Re: Fisherman's grow blog
History
The beetle was discovered in 1824 by
Thomas Say from specimens collected in the
Rocky Mountains on buffalo-bur,
Solanum rostratum. The origin of the beetle is somewhat unclear, but it seems that
Colorado and
Mexico are a part of its native distribution in southwestern North America.[SUP]
[2][/SUP] In about 1840, the species adopted the cultivated potato into its host range and it rapidly became a most destructive pest of potato crops. The large scale use of insecticides in agricultural crops effectively controlled the pest until it became resistant to
DDT in the 1950s. Other pesticides have since been used but the insect has, over time, developed resistance to them all.[SUP]
[3][/SUP]
Life cycle
Colorado potato beetle larvae
Colorado potato beetle females are very prolific; they can lay as many as 800 eggs. The eggs are yellow to orange, and are about 1.5 mm long. They are usually deposited in batches of about 30 on the underside of host leaves. Development of all life stages depends on temperature. After 4–15 days, the eggs hatch into reddish-brown
larvae with humped backs and two rows of dark brown spots on either side. They feed on the leaves. Larvae progress through four distinct growth stages (instars). First instars are about 1.5 mm long; the fourth is about 8 millimetres (0.31 in) long. The larvae in the accompanying picture are third instars. The first through third instars each last about 2–3 days; the fourth, 4–7 days. Upon reaching full size, each fourth instar spends an additional several days as a non-feeding prepupa, which can be recognized by its inactivity and lighter coloration. The prepupae drop to the soil and burrow to a depth of several inches, then pupate. Depending on temperature, light-regime and host quality, the adults may emerge in a few weeks to continue the life cycle, or enter diapause and delay emergence until spring. They then return to their host plant to mate and feed. In some locations, three or more generations may occur each growing season.
As a crop pest
Colorado beetles are a serious pest of potatoes. They may also cause significant damage to tomatoes and eggplants. Both adults and larvae feed on foliage and may skeletonize the crop.
Insecticides are currently the main method of beetle control on commercial farms. However, many chemicals are often unsuccessful when used against this pest because of the beetle's ability to rapidly develop insecticide
resistance. The Colorado potato beetle has developed resistance to all major insecticide classes, although not every population is resistant to every chemical.[SUP]
[4][/SUP] In the
United Kingdom, where the Colorado beetle is a rare visitor on imported farm produce, it is a notifiable pest: any found must be reported to
DEFRA.
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. A ground beetle,
Lebia grandis is a predator of the eggs and larvae and its larvae are
parasitoids of the Colorado beetle's pupae.
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.
[h=4]Resistance Management[/h] Insecticides in the same chemical class usually have the same mode of action, the same method of killing the insect. Resistance develops more rapidly to an insecticide when that insecticide is used repeatedly as the only control measure. Repeated use of one class kills susceptible beetles, leaving those that are resistant. Overuse of one insecticide may favor the development of resistance to other insecticides in the same chemical class. Consequently, to delay or prevent resistance
it is important to avoid repeated usage of one particular insecticide by rotating the insecticides used.
NOTE: Not sure that BT is good for tobacco plant????????
Bacillius thuringiensis var tenebrionis (Bt) is effective against small larvae (less than 1/4 inch) and should be applied at egg hatch or when larvae are first seen. A premature treatment may lose much of its effectiveness before the eggs hatch. Larger larvae are more difficult to control with Bt. Azatin, an extract of the neem seed, prevents the larvae from developing normally.
