Ability of Teretriosoma nigrescens to survive and breed on stored product pests other than Prostephanus truncatus

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Pöschko, M., Laborius, G.-A. and Schulz, F.A.
BBA Berlin, GTZ, Hamburg and TU Berlin, Germany

ABSTRACT

The influence of the predator Teretriosoma nigrescens Lewis on the development of different pest populations was tested. The results demonstrate the preference of Prostephanus truncatus (Horn) as prey for T. nigrescens.

Nevertheless the predator is able to breed on other stored product pests such as: RHIZOPERTHA DOMINICA, DINODERUS BIFOVEOLATUS and SITOPHILUS ORYZAE. However, it is only able to suppress significantly the population increase of its preferred prey. The commodities used for feeding the pests can influence the development of the predator. T. nigrescens reduced the number of eggs of moths offered in glass dishes, but it had nearly no effect on the development of the moth populations.

INTRODUCTION

About ten years ago P. truncatus (Col.: Bostrichidae), a storage pest of maize and dried cassava was introduced into East and later West Africa (Dunstan & Magazini 1981, Harnisch & Krall 1984, Laborius et al. 1985).

The origin of P. truncatus is South and Central America where the pest population increase is successfully suppressed by its natural antagonists. The most important of these antagonists is the predator T. nigrescens (Col.: Histeridae) (Rees 1985, Böye 1988, Böye et al. 1992). Recent investigations demonstrate that T. nigrescens is very closely associated with P. truncatus In Africa, where the predator is not yet present, P. truncatus has become a pest of great importance. In Togo and Tanzania P. truncatus is widely distributed and causes high losses on stored maize and dried cassava (Pantenius 1987).

As a possible biological control agent of P. truncatus the introduction of T. nigrescens into Africa was discussed (Schulz & Laborius 1987). Before this can be realized numerous investigations are necessary to ensure that the predator poses no threat to the African environment. The following studies were carried out to investigate the ability of T. nigrescens to feed and breed on insect species other than P. truncatus

MATERIAL AND METHODS

The development of different pest populations was tested with and without the influence of T. nigrescens. The pest species were reared on commodities provided by the Federal Biological Research Centre for Agriculture and Forestry (BBA) in Berlin. Glass jars (300 ml) were filled with the different commodities (about 150g of grains, 100g rolled oats, 50g wheat bran). 100 adult pest insects and 10 newly emerged adults of T. nigrescens ( 1 -14 days) were added. Pest cultures without T. nigrescens were used as controls. Each trial was carried out with 5 replicates (n=5) at 27°C ± 1°C and 75% ± 5% r.h. in darkness. After 8 weeks the number of progeny of T. nigrescens and the final number of adult pests was counted.

Variations of these methods are outlined in the short introduction to each experiment.

RESULTS

1. Development of different pest populations with and without T. nigrescens

In the initial test 11 different pest species including P. truncatus were investigated as potential prey of T. nigrescens (with T. nigrescens: 3 replicates; without predator: 2 replicates),

T. nigrescens was able to breed only on beetles belonging to the family Bostrichidae. In each of the repetitions with P. truncatus about 10 progeny of the predator were found (in total: 22 adults and 9 larvae). In the case of R. dominica as prey three F1 larvae of the predator were found in one repetition. One T. nigrescens larva developed in the trial with D. bifoveolatus. Only the number of P. truncatus progeny was clearly reduced by T. nigrescens (84.2%). The predator had little or no effect on the development of the other pest species.

Table 1: Development of different stored pest populations in 8 weeks with and without T. nigrescens and the ability of the predator to peed and to breed on them (± SD) * 10 adult pests/trial,** larvae were counted, *** larvae were used

2. Development of T. nigrescens populations after a one week oviposition period on three different prey species

Based on the data in Table 1further specific studies were conducted with P. truncatus R. dominica and D. bifoveolatus. The prey species were kept on maize or sorghum in glass jars for 7 days. T. nigrescens was added, for oviposition, for one week only. The trials were checked after 4 months and the number of adult prey insects and the number of T. nigrescens progeny was recorded (Table 2).

T. nigrescens developed only on P. truncatus as prey (34.4 ± 9.6 adults and 3.4 ± 1.7 larvae). P. truncatus populations were again clearly reduced by the predator (55.2%).

