Compost and Soldier fly larvae * To: compost@listproc.wsu.edu * Date: Tue, 2 Sep 1997 15:19:12 -0800 ------------------------------------------------------------------------ Hello again, I sent the paper as an attachment because it doesn't contain any figures or graphs, so it would be easy to decode. However, I realize that some people may still have problems opening it, so here (below) is the text version, but it is a fairly big file and I wonder if some of you may have difficulties with it. If so, I apologize in advance. I hope you enjoy it. Jerome ================================================================================ USE OF SOLDIER FLY LARVAE IN ORGANIC WASTE MANAGEMENT Dr. R. Newby Biology Department, Central Queensland University ROCKHAMPTON 4702 ABSTRACT The black soldier fly Hermetia illucens is a cosmopolitan non-pest species which occurs naturally in decomposing vegetation. This project investigated the potential for using soldier fly larvae in compost systems to hasten the breakdown of organic waste and so contribute to theoverall management of organic waste. Laboratory studies documented the response of the larvae to environmental parameters including temperature, relative humidity, pH and diet. Field trials were carried out in central Queensland to assess the acceptability and suitability of soldier fly larvae in domestic compost systems. The larvae are voracious feeders well adapted to tropical environmental conditions. It is proposed that their use could reduce significantly the amount of organic material in the waste stream destined for landfill sites. The potential of these systems in waste management in island communities is being explored. INTRODUCTION Soldier fly larvae (Family Stratiomyidae) are commonly found in association with damp habitats with a high content of decomposing vegetation. The most notorious soldier fly is the pest species Inopus rubriceps (previously Altermetoponia rubriceps) which attacks sugar cane and pasture. The stratiomyid we have been investigating is the black soldier fly Hermetia illucens. This is a cosmopolitan species which occurs naturally in a wide range of habitats but has never been recorded as a pest or even a nuisance. Our interest in this species arose from a search for methods for minimising organic waste transfer to landfills. Some estimates put the food scraps and garden waste components of domestic waste as high as 50%. Not only are landfill sites effectively nonrenewable resources but their operation is becoming increasingly expensive. Rockhampton City Council has a well established program for recycling and for minimising landfill requirements however it was recognised that there was still a significant volume of material that could be treated by alternative methods. If organic wastes can be dealt with effectively and efficiently off-site it will represent a significant saving. There are also many island tourist resorts in Queensland where waste disposal by landfill is simply not acceptable either on environmental or aesthetic grounds. There is therefore understandable interest in recycling and waste minimisation. Earthworms had been trialed previously but for various reasons, including the hot dry conditions in central Queensland, they were found to be of limited success. The adults of the black soldier fly (H. illucens ) have a superficial resemblance to wasps and this is enhanced by two semi-transparent areas on the abdomen. The adults are approximately 15 mm long (wingspan 20 mm) and are rarely seen since they appear to select darker, heavily vegetated habitats. The larvae of H. illucens typically feed on rotting vegetation and are robust animals which grow up to 20 mm in length. The final larval stage enters a nonfeeding pupal stage and weighs approximately 350 mg. This species has been used for some years in the United States for the breakdown of poultry manure (see Axtell and Arends 1990 for review). Although little is known about the biology of the species we believed it had a number of characteristics which could be exploited to maximise the efficiency of domestic compost systems and hence minimise landfill requirements. In particular we were interested to see if it could be used as an alternative to or in association with earthworms. AIM The aim of the project was to investigate the biology of the black soldier fly with an emphasis on those parameters which would permit an assessment of its potential in compost systems in Central Queensland. The project was carried out in two phases: * An initial laboratory phase investigated some of the physiological characteristic of the larvae with a view to establishing the environmental conditions required to optimise performance in compost systems. * The second phase was a field trial in cental Queensland, designed to evaluate the acceptability and effectiveness of compost systems based on soldier fly larvae. PROCEDURES Laboratory Studies Small scale laboratory experiments were conducted to assess the effects of a range of environmental parameters on the feeding rates and survival rates of larvae at different stages of development. Trials typically involved replicate sets of 10 size matched