Colorado Potato Beetle Management, Radcliffe s IPM World Textbook
Colorado Potato Beetle Management
- 1 Colorado Potato Beetle Management
- 2 Introduction
- 3 Biology and Life Cycle
- 4 Management Options — Commercial Grower
- 5 Management Options — Home Gardeners and Certified Organic Growers
- 6 UK Plant Health Information Portal An online hub for plant health information, data and resources
- 7 Colorado beetle
The Colorado potato beetle, Leptinotarsa decemlineata (Say), is a major pest of potato, Solanum tuberosum L., in commercial production and home gardens in Minnesota. Larvae and adults both feed on foliage and if left untreated, complete defoliation of plants (Figure 1) is possible. The Colorado potato beetle was first recognized as a pest of potato in Colorado in 1859 after settlers introduced potatoes into the insect%;s native range of the eastern Rocky Mountains. The native host for this insect is a relative of potato, buffalo bur (Solanum rostratum). It took the beetle about 30 years to adapt to potato. But, once Colorado potato beetles had adapted to feeding on potato, the beetles migrated to the east using potatoes grown in farms and gardens throughout the Great Plains and Ohio River Valley. On average, the Colorado potato beetle expanded its range eastward approximately 85 miles per year, reaching the East Coast by 1874. The insect has since become established in Europe and spread eastward to the Urals and Turkey. Potato growers have struggled to control this insect since 1865 when the first broad-spectrum insecticide, Paris green (lead arsenate), was dusted onto potato leaves to protect the foliage from Colorado potato beetles.
Biology and Life Cycle
Detailed Life History. Adult Colorado potato beetles (Figure 2) are about half the size of your thumbnail, oval in shape, and are a yellow-orange color with 10 narrow black stripes on the forewings (elytra). The adult Colorado potato beetle overwinters in the soil either in the potato field itself or in field margins. In Minnesota, the beetle overwinters most successfully in windbreaks and other wooded areas surrounding potato fields. The following spring, adults begin to emerge (Figure 3) at about the same time potatoes emerge. Adults feed for a short while in the spring, then begin to mate and lay clusters of 10 – 30 yellow eggs on the underside of the leaf (Figure 4). Females typically lay 350 or more eggs during their lives that can last several weeks. The Colorado potato beetle has few natural enemies, and those that do feed on the eggs, larvae, pupae, or adults have little impact on the Colorado potato beetle populations.
Larval Development. Eggs hatch within 1-2 weeks, depending upon temperatures (Table 1). Larvae remain aggregated near the egg mass when young (Figure 5) but begin to move throughout the plant as that leaf is consumed (Figure 6). Larvae molt four times getting progressively larger each time. Over 75% of the defoliation caused by the immatures occurs during the last (4th) larval instar (Figure 7). Young larvae are brick red with a black head capsule while 3rd and 4th instar larvae are pink to salmon colored with a black head capsule. The sides of the larvae have two rows of dark spots. Larvae can complete development in as little as 8-10 days if the average temperatures are in the mid 80%;s while it will take over a month if temperatures average near 60 F. The fourth instar larvae eventually drop from the plant, and burrow into the soil to pupate.
Table 1. Colorado potato beetle development (days) in relation to average daily temperatures.
eggs to hatch
|Days to complete
|Days for summer
adults to appear
* No insects pupated at these temperatures. Adapted from Vegetable Insect Management, Meister Publishing.
Summer Adults. Summer adults (Figure 8) begin to emerge in 1-3 weeks following pupation. In southern and central Minnesota, there is generally a partial second generation. Which is to say, that some of the summer adults feed only briefly then migrate to the field margins, windbreaks and wood lots where they burrow into the ground to overwinter. Other summer adults will feed voraciously, mate, and lay eggs. The primary trigger that determines whether individual beetles mate or go into reproductive dormancy is daylength at the time of adult emergence. By mid summer, a potato field can have all stages of Colorado potato beetles, eggs, larvae and adults. You can tell if you have overwintering adults or summer adults by looking at the hind or membranous wings. The overwintered adults have a smoky-orange cast to their wings with distinctive orange veins. The hind wings of the summer adults are clear.
