SEASONAL ABUNDANCE OF INSECTS OCCURRING ON RUMEX CONFERTUS WILLD., AS AN INTERESTING APPROACH TO THE USE OF BIOLOGICAL CONTROL AGENTS

Dariusz Piesik

ABSTRACT

Field research was conducted to determine insects occurring on Rumex confertus Willd. The experiments were carried out in 1997, 1998, 1999 and additionally in 2001 from April to late September. The field trials were located in the natural habitat of R. confertus on meadows near Vistula river; in Bydgoszcz (53⁰13^'N, 18⁰15^'E) and Toruń (53⁰2^'N, 18⁰61^'E) vicinities. Mossy sorrel was injured by the following pests in order of feeding impact: Mamestra dissimilis Knoch., Rhinoncus pericarpius L., Phyllobius virideaeris Laich., and Phyllobius maculicornis Germ. The losses of R. confertus biomass were recorded throughout the whole growing season until the plants desiccating. Two generations of M. dissimilis in both locations were recorded. In case of R. pericarpius and Phyllobius spp. one generation was observed.

Key words: biological control, Rumex confertus Willd., mossy sorrel, insects, Mamestra dissimilis Knoch., Rhinoncus pericarpius L., Phyllobius spp..

INTRODUCTION

R. confertus (mossy sorrel) is a widely adapted plant and one of the most dangerous weed in the world due to its reproductive potential expansion resulting from abundant seed production [4]. R. confertus occurs in new stands in Poland every year. As sorrel contains high amounts of oxalic acid when consumed in large quantities the lethal poisoning of animals can occur.

The chemical control of populations is difficult to maintain due to the rich root system that support rapid re-growth. After applying herbicides the green parts of the plant die, but shortly, new leaves emerge [18, 19]. Besides, unjustified chemical treatments can induce the breakdown of plant’s resistance [2, 9, 15].

Considering this dilemma biological control offers a potential solution in some regions for some pests [11, 22]. R. confertus is an example of the plant that is difficult to control by chemical methods and biological control might be a promising option to reduce its stands. Such insects as Mamestra spp. (Lepidoptera: Noctuidae) and Rhinoncus spp. (Coleoptera: Curculionidae) can play an important role in this approach [21].

The aim of this study was to evaluate the seasonal abundance and number of generations of M. dissimilis, R. pericarpius, Phyllobius spp. on R. confertus.

METHODS AND MATERIALS

The experiments were carried out in 1997, 1998, 1999 and additionally in 2001 from April to late September. The field trials were located in the natural habitat of R. confertus on the marshy meadows near Vistula river; in Bydgoszcz (53⁰13^'N, 18⁰15^'E) and Toruń (53⁰2^'N, 18⁰61^'E) vicinities. Those places were chosen due to their location. R. confertus plants spread along the Vistula as well as the other rivers. Sampling was continued over whole growing season at 7 and 10 day intervals in Bydgoszcz and Toruń, respectively. In Bydgoszcz the study area covered 2,000 m² with about 270 R. confertus growing plants. In Toruń the observations were performed in an area of 3,750 m² with 320 mossy sorrel plants. Those areas showed significant diversification of many grass plants. The laboratory study was conducted at Dep. of Entomology, University of Technology and Agricultu re in Bydgoszcz.

In the beginning of 1997, 1998, 1999 and 2001 R. confertus was monitored and selected for the study. Whole rosette plants were used for the observation. Twenty-five randomly chosen plants in 4 replicates were observed and labeled for farther measurement. The insects sampling was performed throughout the growing season from spring to fall. Each time 25 sweeps (in 4 replicates) were made with a sweep net, which resulted in 25 compared plants. The collected insects were put in plastic bags and used for laboratory studies or killed with few droplets of CHCL₃. Regular weekly (Bydgoszcz vicinity), and 10-day intervals (Toruń vicinity) observations allowed to determine insects feeding regularly on R. confertus plants and those that fed accidentally. Over the whole growing season observations were carried out on the biology, number of generations throughout the growing season and the occurrence of the species causing injuries on R. confertus. The sampling included al so larvae for the insect’s identification or rearing.

