The honeybee (Apis mellifera L.(Hym.: Apidae)) as a potential host of Teretriosoma nigrescens Lewis (Col.: Histeridae), predator of the Larger Grain Borer

Contents - Previous - Next

G.-A. Laborius and D. Mautz
GTZ, Hamburg, Germany and Bayerische Landesanstalt für Bienenzucht, Erlangen, Germany

INTRODUCTION

Teretriosoma nigrescens is the most effective antagonist of the Larger Grain Borer identified to date. Ecological studies performed by different investigators indicate that it is well adapted to its host (Boeye et al. 1988, 1989, Leliveldt et al. 1989, Rees 1985, 1987, 1990). Nevertheless it is necessary to clarify whether it is able to extend its predatory range from its original host to other insect species, in particular to beneficial insects such as honeybees. General observations in Central America indicate that predation of the honeybee brood seems to be unlikely. Farmers often place their beehives under the eaves of their maize store in the immediate vicinity of the predator. In 35 years of experience in the institute of Apiculture of the University of Costa Rica, Ramirez (1990) has not observed a host-prey relationship between the two insects.

The experiments described here address the question of whether T. nigrescens might prey on Apis mellifera carnica under laboratory and flight room conditions.

MATERIALS AND METHODS

Two different test series were investigated:

• Laboratory tests in petri-dishes with close contact between prey and host in the Federal Bavarian Institute of Beekeeping in Erlangen.
• Tests in the bee flight room under semi-practical conditions in the Institute of Apiculture of the University of Frankfort, Oberursel.

1. Laboratory tests

The investigations comprised five experimental groups. Four groups tested the response of T. nigrescens to the developmental stages of the honeybees and one group consisted of mixed developmental stages. In each group predatory effects of both larvae and adults of T. nigrescens were tested and in one trial per group the predator had the choice between A. mellifera and P. truncatus.

All trials were conducted in the absence of adult bees.

Group 1: A piece of comb containing 10 eggs of A.mellifera was exposed to T. nigrescens. The comb had to be replaced every two days. The whole experiment lasted one week.

Group 2: 10 young larvae (L1 - L2) in pieces of comb were exposed to T. nigrescens for one day (whole experimental time - one week).

Group 3: 10 older larvae (L4- L5) were exposed to T. nigrescens for one day (whole experimental time - one week).

Group 4: 10 pupae in sealed brood cells were given to T. nigrescens for one week.

Group 5: The mixed group included 10 A. mellifera eggs, 5 young larvae, 5 older larvae and 5 pupae. Eggs and larvae were replaced every day for one week.

In the control set-up all individuals were kept separately. The number of repetitions per trial varied and may be seen in Table 1.

All trials were incubated at 28°C and 70% r.h. Group 1-3 and 5 were inspected on a 2-3 hourly basis, Group 4 was observed twice a day. The behaviour of T. nigrescens and its effects on the different developmental stages of A. mellifera were studied.

2. Tests in the bee flight room

The colony of the bee race Apis mellifera carnica was kept in a flight cage of 2m x 3m in area and 2,5m in height. The colony consisted of about 15-20,000 worker bees and one queen. During the experiments the colony was continuously rearing broods, so large numbers of eggs, larvae and pupae were present in the bee hive. For experiments inside the colony an observation hive (Frisch, 1965) was used.

The bees were fed with sugar syrup ad libitum. Freshly ground pollen was offered twice a day.

The bee flight room had a constant temperature of 28±1.2° C and a relative humidity of 65± 3%. The room was illuminated by incandescent bulbs (type Philips TT L 05) which had a frequency of 300 Hz. The light-darkness cycle was set to 13h light and 11h darkness.

In both test series, the T. nigrescens used were from the rearing colonies at the Federal Biological Research Centre for Agriculture and Forestry (BBA) in Berlin. The country of origin was Costa Rica.

RESULTS

1. Results of the laboratory tests

In the set-up where adults or larvae of T. nigrescens had the choice between A. mellifera brood in combs and P. truncatus eggs and larvae in maize, T. nigrescens clearly preferred the eggs and larvae of P. truncatus

Only two out of 50 eggs (Table 1, group 1) were damaged by 25 adults of T. nigrescens. One was crushed in the comb, the other was eaten. Two eggs of a total of 40 were damaged by 20 larvae of the predator. The control set-up showed that the eggs are very susceptible if they are not regularly tended to by the worker bees. 70% had died after two days.

Predation of T. nigrescens larvae or adults on young larvae (Table I, group 2) of A. mellifera was not found. The mortality of the young larvae in the control was very high. 40% had died after one day and 60% after two.