Management Options — Commercial Grower
The Colorado potato beetle is one of the few “super” pests in agriculture. This species has developed resistance to most insecticides. Care must be used when targeting Colorado potato beetles to select an effective insecticide. You should also recognize that once you have to increase the rate to get adequate control, resistance to that insecticide is likely present in the population. Commercial growers have a number of insecticides that perform well. Fortunately, many of the newer insecticides have a unique mode of action giving growers the opportunity to delay the onset of resistance by rotating chemical classes. If growers carefully select insecticides for Colorado potato beetle control, these products should remain effective for years to come. Repeated use of the same insecticide or other insecticides from the same chemical class will speed development of insecticide resistance. Slowing the onset or even preventing insecticide resistance is called resistance management and all growers should practice some form of resistance management.
For the home gardener and certified organic producer, the choice of effective chemicals is limited and none will give perfect control. Insecticide choices for commercial growers are given in Table 3 and products available for home gardeners and certified organic growers are given in Table 4. There are more insecticides available to commercial growers but nearly all of these insecticides are classified as restricted use materials so that to purchase them you must be a certified pesticide applicator. Also, many insecticides are sold only in large quantities making them generally impractical for the home gardener.
Resistance Management. There are several key components of any resistance management program. First and foremost is to not repeatedly use the same insecticide or other insecticides having a similar mode of action to control Colorado potato beetles on the same farm in successive years. In fact, growers should not use the same insecticide to control the overwintering generation and the summer adults and any larvae they produce (2nd generation) in a given growing season. Historically, it has taken from 4 to 10 generations of repeated exposure to the same or similar insecticide for resistance to occur in Colorado potato beetles. In Minnesota this can mean 3-5 years in southern and central Minnesota where there are 2 generations per year and 4-10 years in the Red River Valley where Colorado potato beetles have a single generation most years. A good “rule of thumb” is if an insecticide performed well for you against the overwintering adults and young larvae don%;t use it on the summer adults or again the following spring. Switch insecticides and if possible use an insecticide from a different chemical class that has a different mode of action (Table 3and Table 4).
Cultural Control. Crop rotation is an effective method of reducing your risk to Colorado potato beetles. The greater distance a potato field is located from a last year%;s potato field, the later in the season the field will become colonized with beetles, greatly reducing the potential for damage. Colorado potato beetles cannot fly unless temperatures reach 70 F. In early spring in Minnesota, daytime temperatures can be substantially below 70 F effectively making beetles walk from the overwintering site to locate a potato field.
Resistant Varieties. NewLeaf potato varieties are marketed under contract with NatureMark, a subsidiary of Monsanto (http://www.naturemark.com/). These genetically modified plants have incorporated a bacterial gene from Bacillus thuringiensis var. tenebrionis that produces a protein that is toxic only to beetles. There are a limited number of varieties that have been genetically engineered and are available for commercial use only (Table 2). Currently, NatureMark does not market the NewLeaf variety of potatoes to the home gardener and commercial growers must sign a Technology Agreement that stipulates that:
- NewLeaf seed may only be used for production of one crop,
- Potatoes must not be replanted or held over for seed use the following growing season,
- NewLeaf seed may not be resold without penalty,
- NewLeaf varieties may comprise no more than 80% of potato acres on an individual farm unit, for the purpose of resistance management.
Table 2. NewLeaf potato varieties produced by NatureMark Potatoes.