The analysis of variance means were separated using LSD Tukey’s test.

RESULTS

Bydgoszcz vicinity study.

M. dissimilis (Lepidoptera: Noctuidaea) is a moth with wingspan from 35 to 40 mm. Thorax, head and forewings are brownish, and hind wings brighter at a front wings.

The feeding of caterpillars on R. confertus decreased the assimilation leaves area. M. dissimilis adults were active at night but sampling was performed during a day. Consequently, the seasonal abundance (Fig. 1) shows only the changes in the density of the caterpillars.

There were two generations within the growing season. The development of the first generation was recorded in June. In 1997, the population was less numerous compared to the following years. The second generation of the moth was less abundant. The caterpillars occurred after mid-July and stayed on plants until the beginning of September. The largest number of individuals was recorded in 1999. It might mean that adjustment of the insects to environmental conditions has occurred and the sorrel plants have become an attractive source of food.

R. pericarpius (Coleoptera: Curculionidae) was another species in relation to R. confertus. Data show that R. pericarpius colonized the sorrel plants. The length of adult insect is from 2 to 2.5 mm. The body is covered with scales, with white lines along the prothorax, and visible distinctive white spot.

The R. pericarpius occurrence was similar in 1998 and 1999 (Fig. 2) and was less numerous in 1997 and 2001.

Insects occurred on plants for two months. After copulation, beetles laid eggs, however, no larvae were found after hatching. Probably, they fed in soil and their density was low. The lack of a second peak in numbers suggested that beetles did not emerge for feeding after metamorphosis, but stayed in soil until the next growing season.

Also other two species of Curculionidae were recorded; P. virideaeris and P. maculicornis. The first species is generally a little smaller with length 4.0-5.0 mm. The antennae and legs are red-yellowish. P. maculicornis is 6.0 mm long and its legs are also reddish, but they darker near the tibia tip. They occurred in May and the first peak of their abundance was recorded in mid-May (Fig. 3). They fed mostly on the young plants of R. confertus. Mossy sorrel development was not restricted due to the injuries caused by larvae. They developed on roots but other plant species.

The overwintering and the summer generation of adults were the most abundant in 1997 (5 and 11 individuals on 25 examined plants, respectively). In 1998, 1999 and 2001 were less favorable for the leaf weevil’s development. The summer generation colonized the plant at the end of July and the beginning of August. After feeding, the insects dropped to the soil for overwintering.

Toruń vicinity study.

In Toruń vicinity, the first generation of moths developed after overwintering of M. dissimilis pupae. Dark white eggs were laid in mass of 30-40. The emerging larvae fed holes in these leaves and reminded aggregately, caused large injuries. The seasonal abundance of caterpillars was similar to those in Bydgoszcz. The larval development of the generations occurred in June in 1998 and June and July in 1999 and 2001 (Fig. 4).

There were few caterpillars recorded in the first year of observations, while in 1999 and 2001 their number was larger. The second generation’s development took place at the end of July and first ten days of September. In 1999, there were more caterpillars counted.

R. pericarpius left its overwintering site in first ten days of May (Fig. 5) and was observed on the plant until mid-June in 1998 and a little longer in 1999 and 2001. At the beginning of May six adults were captured in 1999. At the same time in 1998 two less individuals were observed.

The population of Phyllobius leaf weevils in Toruń increased in 1999 (Fig. 6). At the beginning of June four adults were caught while in 1998 only two individuals were captured. The summer generation developed from July to August in both years and their numbers were higher in 1999 and 2001. To compare to Bydgoszcz vicinity leaf weevils occurred later.

Over twice more caterpillars of M. dissimilis were captured in Bydgoszcz vicinity to compare to Toruń (Table 1).