Table 2: Development of T. nigrescens populations after an oviposition period of 7 days with different preys (+SD)

3. Ability of T. nigrescens to multiply on pests kept on various commodities

Many pest species are generally able to breed on different substrates. The breeding capability of T. nigrescens was tested on P. truncatus, R. dominica and S. oryzae following a pre-incubation time of 7 days of the pests on various commodities (Table 3).

T. nigrescens was able to breed on all three pest species offered. The ability of the predator to multiply on P. truncatus, and S. oryzae seems to be influenced by the number of pest progeny. However, T. nigrescens was only able to multiply on R. dominica kept on maize, although R. dominica it self produced many more progeny if kept on sorghum. Again it could be demonstrated that only the number of P. truncatus progeny was clearly reduced by the predator (78.3%, 50.7% 27.2% on maize, sorghum and wheat, respectively).

Table 3: The ability of T. nigrescens to multiply in 8 weeks on pests kept on various commodities (±SD), *all P. truncatus were dead

4. Development of the progeny of different Sitophilus species and subspecies with and without T. nigrescens

The adult pests were kept on food for oviposition for one week, before adult T. nigrescens were added. The number of adult pests was counted after 6-7 weeks (Table 4).

T. nigrescens is not able to suppress the development of any Sitophilus population. Only one larva of the predator was found in a sample with S. granarius granarius.

Table 4: Effect of T. nigrescens on the development of the population of different Sitophilus species and subspecies after 6-7 weeks

5. Influence of the predator T. nigrescens on the development of moth populations of different species

Fifty eggs (<1 day old) of different moth species were put on wheat bran (about 20g) or wheat grains (about 50g) in glass jars. Ten adult T. nigrescens were added to each sample. The number of adult moths was recorded after 5-6 weeks (Table 5).

In comparison with the control, T. nigrescens had only a minor effect on the number of moths when placed with the eggs of these species. In the case of Ephestia cautella no influence could be detected.

Table 5: Influence of T. nigrescens on the development of moth populations after 5-6 weeks (started with 50 eggs(±SD))

6. Influence of T. nigrescens on moth eggs offered to the predator without any other food.

Twenty eggs (<1 day old) were put in glass dishes (diameter 5cm) and two adult T. nigrescens, previously kept on maize for 2-3 weeks, were added. The number of undamaged eggs was counted after 24 hours (Table 6).

Beetles damaged or consumed on average 4-7 eggs of E.elutella, E.kuehniella and P.interpunctella while all eggs were undamaged in the control samples. T. nigrescens had less of an effect on eggs of the species C.cephalonica and E. cautella.

Table 6: Influence of T. nigrescens on the number of undamaged pest eggs, out of 20 (24 hours test (n=5))

DISCUSSION

The results show that a considerable number of replicates per trial are necessary 10 get a clear picture of the host specificity effects of T. nigrescens. This is demonstrated by differing results of the breeding ability of T. nigrescens on S. oryzae cultures in the first trials done as compared to the results given in Table 3.

Although T. nigrescens is able to breed on pest species other than P. truncatus the results make clear that P. truncatus is the preferred prey of the predator. In all trials the number of T. nigrescens progeny was higher on P. truncatus than on the other hosts presented. Even if the breeding conditions for P. truncatus itself were not optimal, e.g. on wheat, T. nigrescens was still able to replicate on it.

When T. nigrescens was kept for 7 days on cultures of various Bostrichidae, only in the case of P. truncatus was the predator both able to lay eggs and to have them hatch successfully. It was surprising to see that compared to other Bostrichidae only the final number of P. truncatus progeny was clearly reduced by T. nigrescens. Although T. nigrescens was also able to multiply on R. dominica, the number of host progeny was not reduced compared to the control (Table 3). Since T. nigrescens is not able to breed in the absence of prey, on plant materials alone (Pöschko et al. 1992, Rees 1990), it seems that the predator must have consumed eggs and larvae of R. dominica. A possible explanation might be that R. dominica is able to compensate the losses by an increased egg production or that T. nigrescens killed more P. truncatus individuals than were necessary for feeding and reproduction. The explanation that T. nigrescens needs more host individuals of P. truncatus than those of the smaller R. dominica seems to be unlikely.