|Variety||Beetle Control||Plant disease control|
|NewLeaf 6 Russet Burbank||Yes||None|
|NewLeaf Plus 82 Russet Burbank||Yes||Yes, PLRV|
|NewLeaf Plus 129 Russet Burbank||Yes||Yes, PLRV|
|NewLeaf Plus 350 Russet Burbank||Yes||Yes, PLRV|
|NewLeaf Y 101 Russet Burbank||Yes||Yes, PVY|
|NewLeaf 6 Atlantic||Yes||None|
|NewLeaf 31 Atlantic||Yes||None|
|NewLeaf 36 Atlantic||Yes||None|
|NewLeaf 5 Superior||Yes||None|
|NewLeaf Y 46 Hi-Lite||Yes||Yes, PVY|
|NewLeaf Y 2 Shepody||Yes||Yes, PVY|
|NewLeaf Y 15 Shepody||Yes||Yes, PVY|
When using NewLeaf potato varieties beneficial insects are not harmed. This is an important feature because natural enemies can be relied upon to provide effective control of other potato pests such as aphids. NewLeaf potatoes produce the protein toxin in all green tissues and beetle mortality is essentially 100%. To slow down the development of resistance to this protein toxin, commercial growers must agree to plant at least 20% of their potato acreage to standard varieties and use conventional insecticides for Colorado potato beetle control on this 20%.
Chemical Control. Commercial production of potatoes is nearly impossible without using insecticides to control Colorado potato beetles. Commercial growers have the option of using systemic insecticides applied to the soil or seed at planting or apply insecticides to foliage after crop emergence. Using a systemic insecticide at planting is justified if there is a history of beetle treatment each growing season. If beetle pressure is not always severe, foliar applied insecticides can be the better choice because that permits assessment of beetle pressure before deciding on treatment. Also, invasion of a field may occur from one side of the field and treating field edges or “hot spots” is an option available to those who use a foliar applied insecticide.
All insecticides are most effective on very young larvae. Eggs and pupae are not susceptible to chemical control and adults can be difficult to control. Targeting application toward young larvae helps prevent damaging populations and allows resistant adult beetles to mate with susceptible beetles keeping selection pressure for insecticides resistance low. If sprays are targeted against overwintering adults, the only survivors will be resistant individuals. When resistant individuals mate, their offspring are resistant thus fixing the resistance gene in the population. Once resistance has become fixed in a population, reversion to susceptibility occurs only after many generations of non-exposure and may never revert to pre-exposure levels.
Foliar materials are best applied between 15 and 30% egg hatch for best control.
A second foliar application may be necessary if egg laying continues over an extended period. You can predict 15-30% egg hatch by flagging 100 egg masses in the field and checking them daily. Alternatively, insecticide application could begin when egg hatch has occurred on 5-10% of the plants. Waiting to spray until beetles are in the late 3rd and early 4th instar is not a wise strategy. Large larvae are difficult to control and since the 4th instar larvae are responsible as much as 75% of the feeding damage, earlier treatment is usually necessary to prevent economic damage. Determining if a beetle population is large enough to treat is not easy. Potatoes can tolerate up to 30% defoliation prior to flowering but only 10% defoliation at the onset of tuber initiation. Failure to control the first generation larvae may translate into large numbers of summer adults that emerge and feed during the critical tuber initiation and tuber bulking stage.
It is particularly important in potatoes that insecticides used to control Colorado potato beetle don%;t flare aphids. Multiple applications of foliar insecticides to control summer adults and larvae of Colorado potato beetle are commonly associated with aphid outbreaks. Insecticide applications disrupt the predators and parasitoids that would otherwise hold aphid populations in check. Additionally, when fungicides are used repeatedly to prevent foliar diseases such as late blight in combination with insecticides, aphid populations can build to such high levels that foliage will die. The only insecticides that provides reliable control of green peach aphid are imidacloprid (Admire and Provado) and methamidophos (Monitor). By keeping insecticide applications at a minimum, green peach aphids generally will not reach pest status. Repeated use of insecticides for either Colorado potato beetle or potato leafhopper control can flare green peach aphid populations.
