Biology and Pest Management of the
Sunflower Beetle in North Dakota (continued)
E-824 (Revised,) March 2000
Pest Management
In the spring, overwintering sunflower beetle adults emerge, locate, feed, mate, lay eggs, and damage emerging sunflower plants. To effectively manage sunflower beetles, producers should use an Integrated Pest Management (IPM) Program. This type of approach can maximize yields and profits and minimize losses. Sunflowers should be monitored on a regular basis to determine the level of infestation and damage. To minimize inputs, to conserve the natural enemies of the sunflower beetle, and to reduce the negative impacts of pesticides on the environment, insecticides are only recommended when beetle populations have reached the "economic threshold level."
Cultural Control
Cultural control manages insect pests by altering farming practices, is compatible with conserving natural enemies, and is environmentally friendly. Two different cultural strategies that have been studied for sunflower beetle management are:
Planting Date
For the sunflower beetle, adult and larval populations decrease as planting date is delayed. Defoliation is also lowest in the latest planting date. As a result, delayed planting was effective in preventing yield reductions caused by sunflower beetle feeding. A further benefit was that no negative impacts were observed on the parasitism rate of the tachinid fly, Myiopharus macellus (Rheinhard), which attacked the sunflower beetle larvae equally in all of the different planting dates. Delayed planting also has been shown to reduce losses (seed weight or oil content) caused by the sunflower stem weevil (Cylindrocopturus adspersus (LeConte)) and the banded sunflower moth (Cochylis hospes Walsingham). But, damage from the red sunflower seed weevil (Smicronyx fulvus LeConte) tends to be greater in later-planted fields. Thus, sunflower planting decisions need to be based on the historical pest problems for a particular area. In addition, growers should consider that sunflower fields planted late (early June) usually have lower yields than fields planted early (mid to late May).
Tillage/Cultivation
Research has demonstrated that spring or fall cultivation does not reduce the overwintering populations of sunflower beetle adults or influence the pattern of emergence from the soil during the spring and summer. However, another sunflower pest, the red sunflower seed weevil, is negatively affected by tillage, which reduces emergence of adult seed weevils.
Plant Resistance
As yet, sunflower hybrids with resistance to the sunflower beetle have not been developed. Studies with about 20 species of native sunflowers have shown the genetic basis for resistance is present in some of these species. The resistance mechanisms exhibited in these native species include both antibiosis, in which larval mortality is higher when feeding on the plants, or antixenosis (non-preference), which is evident in reduced feeding by adults and larvae. In some cases, adult longevity was reduced and females laid no eggs. Although not killed outright, development time of beetles when feeding on some wild species was lengthened and their weights were reduced. The reduced vigor of these low-weight beetles makes them more vulnerable to attack by their natural enemies in the field.
Biological Control
The sunflower beetle has a number of natural enemies that either directly consume the various stages of the beetle or parasitize these stages with the progeny of the parasitoid destroying the beetle egg, larva or adult. Since these natural enemies are present in sunflower fields, it is important to protect them from unnecessary applications of pesticides which will kill them along with the sunflower beetles. By applying insecticides only when the pest density reaches the economic threshold, the predators and parasitoids are protected and allowed to serve as natural control agents for the sunflower beetle.
Predators
Many different insect predators feed on the different life stages of the sunflower beetle. Sunflower beetle eggs are eaten by the melyrid beetle, Collops vittatus Say, the thirteen spotted lady beetle, Hippodamia tredecimpunctata tibialis (Say), and the convergent lady beetle, H. convergens Guerin-Meneville. Larvae of the common green lacewing, Chrysoperla carnea Stephens, consume both eggs and larvae. The spined soldier bug, Podius maculiventris (Say), has been seen feeding on adults and larvae in North Dakota. The twospotted stink bug, Perillus bioculatus (Fabricius) (Figure 6), has been observed feeding on sunflower beetle larvae in Manitoba, Texas, and North Dakota. In North Dakota, a more rare, related stink bug species (Perillus circumcinctus Stal) is also present in sunflower fields and feeds on beetle larvae. The carabid beetle, Lebia atriventris Say, was reported to feed on sunflower beetle larvae in Manitoba and Texas (Figure 7). It appears to be a common inhabitant of sunflower fields in North Dakota and Minnesota. Laboratory studies have shown it to be a voracious feeder on sunflower beetle larvae. In Manitoba, damsel bugs, Nabis sp., were the fourth most common predator in sunflower fields and were suspected of feeding on sunflower beetle larvae. These predators are also common in North Dakota sunflower fields.
Figure 6a. Predator of sunflower
beetle: adult twospotted stink bug,
Perillus bioculatus (Fabricius).
(Click here for larger, 25KB photo)
Figure 6b. Nymphs of twospotted stink
bug, Perillus bioculatus (Fabricius)
feeding on a sunflower beetle larva.
(Click here for larger, 37KB photo)
Figure 7. Predator of sunflower beetle:
adult carabid beetle, Lebia atriventris Say.
(Click here for larger, 39KB photo)
Although they are a serious pest of sunflowers in many areas of the state at certain times
of the year, redwinged blackbirds also feed on sunflower beetle adults. A variety of
spider species are common inhabitants of cultivated fields and undoubtedly consume adults
and larvae of the sunflower beetle.
