. 2007, Nyabuga 2008,
Obopile et al. 2008, Palumbo et al. 2015). Because of the quick-acting contact activity of pyrethroids,
growers in Arizona reported that pyrethroids are the primary insecticide used to control of B. hilaris
adults on seedling crops (Palumbo 2015b). Local laboratory bioassays and greenhouse trials have demon-
strated that pyrethroids such as bifenthrin and lambda cyhalothrin cause rapid contact mortality against
B. hilaris adults (Palumbo et al. 2015) and, in field efficacy trials, protect plants from damage for 5–7 days
following application (Palumbo 2012; Palumbo et al. 2013b, d, e; Palumbo and Huang 2014a).
Among the newer classes of insecticide chemistry, neonicotinoids such as imidacloprid and acetamiprid
applied as foliar sprays have been shown to control Bagrada hilaris (Singh et al. 2011b). Similarly, dinote-
furan applied to broccoli foliage is significantly more toxic to B. hilaris adults and provides significantly
better plant protection against B. hilaris adults than acetamiprid, thiamethoxam, imidacloprid and clo-
thianidin (Palumbo 2012; Palumbo et al. 2013b, c, d; Palumbo et al. 2015). Dinotefuran also has exhibited
antifeeding properties against B. hilaris adults (Palumbo et al. 2013d, Palumbo et al. 2015). The soil
systemic toxicity of neonicotinoids to B. hilaris adults in laboratory bioassays has shown that dinotefuron,
imidacloprid, and thiamethoxam are toxic to adults via ingestion (Palumbo et al. 2015), but their applica-
tion as at-planting soil treatments in field trials did not prevent B. hilaris from injuring seedling broccoli