Table 3. Insecticides* available to control Colorado potato beetles. Most are restricted use pesticides.
|Trade name||Common name||Site / Mode of Action||Application Method|
|Admire||imidacloprid||Central Nervous System / neurotoxin||In-furrow at planting or seed treatment|
|Provado||imidacloprid||Central Nervous System / neurotoxin||Foliar|
|Thimet||phorate||Central Nervous System / acetylcholinesterase inhibitor||In-furrow at planting or side dress at hilling|
|Di-Syston 15G||disulfoton||Central Nervous System / acetylcholinesterase inhibitor||In-furrow at planting or side dress at hilling|
|Di-Syston 8EC||disulfoton||Central Nervous System / acetylcholinesterase inhibitor||Foliar|
|Imidan||phosmet||Central Nervous System / acetylcholinesterase inhibitor||Foliar|
|Guthion||azinphosmethyl||Central Nervous System / acetylcholinesterase inhibitor||Foliar|
|Furadan||carbofuran||Central Nervous System / acetylcholinesterase inhibitor||Foliar|
|Sevin||carbaryl||Central Nervous System / acetylcholinesterase inhibitor||Foliar|
|Vydate||oxamyl||Central Nervous System / acetylcholinesterase inhibitor||In-furrow at planting or foliar|
|Baythroid||Cyfluthrin||Central Nervous System / axonic poison, sodium channel disrupter||Foliar|
|Ambush||Permethrin||Central Nervous System / axonic poison, sodium channel disrupter||Foliar|
|Asana||Cypermethrin||Central Nervous System / axonic poison, sodium channel disrupter||Foliar|
|Thiodan||endosulfan||Central Nervous System / sodium and potassium balance in neurons||Foliar|
|Raven||Bacillus thuringiensis var. kurstaki||Stomach poison||Foliar|
|M-Trak||Bacillus thuringiensis var. tenebrionis||Stomach poison||Foliar|
|Colorado Potato Beetle Beater (Bonide)||Bacillus thuringiensis var. san diego||Stomach poison||Foliar|
|Novodor||Bacillus thuringiensis var. tenebrionis||Stomach poison||Foliar|
|AgriMek||Abamectin||Neurotoxin, GABA inhibitor||Foliar|
|Spintor||Spinosad||Gamma receptor (neurotoxin)||Foliar|
|Kryocide||Cryolite||Inhibits enzymes with iron, calcium or magnesium centers||Foliar|
|Azatin XL Plus||Azadirachtin||Interference with molting, repellent||Foliar|
|Rotenone/Pyrethrin Spray (Bonide)||Rotenone||Respiratory enzyme inhibitors of fish and insects, not mammals||Foliar|
* Note: For specific rate recommendations for a given product, or label changes, refer to the annually revised “Midwest Vegetable Production Guide for Commercial Growers” (BU-7094-S).
Management Options — Home Gardeners and Certified Organic Growers
For homeowners, the general use insecticides that are available locally are largely ineffective because of widespread insecticide resistance of the Colorado potato beetle. An example of this is the insecticide Sevinâ (carbaryl). Insecticides derived from botanical sources, e.g., rotenone and neem, may be available from catalogs or larger nurseries and greenhouse supply centers. The botanical insecticides can give adequate control of Colorado potato beetle provided they are applied frequently and young larvae are targeted. In general, botanical insecticides break down rapidly and need to be reapplied frequently and generally give poor control of large larvae and adults. There are a few insecticides that are derived from bacterial toxins. One available to the home gardener is a product from Bonide, Colorado potato beetle beater.
Cultural control practices such as crop rotation is largely ineffective because of space consideration in home gardens. Planting an early maturing variety will also allow you to escape much of the damage caused by adults emerging in mid-summer. Check you seed catalogs for varieties that mature in less than 80 days. Yield on early maturing varieties are not as large, and often these varieties do not store as well as the popular Russet Burbank potato. Mechanical destruction of the insects is always an option and depending upon the size of the garden can be effective. Remember to look on the underside of leaves for egg masses and remove or crush the egg masses when found.
If you choose to use an insecticide to control Colorado potato beetles, the same resistance management strategies apply to home gardeners as they do to commercial growers.
All insecticides are most effective on very young larvae. Eggs and pupae are not susceptible to chemical control and adults can be difficult to control. Targeting application toward young larvae helps prevent damaging populations and allows resistant adult beetles to mate with susceptible beetles keeping selection pressure for insecticides resistance low. Foliar materials are best applied between 15 and 30% egg hatch for best control. Because eggs may be laid over a several week period, repeated application is necessary for good control. Waiting to spray until beetles are in the late 3rd and early 4th instar is not a wise strategy. Large larvae are difficult to control and since the 4th instar larvae are responsible as much as 75% of the feeding damage, earlier treatment is usually necessary to prevent severe crop loss. Potatoes can tolerate up to 30% defoliation prior to flowering but only 10% defoliation after flowering.
