Technology
Dyes show promise for control of fire ants Studies indicate that xanthene dyes inhibit acetylcholinesterase to cause death in fire ants, other insect pests
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Lethal photooxidation catalyzed by certain dyes may play a role in future control of fire ants and other insect pests. Although the exact mechanism of how light and dye sensitization acts is unclear, apparently it is inactivation of acetylcholinesterase in fire ants that causes their death, according to a re search group at Mississippi State Uni versity headed by biochemist James R. Heitz. The imported fire ant, Solenopsis richteri (Forel), believed to have arrived in the U.S. from South America in 1919, builds mounds that interfere with
Mississippi State's Lancelot Lewis (left) and Dr. James R. Heitz collect fire ant specimens from a mound 46
C&ENSept. 23, 1974
farm machinery operation in southern states from North Carolina on the north to central Texas on the west. It also attacks small forms of wildlife. Control efforts have relied largely on insecticides—especially a relatively persistent organochlorine material, Mirex, now under attack as an envi ronmental hazard. The xanthene dyes that Dr. Heitz and his associates use— rose bengal is an example of a com mon, effective one—have the advan tage of relatively rapid photodegradation and they appear to present minimal environmental problems. In tests, the dyes were added to su crose solutions, which were fed to test ants.. The physiological characteristics connected with death of the ants suggest that some aspect of nerve trans duction may be the site of the photoox idation reaction, Dr. Heitz told the Di vision of Pesticide Chemistry. Data ob tained so far by the Mississippi group show a strong correlation existing be tween effectiveness of the dye as an in hibitor of acetylcholinesterase and phosphorescence quantum yield. The scientists interpret this to mean that the excited triplet state of the dye in teracts with ground-state oxygen, playing a critical role in the photoox idation of the enzyme. Various conditions of dye dosage, type of light and its duration, and time required for mortality have been inves tigated. Generally, light comparable to daylight intensities gives faster kills of dye-fed ants than does laboratory fluo rescent lighting of 3800 microwatts per sq. cm. Dye concentrations of 4.9 X 10~ 3 M in a 1% sucrose solution fed the ants are effective, causing half the ants to die in less than four hours. Exposure times required for death aren't nearly as important as are concentrations of dye in the ants' tissues. Experimental comparisons of various kinds of dyes—rose bengal, phloxin B, rhodamine B, and erythrosin Β (in order of decreasing effectiveness)—in dicate that dyes with more high-molec ular-weight halogens connected to the xanthene ring system are most effec tive, Dr. Heitz says. Light isn't abso lutely necessary for the dyes to cause death of the ants. But since the time for mortality is in days rather than hours and since the enzyme appears to remain active in the absence of light, Dr. Heitz suggests that a different bio chemical mechanism seems to be in volved in the lethal dark reaction. Other scientists had found a similar photooxidation of trypsin caused death
Rose bengal
of the domestic housefly—work which, in fact, led Dr. Heitz's group to try the xanthene dyes on fire ants. Other work now under way at Dr. Heitz's laboratory has provided preliminary data that photooxidation might be effective against the tobacco budworm and the cotton boll weevil. Dr. Heitz hopes to try field tests of the xanthene dyes on fire ants this fall, if funding is obtained. The work so far has been carried out since January with funds from the Mississippi Agri cultural and Forestry Experiment Sta tion and the MSU Office of Graduate Research.
Lower cost promoters used to make TPA 168TH rfCS NhTIONhL meeTING High-purity terephthalic acid produced by oxidation of p-xylene requires large amounts of methyl ethyl ketone as a promoter for the reaction. Research at Mobil Chemical, Edison, N.J., indi cates, however, that other, less expen sive promoters can be used without sacrificing product purity. The compa ny's Dr. John D. Behun told a sympo sium on oxidation studies, held jointly by the Division of Industrial and Engi neering Chemistry and the Division of Petroleum Chemistry, that terephthal ic acid produced with η-butane as a