larvae kept in small plastic containers in controlled conditions. Parameters investigated included: * temperature * food composition * relative humidity * pH Field Trials Fourty five compost bins inoculated with larvae from stock cultures were set up in the Rockhampton and Yeppoon areas of Central Queensland. The trial bins were the RELN 225L Compost Bins. These were selected only because they were readily available and already in use in the Livingstone Shire area. Householders were given basic instructions and asked to keep records of the volume of waste being put in the system. The bins were inspected at monthly intervals between November 1996 and June 1997. In addition a smaller trial was set up using a number of different types of containers of varying sizes and constructions including a number of commercially available compost bins and the RELN Worm Factory. RESULTS The larvae at all stages are voracious feeders. The optimum temperature for food consumption is 35 C. Food consumption rates fall with decreasing temperature and effectively reach zero at 15 C. The larvae become inactive at temperatures less than 10 C but will survive temperatures as low as 0 C for up to 4 hours. Larvae survive at temperatures up to 45 C. The larvae become inactive at temperatures higher than 45 C and survival rate falls rapidly at temperatures over 47 C. The larvae tolerate saturated conditions well but large larvae lose weight at approximately 1% per hour at 75.5% relative humidity. As expected, the rate of water loss increases with decreasing relative humidity. Smaller larvae are more susceptible to water loss, losing approximately 1.5% body weight per hour at 75.5% RH. While the larvae consumed all types of vegetable foods (both natural and processed) they had a limited ability to remove animal products (meat and fat) even when these represented less than 10 percent of the food available in the laboratory. The larvae tolerate a wide range of pH and will survive well in compost derived exclusively from decomposing citrus fruits. This finding is consistent with published data where one species of Stratiomyidae was found in water at pH 5.7 (Brues 1928). Data from the field trials has yet to be analysed in detail but the following comments outline the qualitative findings. Preliminary results suggest a high rate of acceptance by people trialing the system. When expressions of interest were called for participants in the project, there was a much larger response than expected. Trial bins were not allocated randomly but sites were selected so as to give a good cross sectional representation in terms of family size, location, availability of backyard fruit trees etc. In general the systems were successful. All continued to function well during heat wave conditions in January 1997. In the final inspection (June 1997) nine of the 45 general trial bins were without larvae. In quite a few instances this was traced to inadequate input of scraps due to the householders having been on holidays or to them simply having fewer fruit and vegetable scraps in the winter months. Several systems failed to be self sustaining during the course of the trial. In general these could be traced to people allowing the system to dry out or not following the suggested protocols. The systems were not self sustaining in instances where the following were added in large quantities: * putrescible wastes * dried grass clippings * sawdust * soil. Adult soldier flies were not reported to be a nuisance by any in the main trial. There was only one instance of a system causing an adult fly problem and this was where a preschool group had located the system close to the door of a building. Casual observations suggest that birds may be attracted to the vicinity of bins to feed on the adult flies. DISCUSSION The soldier fly larvae were shown to be remarkably tolerant for a wide range of environmental parameters. They thrive in hot wet conditions and are such voracious feeders that in most systems the amount of by-product is quite small. Of particular importance was the fact that they can survive in the hot dry conditions common in central Queensland throughout much of summer. In this regard they are more robust than earthworms which had previously been trialed in central Queensland. The larvae will not survive prolonged dry conditions. These results were consistent with the results from the field trials where in general the soldier fly populations were self sustaining in most systems which were kept moist. Fatchurochim et al (1989) found that the maximum development rates for soldier flies in dung occurs at 70 % moisture levels. In our studies, field populations were not self sustaining in systems which dried out or where the input of food was inadequate. The oviposition of H. illucens has been investigated by Booth and Sheppard (1984). The adult females lay egg masses of 500 to 1000 eggs in sites above rotting vegetation. Our observations suggest that soldier fly populations will readily establish self-sustaining colonies in closed or semi-open compost systems. Hoy (pers comm) suggests that adults avoid oviposition sites thatare anaerobic. During January 1997 