Altogether, control of Colorado potato beetle in the home garden can be a challenge, but not an impossible task. Armed with knowledge of the insect%;s biology, damage potential and available control options should allow you to successfully produce a crop.
Table 4. Insecticides* available to control Colorado potato beetles for the home gardener.
|Trade name||Common name||Site / Mode of Action||Application Method|
|Colorado Potato Beetle Beater (Bonide)||Bacillus thuringiensis var. san diego||Stomach poison||Foliar|
|Azatin XL Plus||Azadirachtin||Interference with molting, repellent||Foliar|
|Rotenone/Pyrethrin Spray (Bonide)||Rotenone||Respiratory enzyme inhibitors of fish and insects, not mammals||Foliar|
|Sevin||carbaryl||Central Nervous System / acetylcholinesterase inhibitor||Foliar – note largely ineffective due to resistance|
* Note: For specific rate recommendations read and follow the directions on the product label. You may also refer to the annually revised “Midwest Vegetable Production Guide for Commercial Growers” (BU-7094-S).
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Colorado potato beetle (Leptinotarsa decemlineata [Say]) is the most important insect defoliator of potatoes. It also causes significant damage to tomato and eggplant. One beetle consumes approximately 40 cm 2 of potato leaves at a larval stage, and up to additional 9.65 cm 2 of foliage per day as an adult (Ferro et al., 1985). In addition to impressive feeding rates, Colorado potato beetle is also characterized by high fecundity, with one female laying 300-800 eggs (Harcourt, 1971). Furthermore, the beetle has a remarkable ability to develop resistance to virtually every chemical that has ever been used against it.
Since Colorado potato beetle shifted from its original wild hosts in southwestern North America, it has spread throughout the rest of the continent and has invaded Europe and Asia. Currently its distribution covers about 8 million km2 in North America (Hsiao, 1985) and about 6 million km 2 in Europe and Asia (Jolivet, 1991). It has appeared recently in western China and Iran. Potentially the Colorado potato beetle can occupy much larger areas in China and Asia Minor, spread to Korea, Japan, Russian Siberia, certain areas of the Indian subcontinent, parts of North Africa, and the temperate Southern Hemisphere (Vlasova, 1978; Worner, 1988; Jolivet, 1991).
The Colorado potato beetle has a complicated and diverse life history. The beetles overwinter in the soil as adults, with the majority aggregating in woody areas adjacent to fields where they have spent the previous summer (Weber and Ferro, 1993). The emergence of post-diapause beetles is more or less synchronized with potatoes. If fields are not rotated, they are colonized by overwintered adults that walk to the field from their overwintering sites or emerge from the soil within the field (Voss and Ferro, 1990). If fields are rotated, the beetles are able to fly up to several kilometers to find a new host habitat (Ferro et al., 1991; 1999). Once they have colonized the field, the overwintered beetles first feed and then oviposit within 5-6 days depending on temperature (Ferro et al., 1985; Ferro et al., 1991).
Eggs are usually laid on the underside of potato leaves. Upon hatching, larvae may move over short distances within potato canopy and start feeding within 24 hours of eclosion. Development from the time of oviposition to adult eclosion for pupae takes between 14-56 days (de Wilde, 1948; Walgenback and Wyman, 1984; Logan et al., 1985; Ferro et al., 1985). The optimal temperatures range between 25-32ºC and appear to differ among populations of different geographic origins. The larvae are capable of behavioral thermoregulation via moving within plant canopies (May, 1981; Lactin and Holliday, 1994), thus optimizing their body temperature compared to the ambient temperature. Pupation takes place in the soil near the plants where the larval development has been completed.