Although T. nigrescens can feed on the eggs of several stored product Lepidoptera it seems doubtful that there is any egg searching mechanism. Instead it seems that T. nigrescens finds the food sources accidentally whilst walking through the substrate. Further data can be found in the publication of Leliveldt ( 1989) who used eggs of different Coleoptera. Within 24 hours T. nigrescens consumed 5.5 ± 1.2 eggs of T. castaneum and 6.4 ± 1.8 eggs of S. oryzae if given in small glass dishes. Under the same conditions the predator consumed 5.7 ± 2.0 eggs of P. truncatus. But in contrast to the development of P. truncatus T. nigrescens had only limited effect on the population increase in T. castaneum and S. oryzae kept on maize.

T. nigrescens only replicated on R. dominica when the pest was kept on maize. Linking the present data with the proven ability of T. nigrescens to feed on maize (Pöschko et al. 1992) and its preference for maize found in the free choice test (Rees 1990) it is clear that apart from the host insect, the plant substrate also plays an important role in the survival and the development of the predator.

Summarising au of the data, it can be said that T. nigrescens is a host specific predator of P. truncatus.

REFERENCES

Böye, J. (1988) Autökologische Untersuchungen zum Verhalten des Großen Kornbohrers Prostephanus truncatus (Horn) (Col.: Bostrichidae) in Costa Rica. Dissertation, Institut für Phytopathologie der Christian-Albrechts-Universität zu Kiel, 195 pp.

Böye, J., Laborius, G.-A. and Schulz, F.A. (1992) The response of Teretriosoma nigrescens Lewis (Col.: Histeridae) to the pheromone of Prostephanus truncatus (Horn) (Col. Bostrichidae). Anz. Schädlingskde., Pflanzenschutz, Umweltschutz (in press)

Dunstan, W.R. and Magazini, I.A. (1981)0utbreaksandnew records. Tanzania. The Larger Grain Borer on stored products. FAO Plant Protection Bulletin, 29 (3/4), 80-81.

Harnisch, R. and Krall, S. (1984) Togo: Further distribution of the Larger Grain Borer in Africa. FAO Plant Protection Bulletin, 32, 113- 114.

Laborius, G.-A., Leliveldt, B. and Keil, H. (1985) Der Große Kornbohrer, Prostephanus truncatus (Horn). Ein neuer Vorratsschädling in Afrika. Der praktische Schädlingsbekämpfer, 37 (9), 179-186.

Leliveldt, B. and Laborius G.-A. (1989) Effectiveness and specificity of the antagonist Teretriosoma nigrescens Lewis (Col.: Histeridae) on the Larger Grain Borer Prostephanus truncatus (Horn) (Col.: Bostrichidae). pp 87- 102 in Markham R.H. and Herren H.R. (Eds.) Biological control of the Larger Grain Borer 1990. Proceedings of an IITA/FAO Coordination Meeting in Cotonou/Benin, 2-3 June 1989.

Pantenius, C. (1987) Verlustanalyse in kleinbäuerlichen Maislagerungssystemen der Tropen, dargestellt am Beispiel von Togo. Dissertation, Institut für Phytopathologie der Christian-Albrechts-Universität zu Kiel, 249 pp.

Pöschko, M., Laborius, G.-A. and Schulz, F.A. (1992) The significance of plant materials for nourishment and development of the predator Teretriosoma nigrescens. This publication.

Rees, D. P. (1985) Life history of Teretriosoma nigrescens Lewis (Col.: Histeridae) and its ability to supress populations of Prostephanus truncatus (Horn) (Col.: Bostrichidae). J. stored Prod. Res. 21, 115-118.

Rees, D. P. (1990) Ecology and predatory ability of Teretriosoma nigrescens Lewis (Col.: Histeridae), a potential bio-control agent for Prostephanus truncatus (Horn) (Col.: Bostrichidae). in Proc. of the 5th International Working Conference on Stored-Product Protection, 9-14 September 1990, Bordeaux (in press)

Schulz, F.A. and Laborius, G.-A. (1987) Strategy for bio-integrated control of Prostephanus truncatus (Horn) (Col.: Bostrichidae). pp 479-503 in E. Donahaye & S. Navarro (Eds.) Proc. of the 4th international Working Conference on Stored Product Protection, Tel-Aviv, Israel, 21 -26 September 1986.

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