Transmission of the bacteria Bacillus stearothermophilus Donk by the dried fruit beetles, Carpophilus hemipterus (L.) Steph.

The dried fruit beetle, Carpophilus hemipterus (L.) (Coleoptera : Nitidulidae), is one of the most serious stored products’ pests and destroys fruit in almost every country. Fruit such as apples, apricots, bananas, plums, peaches, oranges and grapefruit; cereals; dried fruit; seeds and other stored products have been reported to be subject to the beetle attack (Hinton, 1954 and Munro, 1966). In New Zealand, attack by C. Hemipterus is of minor importance when compared with overseas countries, especially U.S.A. Some N.Z. infestations have been serious enough to be recorded, such as the infestation of dried fruit in Christchurch during 1922 (Miller, 1922) and of prunes in storage in Dunedin during 1949 (Belton, 1950). The damage is generally caused by feeding injuries and always followed by rots which increase the damage and allow it to reach injurious levels. Various micro-organisms that are responsible for rot disease such as fungi of different genera, yeasts and bacteria have been observed to be transmitted by C. hemipterus. According to Leach (1940), the association of C. Hemipterus and rot diseases is considered to be of the non-obligatory type, since the association is not restricted to any particular type of host organism. Therefore, the spread of rot disease is very significant when this dried fruit beetle is involved. Dissemination of the disease is carried out by mechanical means through wounds made by beetles (Phillips et al, 1925) and/or by the beetles bringing the rot organisms into contact with natural openings of plants. When the mechanism of bacterial transmission on by insects is considered, there are three factors that must be considered as governing the transmitting process. These are: (a) External and/or internal contamination of the insect’s body. Insects capable of being both externally and internally contaminated are more efficient as disease carriers than those capable of being contaminated only externally, Multiplication of bacteria in internal parts such as the digestive system and faecal material are the most important factors that allow bacteria to be continuously generated and beetles to be most suitable vectors. (b) Duration of viability of bacteria on or in the insect's body. The duration of bacterial viability when the bacterium is on or in the insect's body is very important since the vector's body offers different microclimatic environments from normal natural conditions. (c) The category of the vector. The question arises as to whether or not the insect is a true non-obligatory vector which possess no restriction in carrying any phytopathogenic organisms, This is because past observations showed that there was a possibility of the beetle transmitting fungal and yeast rot, as well as bacterial rot, From the knowledge of bacterial association with vectors (see literature review, Chapter II), the conclusion can be reached that there are possibilities of C. hemipterus transmitting bacterial rot diseases under New Zealand conditions. Since there is lack of knowledge in the field of bacterial transmission, the aim of the present study was, in general, to prove the possibilities of transmission by C. Hemipterus of bacterial pathogens. This was considered to be best done specifically by examining the three important factors mentioned above and to investigate; (1) Contamination of the beetle by bacteria. (2) Duration of viability of bacteria in or on the beetle. (3) The nature of the beetle as a vector,