Predation on older larvae (Table 2, group 3) of A. mellifera was only found in trials with T. nigrescens larvae. Three of the 80 larvae in total were injured by 40 larvae of T. nigrescens. In the control setup 60% of the A. mellifera larvae died after two days, 40% after three days.

Fifty T. nigrescens adults damaged 13 out of 100 pupae (Table 2, group 4) of A. mellifera. This only occurred if the cells had been opened. Pupae in undamaged combs were never harmed by T. nigrescens. In one trial where 50 T. nigrescens adults and P. truncatus had been put together with 100 pupae, two pupae were damaged. The sealed cells had been opened by adults of P. truncatus The larvae of T. nigrescens were not seen to prey on pupae of A. mellifera.

In the mixed group (Table 3, group 5) 70 adults of T. nigrescens damaged one of 35 pupae of A. mellifera 40 larvae of the predator injured two out of 20 older larvae of A. mellifera. The mortality in the control showed a lifespan for the insects similar to that of groups 14.

1.2 Behaviour of T. nigrescens larvae.

T. nigrescens larvae did not show any particular searching behaviour for A. mellifera in the experimental environment. In some cases (7%) they were trapped on the combs in traces of honey or they were found «drowned» in larval food in the cells (4%). Within three to four days most of the larvae died and had to be exchanged in the experiments.

1.3 Behaviour of T. nigrescens adults.

At the beginning of the tests T. nigrescens adults ran aimlessly about the test chamber for about 2 hours. Later they mainly remained on or under the combs. They did not show any particular interest in the A. mellifera brood. In the control set-ups without any food, no mortality was observed after one week.

Table 1: Number of development stages of Apis mellifera (A.m.) injured per repetition (rep.) by Teretriosoma nigrescens (T.n.), (P.t. = Prostephanus truncatus), Erlangen, 1989 groups 1 and 2

Table 2: Number of development stages of Apis mellifera (A.m.) injured per repetition (rep.) by Teretriosoma nigrescens (T.n.), (P.t. = Prostephanus truncatus), Erlangen, 1989 groups 3 and 4

Table 3: Number of development stages of Apis mellifera (A.m. ) injured per repetition (rep.) by Teretriosoma nigrescens (T.n.), (P. t. = Prostephanus truncatus), Erlangen, 1989 group 5

2. Results of tests in the bee flight room

2.1 Invasion of the bee colony by T. nigrescens.

2.1.1. Trials to ascertain whether the potential predator is able to enter the bee hive by phoresy.

T. nigrescens was placed on the feeding dish at which bees collected food. Adults and larvae did not move towards the bees. Specific reactions or behaviour of bees towards T. nigrescens were not noticed. In several experiments a beetle was placed on a tethered bee, but in many cases it subsequently left the bee. The beetle was not able to cling to a flying worker bee. As a result of these observations, transportation and invasion of the bee colony by phoresy seem to be impossible.

2.1.2. Experiments at the hive entrance

Single adult beetles were placed at a distance of 2 cm from the front of the hive entrance (in total the movement of 93 beetles were observed). On average the beetles remained only 12 seconds on the platform. In most cases they ran away from the entrance. No T. nigrescens reached the interior of the hive. Guard bees reacted only in cases of direct contact of the beetles with the bee's legs. To guide the beetle to the interior of the hive a pheromone capsule of «Trunk call» (T1 + T2) was placed within the hive entrance. However, the beetles still moved away from the entrance. In these experiments the average time spent on the platform was 20 seconds. Larvae were placed at a distance of 2 cm from the entrance. In 84 experiments the larvae remained on the platform for 3.3 min. on average. The guard bees attacked the larvae and seized them between their mandibles. Some were killed and others badly injured. The bees carried the larvae away and dropped them at some distance from the hive. In particular, mobile and fast moving larvae were seized by guard bees earlier than immobile larvae.

2.2 T. nigrescens inside the bee colony.

2.2.1. Experiments on brood combs with bees.

A beetle was placed into a brood cell containing a bee larva. In a total of 70 experiments, the adult beetles stayed on the comb for 10.6 min. on average, before falling down to the floor of the observation hive. In many cases the larvae were removed from the brood cell by the worker bees. In 36 experiments they remained inside the cell only for an average of 3 min.

2.2.2. Experiments on brood combs without bees.

A beetle was placed into a brood cell beside a bee larva and observed until it started to move and tall down from the comb. On average the adult beetles (52 experiments in total) remained on the comb for 47.4 min. the larvae for 52.2 min.

2.2.3. Experiments on empty combs without bees.

Adult beetles remained an average (75 experiments in total) of 15.9 min. on the comb before they tell down; larvae 29.7 min. (34 experiments in total). in no cases was predation of the bee larvae observed.