Similar tendency was observed for Phyllobius spp. Also, over twice more individuals were gathered. In case of R. pericarpius no significant differences between two locations were observed. In 1999 in Bydgoszcz vicinity the highest number of M. dissimilis and R. pericarpius were observed; 74,5 and 20,8 respectively. Beetles of Phyllobius spp. were the most abundant in 1997. In Toruń the highest number of individuals for all investigated insects were recorded in 1998.

DISCUSSION

Historically, biological control has been considered an environmentally safe approach to pest control. Biological control has been the most successful control strategy against invaders and is currently the curative control measure of choice against environmental weeds, owing to its effectiveness, low cost and relatively high environmental safety [6].

Increased trade, changes in agricultural practices, and greater efforts in environmental protection may lead to an increased demand for biological control introductions [7]. In biological control, exotic natural enemies often are introduced from one place to another to effect pest suppression. This is based on the premise that discovering, importing and colonizing natural enemies that occur where an insect is not considered a pest will bring it under control in the country of introduction [8].

The positive benefit–cost ratios for many projects indicate the effectiveness of classical biological control, and in some cases, indicate high economic viability. Despite benefit–cost ratios have become increasingly important in describing the success and potential of the biological control method [16]. Control options, including mechanical removal or herbicide applying for some weeds are limited [17].

Biological agents of mossy sorrel can play an important role in controlling sorrel density. Larvae and adults feeding of individual species caused significant injuries. The moths from Mamestra spp. impacted the vegetative parts of the R. confertus plant. According to some researchers the decrease of blade surface caused by Mamestra larva feeding significantly reduced the photosynthesis processes [1, 3, 14]. On the sorrel plants, also Phyllobius spp. were recorded. The adults attacked leaves, buds and pedicles, while the larvae fed on roots. Lerenius and Janson [12], Maceljski and Igrc [13], as well as Rougon et al. [20] have described feeding of adults and larvae of Phyllobius spp. on sorrel, indicating those insects as interesting for biological control.

Some other weevils have the potential for biological control. During the 1960s and 1970s, two species of weevils, Rhinocyllus conicus Froelich and Trichosirocalus horridus (Panzer), were imported into the United States and Canada as classical biological control agents of musk thistle [10]. Larvae of T. horridus feed in the plant crown, which often results in the production of multiple flower stems. R. conicus may attack flower heads. Larval feeding in the receptacle causes the abortion of developing ovules, as well as the destruction of young achenes [10]. As a result, the production of high quality seed may be reduced by as much as 78%. Also the Asian weevil Rhinoncomimus latipes Korotyaev, may be considered as potential biological control agent of Polygonum perfoliatum L. [5].

CONCLUSIONS

1. Mossy sorrel (R. confertus), a weed of the polygonum family (Polygonaceae), was injured by following pests in order of feeding impact: M. dissimilis, R. pericarpius, P. virideaeris and P. maculicornis. The feeding was noted over the whole growing season.

2. There were two generations of M. dissimilis; one of Phyllobius spp. and one of R. pericarpius in both locations.

3. The results show some possibilities to utilize those insects as a biological control agents to reduce R. confertus population.

1. Benuzzi M. and Antoniacci L., 1995. Recent successes in biological and integrated control strategies on strawberry. Rivista di Frutticoltura e di Ortofloricoltura 57(6): 63-65.

2. Boczek J. 1996. Stan i perspektywy walki biologicznej z chwastami [State and perspectives of biological control of weeds]. Post. Nauk Roln., 4, 77-89 [in Polish].

3. Borisova I.P. and Klochkova E.G., 1995. Experience in rearing lepidopterous insects on artificial nutrient media. Zasz. Rast. 2: 7.

4. Cavers P.B. and Harper J.L., 1964. Biological flora of the British Isles, Rumex obtusifolius L. and Rumex crispus L. Ecol. 52: 737-766.