Parasitoids
Parasitoids attack sunflower beetle eggs, larvae, and adults. Eggs are parasitized by the pteromalid wasp, Erixestus winnemana Crawford, in North Dakota, Minnesota, and Manitoba. Reported parasitism rates are much lower in the U.S. (1 percent) than in Canada (17 percent). Larvae are parasitized by two species of parasitic flies of the family Tachinidae, Myiopharus macellus and M. doryphorae (Riley) in Manitoba, North Dakota and Minnesota (Figure 8). Myiopharus doryphorae has only been recovered from Canada and is extremely rare, constituting less than 1 percent of parasitoids reared from sunflower beetle larvae. The life history of M. macellus is well synchronized with the life cycle of its host, and the rate of parasitization is high in some fields in both Canada and the U.S. (up to 70 and 100 percent, respectively). The fly develops in the beetle larva, kills the larva when it moves into the soil to pupate, and emerges from the soil. Since the sunflower beetle overwinters as an adult, the fly must either overwinter in an alternate host or move into the northern plains from southern areas each year. Adult sunflower beetles are parasitized by the tachinid, Myiopharus sp. Approximately 0.2 to 17 percent of adults in Manitoba are attacked, but studies have shown that less than 2 percent are para-sitized in North Dakota and Minnesota.
Figure 8. Parasitoid of sunflower beetle: adult tachinid fly, Myiopharus macellus (Rheinhard). (Click here for larger, 30KB photo)
Chemical Control
Monitoring
Field scouting is necessary to determine whether or not a field needs to be treated. When monitoring a field, count the number of adults and/or larvae on 20 plants at five randomly selected sampling sites throughout the field for a total of 100 plants. Use a "X" pattern and select sampling sites at least 75 to 100 feet from the field margins. Determine the average number of adults and/or larvae per plant. Estimate the percent defoliation (Figure 9) during field scouting.
Figure 9. Various levels of percent defoliation (5-50 percent) caused by sunflower beetle feeding.
5%
10%
15%
20%
25%
30% 35% 40% 45% 50%
Economic Thresholds
Seedling:
1 to 2 adult(s) per seedling
Later plant growth stages
(vegetative to reproductive):1 to 2 adult(s) per plant
10-15 larvae per plant
OR
25 to 30 percent foliar defoliation
on the top 10-15 leaves or the
"active growing part"
In the seedling stage, one-two adults per seedling is the recommended economic threshold.
As sunflower plants develop, they can tolerate more feeding damage. When populations reach
10 to 15 larvae per plant, approximately 25 percent defoliation on the upper eight-12
leaves occurs. When adult populations average two adults per plant, enough larvae are
often produced to cause yield losses of 20 percent. Management is normally advised if
defoliation reaches the 25 to 30 percent level in late vegetative and early bud stages and
it appears (based on larval size of less than 1/4 inch or 6 mm) that more defoliation will
occur on the actively growing part of sunflower plant. However, if defoliation is 25
percent and the majority of larvae are about 1/3 inch (8 mm) long, they will have reached
maturity and stopped feeding. Then management is not be warranted.
Insecticide Recommendations
Application of an insecticide is recommended only when beetle populations have reached an economic threshold level in a field. Insecticides are effective in preventing economic loss when applied to actively feeding adults and/or larvae. Insecticides registered for sunflower beetle management in North Dakota as of 2000 are listed in the table below. Please check with the current Field Crop Insect Management Guide for updated insecticide registrations. It is of utmost importance that insecticide users READ, UNDERSTAND, and FOLLOW ALL LABEL DIRECTIONS.
Insecticide Recommendations
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Dosage in Product
Insecticide lb ai/acre per acre Restrictions on use
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Asana XL* 0.015 - 0.03 2.9 - 5.8 Do not apply within 28 days of
esfenvalerate lb/acre fl oz harvest. A reduced rate has been
issued as a state 2 (ee) label.
RUP These lower rates are for control
of SF beetle larvae ONLY. The
reduced rate application has a
range of 1.45 - 5.8 fl oz.
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Baythroid* 0.025 - 0.044 1.6 - 2.8 Do not apply within 30 days
cyfluthrin lb/acre fl oz of harvest.
RUP
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carbaryl 1.5 - 2 rate Do not apply within 60 days of
(Sevin) lb/acre varies by harvest. Do not allow livestock
formulation to graze on treated forage.
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Furadan 4F* 0.125 - 0.5 0.25 - 1 pt Do not re-enter treated fields
carbofuran lb/acre within 14 days of application
RUP without wearing proper protective
clothing. Do not harvest crop within
28 days of last application.
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Lorsban 4E 0.5 - 0.75 1 - 1.5 pts Do not apply within 42 days of
chlorpyrifos lb/acre harvest. Do not allow livestock to
graze in treated areas.
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Scout X-TRA* 0.005 - 0.01 0.71 - 1.42 Do not apply within 21 days of
tralomethrin lb/acre fl oz harvest.
RUP
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Warrior T* 0.015 - 0.025 1.92 - 3.2 Do not apply within 45 days of
lambda lb/acre fl oz harvest. A reduced rate has been
cyhalothrin issued as a state 2 (ee) label. The
RUP reduced rate application has a range
of 1.28 - 2.56 fl oz.
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* RUP - Restricted use pesticide
E-824 (Revised,) March 2000
