A new biological phenomenon: The solitary population wave, and its role in the biological control of pests, weeds in particular

Abstract

A biological phenomenon consisting in the propagation of an ordered solitary wave has been observed in insects introduced into southern USSR. It is assumed that the same process also occurred during the establishment of beneficial organisms released for the biological control of weeds in Australia and North America (cf. Clark & Clark, 1952) for instance.In recent years, attempts were made to substantiate mathematically the phenomenon of solitary waves in natural populations (Ivanov, 1984), but this approach has remained purely theoretical. Over the last 20 years, "solitonics" was developed in the physics of non-linear processes, and solitary waves (solitons and autowaves) that move without changing shape were studied in physical, chemical, and biological media.During the establishment of Zygogramma suturalis Forster, a chrysomelid introduced from Canada for the biological control of ragweed (Ambrosia artemesiifolia L.), a spherical wave 1.5 km long and 10 m wide comprising some 10 million beetles was observed to move across a field of esparcet (Onobrychis viciifolia Scopoli) in USSR.The wave kept its shape and a velocity of about 3 m/day. This process calIed solitary population wave (SPW) was described by a mathematical model by Kovalev & Veehernin (1986). According to this model, the SPW holds an intermediate position between autowaves and solitons. The SPW has a high efficiency, the weed being totally destroyed in a short period. This movement was similar to the propagation of a steppe fire (autowave of burning). An insect SPW was initiated in an area where insects reached the critical density of 5 000 individuals/m front. The SPW differs from aggregations that occur during outbreaks and has only been observed in phytophagous species this far.SPW are probably common in nature and have been found in introduced arthropods and fungi. Optimal conditions for their formation are met during the establishment phase of an organism in a new ecological niche and SPW may be of great importance in terms of biological pest control. The study of SPW requires a special census technique based on mobile and stationary transects across the wave front. The transects were (l) Under this heading ENTOMOPHAGA publishes short contributions on those aspects of IPM and biological pest control that are of increasing importance but have not yet been seriously considered.

The ragweed leaf beetle Zygogramma suturalis F. (Coleoptera: Chrysomelidae) in Russia: current distribution, abundance and implication for biological control of common ragweed, Ambrosia artemisiifolia L.

“…As for the data obtained by other authors, the comparison is hampered by the fact that, very often, not average values but upper limits were published. Maximal Z. suturalis population density recorded in Stavropol' and Krasnodar territories at the end of the 1990s was six and 50-70 adults per square metre, respectively (Polovinkina and Yaroshenko, 1999;Os'kin, 2002), which is similar to our data obtained in 1988-1989(Reznik et al, 1994 but much higher than the results of the present. One of the recent papers (Esipenko and Belikova, 2004) also pointed out a significant decrease in the Z. suturalis population density.…”

“…In 1983, ragweed at the experimental release site was eliminated, and the ragweed leaf beetle began to spread over surrounding fields (Kovalev et al, 1983). Thus, the initial phase of this introduction was a population explosion with more than a 30-fold yearly increase in number, up to 100,000,000 adults/km 2 in fields and up to 5000 adults/m 2 in aggregations (Kovalev, 1988). In some cases, a 'solitary population wave', i.e.…”

“…In some cases, a 'solitary population wave', i.e. a moving zone of ultra-high population density, was observed (Kovalev, 1988). Following these waves, common ragweed was exterminated locally very quickly, which allows one to expect highly efficient biological control of the weed (Kovalev, 1988;Goeden and Andres, 1999).…”

“…a moving zone of ultra-high population density, was observed (Kovalev, 1988). Following these waves, common ragweed was exterminated locally very quickly, which allows one to expect highly efficient biological control of the weed (Kovalev, 1988;Goeden and Andres, 1999). From 1984From to 1986, a number of further releases were made in the south of European Russia and Ukraine, but the population wave was not subsequently observed, possibly because the insects were released in regularly exploited agricultural landscapes but not in special protected sites (Reznik et al, 1994).…”

Diapause behaviour of Zygogramma bicolorata (Coleoptera: Chrysomelidae), a biological control agent for Parthenium hysterophorus (Asteraceae), in Bangalore, India

“…As in the case of Z. suturalis (Fabricius) attacking Ambrosia artemisiifolia (Asteraceae) in the USSR (Kovalev, 1988), Z. bicolorata defoliates Parthenium plants in a particular area and then migrates. As a result, by the end of the rainy season very few adults are likely to be present in the initial area of defoliation.…”