Diapause is facultative, and the beetles can have between one and three overlapping generations per year. It takes a few days for the newly emerged adults to develop their reproductive system and flight muscles (Alyokhin and Ferro, 1999). After development has been completed, the beetles mate and start laying eggs. The reproduction continues until diapause is induced by the short-day photoperiod, then the beetles migrate to overwintering sites (mainly by flying), and enter the soil to diapause. Those beetles that emerge under short-day photoperiod do not develop their reproductive system and flight muscles that season. They feed actively for several weeks and then either walk to the overwintering sites or burrow into the soil directly in the field (Voss, 1989).
Colorado potato beetle’s diverse and flexible life history is well-suited to unstable agricultural environments, and makes it a complex and challenging pest to control. Flight migrations closely connected with diapause, feeding and reproduction allow the Colorado potato beetle to employ «bet-hedging» reproductive strategies, distributing its offspring in both space (within and between fields) and time (within and between years). Such strategies minimize the risk of catastrophic losses of offspring, otherwise quite possible in unstable agricultural ecosystems (Solbreck, 1978; Voss and Ferro, 1990).
Chemical Control and Insecticide Resistance
Since 1864, hundreds of compounds were tested against the Colorado potato beetle (Gauthier et al. 1981), and insecticides still remain the foundation of the Colorado potato beetle control on commercial potato farms. Currently, more than 30 active ingredients are registered for use against this pest in the United States. Insecticide efficiency and availability, however, vary from area to area. The same is true about pesticide regulations. Therefore, people considering using chemicals to control beetles should contact a local extension agent or other qualified professional.
An important thing to keep in mind is that Colorado potato beetle has a legendary ability to develop resistance to a wide range of pesticides used for its control. High predisposition to resistance development seems to be an inherent characteristic of this species. It is probably caused, in large part, by the coevolution of the beetle and its host plants in the family Solanaceae, which have high concentrations of toxins, namely glycoalkaloids (Ferro, 1993). The first instance of Colorado potato beetle resistance to synthetic organic pesticides was noted for DDT in 1952 (Quinton, 1955). Resistance to dieldrin was reported in 1958, followed by resistance to other chlorinated hydrocarbons (Hofmaster et al., 1967). In subsequent years the beetle has developed resistance to numerous organophosphates and carbamates (Forgash, 1985). Presently it is resistant to a wide range of insecticides, including the arsenicals, organochlorines, carbamates, organophosphates, and pyrethroids. Resistance crisis was temporarily abated with the introduction of highly effective neonicotinoid insecticides. However, the first cases of beetle resistance to neonicotinoids have been already observed in several field populations (Alyokhin et al., 2006; 2007; Mota-Sanchez et al., 2006).
The major problem area is the Northeastern United States (Forgash, 1985); however, resistance has also been detected in Michigan (Ioannidis et al., 1991), Canada (Stewart et al., 1997), and Europe (Forgash, 1985; Boiteau, 1988). In some cases, a new insecticide failed after one year (e.g., endrin) or even during the first year of use (e.g., oxamyl) (Forgash, 1985). Resistance mechanisms are highly diverse even within a relatively narrow geographical area (Ioannidis et al., 1991). Furthermore, the beetles show cross-resistance to organophosphates and carbamates, and multiple resistance to organophosphates, carbamates, and pyrethroids (Ioannidis et al., 1991). In addition to the resistance to synthetic insecticides, the beetle has a capability to develop resistance to the Bacillus thuringiensis subsp. tenebrionis delta-endotoxin (Whalon et al., 1993; Rahardja and Whalon, 1995).
Colorado potato beetle populations can be reduced through the use of relatively common cultural practices such as crop rotation, manipulation of planting time and crop varieties, use of mulches, cover and trap crops (Hough-Goldstein et al., 1993). Crop rotation for the Colorado potato beetle control had been first recommended as early as 1872 (Bethune, 1872), and since then proved to be a good control strategy not only for the beetle, but also for a number of potato pathogenes and weeds (Casagrande, 1987). At the rotated field, peak density of the beetle egg masses could be less than 10% of that of the non-rotated field (Lashomb and Ng, 1984). Wright (1984) reported that when potatoes were planted following a non-host grain crop (rye or wheat), early season Colorado potato beetle adult densities were reduced by 95.8%.