DISCUSSION

The natural distribution of A mellifera is restricted to the Old World while T. nigrescens is found in Central America. As the habitat of T. nigrescens and A. mellifera is different, contacts and direct biological interactions are not likely to occur in natural situations. As a consequence, the results presented here are based on experimental methods where direct contact between T. nigrescens and A. mellifera was artificially brought about for research.

The experiments in the laboratory differ considerably from natural conditions. The temperature of 28° C was ideal for T. nigrescens but too low for the bee brood. It caused a higher death-rate than expected. This problem could be overcome by frequent observations and exchange of the supplied developmental stages of A mellifera.

Predation of T. nigrescens on the bee brood was extremely rare under these circumstances, and only occurred after long observation periods and without any other prey. Starving T. nigrescens showed some interest in the A. mellifera brood. Living larvae and eggs were attacked only infrequently by T. nigrescens larvae. If damaged pupae were found it was impossible to distinguish whether they had been harmed whilst alive or after their death.

In trials with young larvae of A. mellifera it was very difficult to recognize the effect of any damage because most of them died anyway within a few hours of being outside the bee hive due to starvation and low temperatures.

Although a very low level of predation by T. nigrescens on the brood of A. mellifera was observed under laboratory conditions, no particular attractivity could be established.

The experiments in the bee flight room are closer to natural conditions than those in the laboratory. The main hurdle for a predator of a bee brood is how to get into the bee hive. Various mites and parasites of bees invade the bee colony by transportation (phoresy) on foraging bees. In the case of T. nigrescens this method can be excluded because it does not seem able to cling to flying bees.

It is also unlikely that the beetle can invade the colony by its own means. The beetles regularly retreated from the hive entrance. Apparently the air current originating from the fanning bees repels T. nigrescens. In contrast to the adult beetles, larvae of T. nigrescens seem to frequently provoke defence behaviour mm the part of the guard bees.

In contrast to the laboratory experiments no predation on honeybee larvae was observed in the flight room trials. T. nigrescens adults as well as larvae are clearly not morphologically suited to remain on the combs for a long time since they fell to the floor of the hive after some time. The time spent by the larvae on the comb was shorter than that of the adult beetles if worker bees were present The reason for this difference seems to be the greater aggression of the bees towards T. nigrescens larvae.

The African races of Apis mellifera; the East African honeybee of the savannas A. mellifera scutellata and the West African A. mellifera adansonii have a very pronounced and efficient colony defence behaviour. Compared to Apis mellifera carnica used in our tests these African bees are known to be more effective in defending against predators and parasites (Ruttner, 1989). it is very likely that these bees would be much taster and probably even more effective in repelling T. nigrescens in Africa if ever the rare chance of contact between these two insect species should occur.

The negative results obtained in the flight room experiments, the little interest shown by T. nigrescens in A. mellifera and the low incidence of damage after long exposure periods in laboratory experiments under artificial environmental conditions indicate that intact colonies of A. mellifera would not be harmed by T. nigrescens.

CONCLUSIONS

In two separately conducted test series the potential predatory effect of Teretriosoma nigrescens - a specific antagonist of the Larger Grain Borer, Prostephanus truncatus - on honeybee broods was investigated.

1. In laboratory trials eggs, young and old larvae and pupae of Apis mellifera carnica were placed together with adults and larvae of T. nigrescens.
   The results of this investigation showed that the predator is not especially interested in the honeybee brood. Only in a few cases was predation of eggs, old larvae and pupae by starving T. nigrescens observed. If the predator had the choice between the young of P. truncatus and A. mellifera, the latter was never attacked.
2. The second test series was conducted under more natural conditions in a bee flight room. Experiments showed that phoresy is uncommon. No tendency of T. nigrescens adults to get into the hive using their own means could be observed. Beetles generally ran away from the hive entrance. Larvae of T. nigrescens were attacked by guard bees and carried away. No predation of the bee brood could be observed if T. nigrescens was placed in the brood cells inside the hive.

REFERENCES

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

Boeye, J., Burde, S., Keil, H., Laborius, G.-A. and Schulz, F.A. (1988) The Possibilities for Biologically integrated Control of the Larger Grain Borer (Prostephanus truncatus (Horn)) in Africa. pp 110-139 in G.G.M. Schulten and A.J. Toets (Eds.) Proc. of the Regional African Workshop on Control and Containment of the Larger Grain Borer, Arusha 16-21 May, 1988, FAO, Rome. Report 2, 209pp

Boeye, J., Leliveldt, B., Laborius G.-A. and Schulz, F.A. (1989) Evaluation of Biological Methods to Control the Larger Grain Borer Prostephanus truncatus (Horn) (Col.: Bostrichidae) in Africa with special Reference to the Predator Teretriosoma nigrescens Lewis (Col.: Histeridae). pp 939-959 (Vol. III) in Proc. DLG intern. Conf: Integrated Pest Management in tropical and subtropical cropping systems. Bad Duerkheim, F.R.G. Feb. 8-15, 1989.