5. Colpetzer K., Hough-Goldstein J., Ding J. and Fu W., 2004. Host specificity of the Asian weevil, Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae), a potential biological control agent of mile-a-minute weed, Polygonum perfoliatum L. (Polygonales: Polygonaceae). Biol. Control 30: 511–522.

6. Crutwell-McFadyen R.E.C., 1998. Biological control of weeds. Annu. Rev. Entomol. 43: 369–393.

7. De Nardo E.A.B. and Hopper K.R., 2004. Using the literature to evaluate parasitoid host ranges: a case study of Macrocentrus grandii (Hymenoptera: Braconidae) introduced into North America to control Ostrinia nubilalis (Lepidoptera: Crambidae). Biol. Control 31: 280–295.

8. Gerling D., Rottenberg O. and Bellows T.S., 2004. Role of natural enemies and other factors in the dynamics of field populations of the whiteflyy Siphoninus phillyreae (haliday) in introduced and native environments. Biol. Control 31: 199–209.

9. Jędruszczak M. 1998. Niektóre ekologiczne skutki ochrony przed chwastami [Some ecological results of weeds control], Puławy, 78-84 [in Polish].

10. Kok L.T., 2001. Classical biological control of nodding and plumeless thistles. Biol. Control 21: 206-213.

11. Kovalev O.V. and Zaitzev V.F., 1996. A new theoretical approach to the selection of promising agents for biological weed control. Proc. IX Int. Symp. Biol. Contr. Weeds, Stellenbosch South Africa, 283-285.

12. Lerenius C. and Jansson J., 1995. Leaf weevils damage grassland on light soils. Vaxtskyddsnotiser 59(1): 1-5.

13. Maceljski M. and Igrc J., 1990. The phytophagous insect fauna of Ambrosia artemisiifolia. Proc. VIII Int. Symp. Biol. Contr. Weeds, Lincoln University, Canterbury, 639-643.

14. Maini S. and Burgio G., 1990. Biological control of Ostrinia nubilalis (Hb.) (Lepidoptera:Pyralidae) on protected pepper. Bollettino dell’Istituto di Entomologia ’Guido Grandi’ della Universita degli Studi di Bologna 44: 23-36.

15. Marocchi G., 1989. New Problems in weed control in Italy. Proc. VII Int. Symp. Biol. Contr. Weeds, Rome Italy, 633-637.

16. McConnachie A.J., de Wit M.P., Hill M.P. and Byrne M.J., 2003. Economic evaluation of the successful biological control of Azolla filiculoides in South Africa. Biol. Control 28: 25–32.

17. McConnachie A.J., Hill M.P. and Byrne M.J., 2004. Field assessment of a frond-feeding weevil, a successful biological control agent of red waterfern, Azolla filiculoides, in southern Africa. Biol. Control 29: 326–331.

18. Piesik D. 2000. The occurrence of Gastroidea viridula Deg. and Gastroidea polygoni L. on Rumex confertus Willd. as biological representatives of weed population control. J. Plant Prot. Res. 40(3): 219-230.

19. Piesik D. 2001. The occurrence of Hypera rumicis L. (Col., Curculionidae) on Rumex confertus Willd. as an interesting opening for biological weed population control. J. Plant Prot. Res. 41(3): 209-215.

20. Rougon C., Roques A., Rougon D. and Levieux J., 1995. Impact of insects on the regeneration potential of oaks in France. Action of phyllophagous Curculionidae (Coleoptera) on female flowers prior to fecundation. J. Appl. Entomol. 119(7): 455-463.

21. Spencer N.R., 1980. Exploration for biotic agents for the control of Rumex crispus. Proc. Int. Symp. Biol. Contr. Weeds, Brisbane, Australia 1980, 125-151.

22. Watson A.K. and Wymore L.A., 1989. Biological control, a component of integrated weed management. Proc. VII Int. Symp. Biol. Contr. Weeds, Rome Italy, 101-106.

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