Late and early planting is aimed to suppress the second generation larval populations. Because summer-generation adults emerge later in the season on the late-planted crop, the short-day photoperiod stimulates reproductive diapause, largely eliminating the second-generation larval impact on the crop. Early planting also eliminates the second generation larvae, in this case because the crop is already being removed at the time of their emergence (Weber and Ferro, 1995).
Trap crops may be used to attract beetles away from the main crop. It has been shown to intercept both overwintered beetles colonizing a field in the spring (Weber and Ferro, 1995), as well as the beetles moving away from senescing potatoes late in the season (Hoy et al., 1996).
Another promising technique of Colorado potato beetle cultural control is mulch applications. Larval populations of the beetle were significantly reduced in straw- mulched plots of potato (Stoner, 1993) and eggplant (Stoner, 1997). A peak of the small (1st — 2nd instar) larval populations was observed 1 — 2 weeks later on the mulched potato fields than on the unmulched ones (Stoner, 1993). Furthermore, the mulch may increase the time required by the beetles to find potatoes (Ng and Lashomb, 1983), decrease the likelihood of flying beetles locating the potato plants (East, 1993), increase the proportion of beetles leaving the area by flight (Weber et al., 1994), and increase predation on eggs and larvae (Brust, 1994). Overall, a six — ten cm layer of wheat straw produced 2.5-5 fold decrease in potato defoliation (Zehnder and Hough-Goldstein, 1990; Brust, 1994).
In addition to cultural control, a number of physical control methods can be used to suppress Colorado potato beetle populations. One possible method involves digging plastic-lined trenches along a field border in order to intercept post-diapause Colorado potato beetles colonizing the crop in the spring. In a one-month period, during which the majority of the beetles emerge from the soil, 1 m of such a trench can capture as many as 1,000 beetles (Ferro, unpublished data). Up to 95% of captured beetles are normally retained in the ditch (Misener et al., 1993).
Another method is to manipulate beetle diapause habitat in an attempt to enhance its overwintering mortality. In the experiment of Milner et al. (1992), wheat straw mulch was applied to the overwintering sites in the fall, and then removed together with the layer of snow covering it in January. This procedure rapidly depressed soil temperatures, and led to a significantly lower beetle survival (approximately 7% at disturbed habitats vs. approximately 26% at the undisturbed habitats).
Still other methods of physical control include propane flamers (Pelletier et al., 1995; Khelifi et al., 2007) and tractor-mounted vacuum collectors (Boiteau et al., 1992; Lacasse et al., 1998). Combining these two techniques increases their overall efficiency (Khelifi et al. 2007), making control level comparable to that of some insecticide treatments (Laguë et al., 1999).
High fecundity usually allows Colorado potato beetle populations to withstand natural enemy pressure. Still, in the absence of insecticides natural enemies can sometimes reach densities capable of reducing Colorado potato beetle numbers below economically damaging levels (Ferro, 1985).
Beauveria bassiana (Hyphomycetes) is a pathogenic fungus that infects a wide range of insect species, including the Colorado potato beetle. It is probably the most widely used natural enemy of the Colorado potato beetle, with readily available commercial formulations that can be applied using a regular pesticide sprayer. Applications of B. bassiana have been shown to reduce beetle populations by up to 75% (Cantwell et al.,1986). However, control is usually less effective compared to chemical insecticides (Campbell et al., 1985; Hajek et al., 1987).