Frisch, K. v. (1965) Tanzsprache & Orientierung, Springer Verlag, 637 pp.

Leliveldt, B. and Laborius, G.-A. (1990) Effectiveness and specifity of the antagonist Teretriosoma nigrescens Lewis (Col.: Histeridae) on the Larger Grain Borer Prostephanus truncatus (Horn) (Col.: Bostrichidae) pp. 87-102 in R.H. Markham & H.R. Herren (Eds.) Biological control of the Larger Grain Borer. Proc. of an IITA/FAO coordination meeting, Cotonou, Republic of Benin, 2-3 June 1989. IITA, Ibadan, Nigeria, 167 pp.

Ramirez, W.B. (1990) Private communication

Rees, D.P. (1985) Life history of Teretriosoma nigrescens Lewis (Col.: Histeridae) and its ability to suppress populations of Prostephanus truncatus (Horn) (Col.: Bostrichidae). J. Stored Prod. Res. 21 (3), 1 15 118.

Rees, D.P. (1987) Laboratory studies on predation by Teretriosoma nigrescens Lewis (Col.: Histeridae) on Prostephanus truncatus (Horn) (Col.: Bostrichidae) infesting maize cobs in the presence of other maize pests. J. Stored Prod. Res. 23 (4), 191-195.

Rees, D.P. (1990) Observations on the ecology of Teretriosoma nigrescens Lewis (Col.: Histeridae) and its prey Prostephanus truncatus (Horn) (Col.: Bostrichidae) in the Yucatan peninsula, Mexico. Trop. Sci. 30, 153-165.

Ruttner, F. (1989) Biogeography & Taxonomy of the Honeybees, Springer Verlag, 284 pp.

The silkworm (Bombyx mori L. (Lep.: Bombycidae) as a potential host of Teretriosoma nigrescens Lewis (Col.: Histeridae), predator of the Larger Grain Borer

G.-A. Laborius
GTZ, Hamburg, F.R. Germany

INTRODUCTION

In accordance with the recommendations made by the IITA/FAO Coordination Meeting in Cotonou in June 1989, before the predator Teretriosoma nigrescens can be released for the purpose of combatting the Larger Grain Borer, the lack of any damage to various beneficial insects on the part of the predator must be demonstrated. The following investigations examine the potential prey-host relationship between the silkworm and the predator concerned.

MATERIALS AND METHOD

The study was carried out at the Spinnhütte plc (Silk technology Company) in Celle, Germany.

The following stages of development of Bombyx mori were tested:

- eggs
- 1st to 4th larval stages, and
- pupae.

The trials with the adult beetles and the larvae of the predator with the various stages of development of the moth were carried out separately. In one trial per group, the predator was provided with the alternative of a Prostephanus truncatus (Horn) brood.

The trials were performed in 3 litre jars. The silkworms were constantly fed with fresh leaves from the mulberry tree (Morus alba L.). The trials were carried out at room temperatures between 22° and 26° C and all repeated three times.

Ten eggs, ten larvae from stages 1, 2, 3 and 4, and five pupae of B. mori were placed together with five adults or larvae of the predator in each trial. One of each of the individual trial groups was kept separately as a control.

T. nigrescens was taken from the rearing colonies at the Federal Biological Research Centre for Agriculture and Forestry (BBA) in Berlin. The predator's country of origin was Costa Rica.

RESULTS AND DISCUSSION

Predatory behaviour of T. nigrescens on B. mori was not recorded in any of the cases. All of the developmental stages of the silkworm used in the tests were undamaged at the end of the test period (10-14 days, depending on the stage of development). No negative influence on the development of B. mori could be demonstrate as a result of the presence of the predator in comparison to the control set-up.

There was no incidence of mortality among the T. nigrescens adults. They largely remained hidden under the leaves of the mulberry tree, or were to be found in the P. truncatus brood medium in the mixed trials.

The larvae of the predator died in the majority of cases and were dried out. The environment was evidently not suitable for them. In the mixed trials, they were to be found in the maize; the P. truncatus medium.

In the trials with pupae and cocoons of B. mori together with the P. truncatus brood, the pest beetles had eaten holes in a number of cocoons. The pupae, however, remained undamaged and the moths emerged without any ill effects.

The mortality of the T. nigrescens larvae seems to indicate unfavourable breeding conditions for the predator. However, no damage to the silkworm is to be expected even under more favourable conditions no mortality was seen in the beetles, and B. mori was not affected. It may thus be concluded that there is no predatory relationship between B. mori and T. nigrescens and that no such relationship is to be expected in the future under natural conditions.

Contents - Previous - Next