|Al-Kirshi, Abdul Gabbar Sultan: Untersuchungen zur biologischen Bekämpfung von Trogoderma granarium Everts, Trogoderma angustum (Solier) und Anthrenus verbasci L. (Coleoptera, Dermestidae) mit dem Larvalparasitoiden Laelius pedatus (Say) ( Hymenoptera, Bethylidae) |
Kapitel 6. Summary
Dermestide pests of stored products are widely distributed throughout the world. They infest stored animal and plant products and frequently cause great damage and losses. Even a wide range of materials can be damaged or destroyed by Infestation with dermestides.
The Khapra beetle T. granarium causes serious damage and losses to grain and grain products particularly in the tropics. In many countries it is listed as a quarantine pest. The importance of T. angustum as a pest in stores, in dwelling houses, in shops and in museums increased in Europe during the last decades. A. verbasci infests a variety of animal products such as wool, fur, leather, feathers etc. It is also the most important pest of insect collections in museums.
Infestations by dermestids are usually controlled by treatments with insecticides. However, insecticides may cause hazards to man and the environment. Especially in the storage of small subsistence farmers in the tropics the use of insecticides may be dangerous and their costs prohibitive. Hence, there is a need for the development of alternative methods such as biological control, an efficient component in integrated pest management.
The present study was designed to assess the efficacy of the larval parasitoid L. pedatus in controlling T. granarium, T. angustum and A. verbasci.
The parasitoid wasp has desirable characteristics to control these pests.
The following results on the biology, behaviour and the potential of the wasp were obtained:
Biological characteristics of L. pedatus
- Most egg-laying activity occurred at temperatures of 25° C and 28° C. Oviposition was not possible at 15° C and below.
- The egg-laying activity occurred at both low and high relative humidity. The average numbers of eggs laid at extremely low humidity levels below 10 % and at high humidity levels above 90 % at a temperature of 28° C were 62 ± 12,6 eggs and 25 ± 8 eggs per female, respectively (n = 4).
- At 28° C and 50 -60 % relative humidity about 80 % of deposited eggs (n = 107) developed to adults. This number indicated, by consideration of the natural mortality of the larval and pupal stages, that the eggs hatching rate higher than 80 %.
- At 28° C and 50 -60 % relative humidity the total developmental time from eggs to adults was 34,7 ± 1,8 days (n = 150)
- A mated female was able to deposit fertilised eggs for a maximum period of 14 days after copulation. After that the female produced only unfertilised eggs, developing into male wasps.
- Longevity of the female wasp increased with decreasing temperature down to 15° C and could also be prolonged by supplying the wasp with a diet of honey. The average life time of normally fed female lasted from 3 weeks at 35° C up to till 16 weeks at 20° C.
Potential of L. pedatus
- During its life span a female wasp paralysed 74 ± 20 larvae of A. verbasci compared to 44 ± 10 larvae of T. granarium.
- On average, only one third of the paralysed larvae of A. verbasci were used for Oviposition.
- The venom of L. pedatus caused 100 % larval mortality in A. verbasci and T. angustum within 3 weeks.
- The venom of L. pedatus caused only 60 % larval mortality in the Khapra beetle. The rest of the paralysed but not parasitised larvae of T. granarium survived the venomous effect after 4 to 5 weeks and continued their development to adults
- This temporarily paralysing effect on the larvae of T. granarium is also important since the pest larvae are not active and therefore cannot cause any damage during this time.
- Direct parasitisation of the host larvae through the parasitoid larvae caused 100 % mortality in all three dermestids.
- At 28° C and 50 - 60 % relative humidity a single female was able to deposit
52,3 ± 6,3 eggs on 36,8 ± 5,8 larvae or 46 ± 12,5 eggs on 23,0 ± 6,0 larvae of T. angustum or A. verbasci, respectively (n = 4).
- The average number of eggs per female wasp and day was 1,42 ± 0,2 if larvae of T. angustum were used as host (n = 15).
- The female of L. pedatus also accepted larvae which have already been paralysed by other females for its own egg-laying. This may lead to fights between females for the same host.
- The wasp was found to penetrate into wheat and successfully parasites host larvae of T. granarium in a depth of 90 cm.
- At a parasitoid : host ratio of 1 : 25, L. pedatus reduced two populations of T. granarium (Yemen field strain and culture strain of the Institute for stored Product Protection BBA Berlin) by 75 - 80 % within 6 - 8 weeks.
The observed biological characteristics of L. pedatus render the wasp a suitable agent to control T. granarium, T. angustum and A. verbasci. However, field investigations in the store are needed to verify these results.
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