there were reports of soldier fly larvae invading worm farms. Investigations revealed that first instar larvae sought out decomposing material after hatching from eggs layed near the ventilation ports of the worm farms. We have yet to systematically investigate competition between earthworms and soldier fly larvae but preliminary results suggest the latter would outcompete the earthworms for food. The larvae take one to several months to develop depending on temperatures. One of the characteristics of the soldier fly larvae which makes them attractive from a public health point of view is that they are quite aggressive and seem to out-compete other fly species. Soldier fly have been recommended in the poultry industry specifically for the control of two species of house fly (Bradley and Sheppard 1984, Sheppard 1983). Although we made no mention of this to those involved in the trial, several people reported fewer domestic flies after they began using soldier flies. The field trials revealed ambiguous results regarding the ability of soldier fly to handle putrescible wastes. While the laboratory investigation suggested the larvae had a limited ability to deal with animal products, several people in the trial 'experimented' with their system by adding meat or fat. These results suggest that large populations of the animals are able to handle some meat products but in general the quantity used should be small and only done on an infrequent basis. In addition to the domestic trials several systems were set up at commercial kitchens and kindergartens. Two trials set up at commercial kitchens were not successful largely because there was inadequate control over the sorting of waste, particularly putrescibles. Those systems which were successful typically had an individual who was interested in the success of the system and monitored the input. The field trial has now been extended to several kindergartens in Rockhampton and a tourist operation on Great Keppel Island. Three Environmental Health Departments in central Queensland are planing a more extensive field trial of soldier fly compost systems. Because of the cost of transport, there is no intention to set up a central composting facility, however domestic composting will be encouraged. The criterion for success will be if the quantity of organic waste coming to the landfill sites can be further reduced by composting. CONCLUSIONS The black soldier fly H. illucens has larvae which are suitable for augmenting compost systems in tropical areas. The larvae tolerate a wide range of environmental conditions and are voracious feeders, particularly at higher temperatures. The larvae reduce the incidence of other flies in compost systems. The adult flies have not been recorded to be a problem and may well serve as a food source for native birds. The overall aim of the project was to evaluate soldier fly compost systems so as to be able to recommend on the optimum conditions. This has been achieved and the information willbe incorporated into promotional materials. Quite apart from its application to domestic situations, we believe the use of soldier fly larvae offers considerable potential for the management of waste in island and tourist communities. There is a need to extend this study by systematically investigating the best construction for compost bins for soldier fly based composting. The next phase of the investigation will be to evaluate the effectiveness of the systems in small communities such as schools and island and tourist resorts and to systematically compare soldier fly systems with vermiculture. ACKNOWLEDGMENTS Financial support for this project has been provided by three local government bodies; Rockhampton City Council, Livingstone Shire Council and Fitzroy Shire Council as well as a grant from the Department of Environment and Heritage through the Recycling Grants Scheme. I wish to thank my research assistant Ms Donna Rayner for dedication to the project. REFERENCES Axtell, R.C. and J.J. Arends1990. Ecology and management of arthropod pests of poultry. Annual Rev Entomol 35: 101-26. Booth,C. and D.C. Sheppard 1984. Oviposition of the black soldier fly, Hermetia illucens (Diptera: Stratiomyidae): Eggs, masses, timing, and site characteristics. Environ Entomol 13: 421-23. Bradley, S.W. and D.C. Sheppard 1984. House fly oviposition inhibition by larvae of Hermetia illucens, the black soldier fly. J Chem Ecol 10: 853-859. Brues, C.T. 1928 Studies on the fauna of hot springs in the western United States and biology of thermophilous animals. Proc Amer Acad Arts Science 63: 139-228. Fatchurochim, S., C.J. Geden and R.C. Axtell 1989. Filth fly (Diptera) oviposition and larval development in poultry manure of various moisture levels. J Entomol Sci 24: 224-231. Sheppherd, D.C. 1983. House fly and lesser house fly control utilising the black soldier fly in manure management systems for caged laying hens. Environ Entomol 12: 1439-1442. ============== Jerome F. Rigot Department of Environmental Toxicology 4416 Meyer Hall University of California Davis, CA 95616 _____________ Work #: (916)752-5896 Fax #: (916)752-3394 Home #: (916)753-7617 E-mail: jfrigot@ucdavis.edu