Hans. E. Hummel(1,2,3), R. L. Lampman(2,3), R. J. Novak(2,3), R. L Metcalf(3)
1 Biological and Biotechnical Plant Protection, Justus Liebig University, Ludwigstrasse 21 b, D-35390 Giessen - Germany
2 IllinoisNaturalHistorySurvey,1910 GriffithDr.,Chainpaign,Il. 61820 - USA
3 Department of Entomology, University of Illinois, Urbana, Il. 61801 - USA
D. v. virgifera (Coleoptera: Chrysomelidae) is a leaf beetle aggressively invading South European maize fields. If unchecked, it will cause future damage and treatment costs in Europe in the same order of magnitude to those in the US where they recently amount to 1 billion dollars annually.
From an original focus next to Belgrade airport, D. v. virgifera spread over the last decade into neighboring Romania, Hungary, Croatia, and Italy, and is advancing rapidly.
Diabrotica pest problems have been dealt with mainly at the larval stage for several decades all over the US cornbelt. Environmental pollution, insecticide resistance, premature degradation of pesticides by soil organisms and, recently, failure of crop rotation in the system maize/soybeans have been some of the major obstacles encountered with the conventional toxicological approach.
In the absence of a satisfactory solution, new approaches are mandatory and are vigorously being pursued. Most promising seem to be the non-polluting biological and biotechnical strategies which do not have as target the metabolic pathways of the insects, but rather work by behavioral disruption, e.g. interference with adult mate searching behavior, or feeding and oviposition. Volatile semiochemicals such as sex pheromones and kairomones or non-volatile natural products such as cucurbitacins and neem ingredients are benign components of the agroecosystems anyway and meet the requirements of biodegradability and ecological compatibility. Their recognition and use as ecotechnical agents may open new avenues of behavioral control via communication and orientation disruption (Hummel, 1983, 1986, 1989b).
Diabrotica spp., in spite of numerous contributions by leading labs, have unfortunately still a poorly investigated chemical ecology. Sex pheromones have been described for D. barberi, D. v. virgifera (A), and D. undecimpunctata howardi (B). Recently, the kairomones MPE (4-methoxy-phenylethanol) (C) and MCA (4-methoxy-einnamaldehyde) (D) for D. barberi and D. v. virgifera, respectively, have been added to the list of known semiochemicals (Metcalf & Metcalf, 1992) with great expectations not only for their use as improved trapping and monitoring tools, but also for trap and kill, communication disruption (Hummel & Metcalf, 1996), and possibly as modifiers of oviposition behavior.
New is the discovery that D. v. virgifera, both male and female, are being attracted and disrupted by the kairomone MCA. Moreover, MCA causes a shift in sex ratio of trapped beetles, biased towards a temporary, reversible, relative decrease of females in comparison to untreated controls (Hummel et al., 1998a,b; 1999).
New is also the approach of broadcasting the semiochemicals as granular point sources from ground or air based systems (Hummel et al., 1998b, 1999).
The behavioral communication and orientation towards baited traps has been disrupted both in D. barberi and D. v. virgifera by permeation at rates between 40 and 100 g / ha to a degree of 40 to 100 % (Hummel & Metcalf, 1996). The degree of disruption varies with the size of the treated area, rate of volatilization, and additional factors still under investigation. Other, less volatile semiochemicals also may be used as disruptants:
Cucurbitacins, bitter natural products contained in original members of the Cucurbita family, are potent attractants and arrestants of Diabrotica spp. They can impede the ability of D. u. howardi and, to a lesser extent, of D. v. virgifera to orient towards traps baited with sex pheromones of the respective Diabrotica species (Hummel & Andersen, 1982).
Well known, but in this context less well investigated, are the effects of neem ingredients, e.g. azadirachtin and congeners, to disrupt Diabrotica communication. Our reports (Hummel, 1989b; Hummel 1986, 1989a) seem to be unnoticed, although the effects are quite striking and should be investigated further. Under the influence of neem oil, D. v. virgifera behave quite sluggishly. Their ability and inclination to take flight in neem oil treated fields are reduced. Also their sex pheromone communication, measured as orientation ability towards sex pheromone baited traps in the field, is considerably reduced (Hummel, 1989b). Improving the practicality of the disruption approach will be the subject of a EU sponsored project to be conducted in Southern Europe during the next 3 years.