A number of predatory and parasitic arthropods attack the Colorado potato beetle (Hough-Goldstein et al., 1993). The lady beetle Coleomegilla maculata consumes eggs and small larvae (Groden et al., 1990; Hazzard et al., 1991), killing up to 37.8% of eggs for the first Colorado potato beetle generation and up to 58.1% of eggs for the second generation (Hazzard et al., 1991). Predaceous stink bugs Perillus bioculatus and Podisus maculiventris attack beetle larvae. Inundative releases of these predators suppressed beetle density by 62% (Biever and Chauvin, 1992), reduced defoliation by 86% (Hough-Goldstein and McPherson, 1996), and increased potato yields by 65% (Biever and Chauvin, 1992) over the untreated control. Adult ground beetles Lebia grandis feed on the Colorado potato beetle eggs and larvae, while larvae of the same species parasitize the Colorado potato beetle pupae (Weber et al., 2006). The parasitic wasp Edovum puttleri was found to parasitize 71-91% of Colorado potato beetle egg masses on eggplant, killing 67-79% of the eggs per mass (Lashomb et al., 1987). The level of parasitism is somewhat lower in potatoes, rarely exceeding 50% (Ruberson et al., 1991; Van Driesche et al., 1991). Performance of Edovum puttleri in the field can be further improved by the supplementary use of an artificial carbohydrate source (Idoine and Ferro, 1990).
Several species of generalist predators also occasionally feed on the Colorado potato beetle. Fourteen species of carabid beetles, three species of Coccinellidae, and a spider, Xysticus kochi, are known to feed on the Colorado potato beetle in the former Soviet Union (Sorokin, 1976). Eight species of Lebia and five other ground beetle species attack this pest in Mexico (Logan, 1990). Another ground beetle, Pterostichus chalcites, has been observed feeding on the Colorado potato beetle in Delaware (Heimpel and Hough- Goldstein, 1992). The daddy-long-legs Phalangium opilio preys on the beetle’s eggs and small larvae (Drummond et al., 1990).
Although Colorado potato beetles are fully capable of completely wiping out potato crops, at low-to-moderate beetle densities potato plants are fairly tolerant to the inflicted defoliation. They can tolerate 30-40% defoliation during early growth stages, 10-60% defoliation during middle growth stages, and up to 100% defoliation late in the season without noticeable yield reduction (Hare, 1980; Cranshaw and Radcliffe, 1980; Ferro et al., 1983; Shields and Wyman, 1984; Zehnder and Evanylo, 1988). In the same time, currently there are no truly resistant cultivars. Conventional potato breeding is complicated by tetraploidy in S. tuberosum (Grafius and Douches 2008). Genetically modified potatoes expressing Bacillus thuringiensis delta-endotoxin that is toxic to the Colorado potato beetle were introduced in the U.S. in 1995, but then discontinued after only five years of use, in large part because of consumer concerns about genetically engineered foods.
Cultural practices may enhance plant ability to resist the Colorado potato beetle. Lower beetle densities have been recorded in plots receiving manure soil amendments in combination with reduced amounts of synthetic fertilizers compared to plots receiving full rates of synthetic fertilizers, but no manure (Alyokhin et al., 2005). No reduction in plant vigor in the absence of synthetic fertilizers was observed in that study. Subsequent field-cage and laboratory experiments (Alyokhin and Atlihan, 2005) confirmed that potato plants grown in manure-amended soil were indeed inferior Colorado potato beetle hosts compared to plants grown in synthetically fertilized soil.
Integrated Pest Management
The secret of Colorado potato beetle’s success as a pest is its diverse and flexible life history coupled with a remarkable adaptability. Therefore, to be successful in our control efforts we also need to be diverse and flexible in our approaches, as well as adaptable to ever-changing circumstances. Mindless reliance on a single tactic is doomed to fail, no matter how fundamentally sound this tactic is. The only sustainable way to manage this insect is integration of multiple control techniques based on a scientifically sound understanding of its biology.
Control in Home Gardens
In addition to creating problems in commercial production, the Colorado potato beetle is also a concern for home gardeners. When garden is limited to a few potato, tomato, or eggplant plants, hand-picking overwintered adults and egg masses early in the season is the simplest management approach. Most damage is done by larvae, so removing their parents and unhatched eggs should provide fairly good protection of the plants later in the season. It is no more time-consuming than other gardening practices, does not require expensive purchased inputs, and environmentally friendly. It can also be a relaxing and somewhat therapeutic experience – after all, from the biological point of view we have evolved to be hunters and gatherers, not computer programmers or hedge fund managers. The picking should be done for several weeks because overwintered beetles exit diapause and colonize host plants over approximately one-month time window.
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