Project Code: CE0311
Funded By Department for Environment, Food and Rural Affairs
Lead Research Centre
Central Science Laboratory,
Abstract of Research Proposal
The main objective of the proposed work is to investigate the behaviour, biology and the physiology of mite pests in stored cereals and oilseeds to improve detection and monitoring and inform the development of options for improved control. This will be achieved by measuring the effect of temperature, humidity and aeration on mite development and movement, by improving the ability to detect mites by trapping in premises and grain bulks, by quantifying trap effectiveness such that trap catches can be properly interpreted, and by reviewing knowledge on storage mite physiology to reveal potential novel methods of control. The work will bring two major advances to improved control of storage mite pests; it will allow mite pest potential to be quantified and thereby evaluated at it will guide research to discover alternative control strategies which do not depend on the use of conventional toxicants which have limited life. The results will be used to contribute to the integrated management practice for improving UK grain quality. The work is relevant to policy because it addresses the need to raise grain quality be reducing pest presence while minimising use of pesticides.
Summary of Objectives
To investigate the biology, behaviour and physiology of mite pests in stored cereals and oilseeds to improve detection and monitoring and inform the development of options for improved control.
1) To determine factors in the basic biology of storage mites which influence their development and detection by studying the combined effects of temperature, humidity and aeration on one representative species of each of the three principal genera found in stored grain.
2) To ensure that all three principal storage mite genera in storage premises can be detected by trapping and that the trap catches can be properly interpreted by measuring the effectiveness of the BT mite trap in catching G. destructor and T. putrescentiae.
3) To devise an effective bulk trap for storage mites of cereals and oilseeds based on “pitfall cone” principles already established for detecting grain insects.
4) To review existing knowledge on storage mite physiology to plan and undertake preliminary investigation of the most promising novel approaches for mite suppression and control.
Summary of progress from 98/99 annual report:
The main purpose of this project is to address the increasing problem of mites in stored grain by establishing essential information upon which their detection and control depend. Work so far has focused on factors which influence mite development and movement in grain.
In each case, laboratory experiments have been undertaken to establish the combined effects of temperature, humidity and aeration on three mite species which are representative of the principal mite genera found in stored grain. These species are Acarus siro, Lepidoglyphus destructor (Schrank) and Typophagus longior (Gervais). The grain used was English milling wheat of the Mercia variety, certified free from pesticides and mites. Experiments were run under four combinations of temperature and humidity. Chosen temperatures were 20oC and 10oC, representative of those when grain goes into store and which are achievable subsequently. Chosen relative humidities were 80% and 70% representative of the day and night average in the UK and a threshold for mite survival respectively. These humidities were approximated by running the experiments in controlled environment rooms and by adjustment of the starting moisture content of the grain.
In the experiments on mite development, for each mite species, ten virgin adult female and male pairs were placed in each of 20 specimen tubes with 15g of wheat in a 0.4m3 polystyrene box full of wheat. One box for each species was then placed at each of the four sets of temperature and relative humidity conditions for 35 days. Ten of the specimen tubes in each box were aerated at an equivalent rate of 10cu m/h/t, this being typical of a rate for cooling. Numbers of eggs, larvae, nymphs and adults in each tube at the end of the experiment were counted using a modified flotation test.
Temperatures, monitored continuously inside the boxes, remained within 1.5oC of intended throughout the experiments. Moisture contents, measured at the start and end of the experiments, were within 0.2% of intended at the start, with maximum differences of +0.8% and -1.4% at the end.
Over the course of the experiment, for A. siro there was a smaller increase in total mite numbers from the initial 20 at the lower temperature (to about 120 mites at 10oC compared with to about 450 mites at 20oC). The effect of humidity was less pronounced (for example at 20oC about 440 mites at 70% rh compared with about 480 mites at 80%). At all four conditions, the increase in total number of A. siro was significantly greater (5% level) when aerated. With L. destructor the greater increase in numbers at the higher temperature was seen only at the higher humidity. At each temperature, there was a greater increase at the higher humidity (to about 96 mites at 80% rh compared with to about 65 mites at 70% both at 10oC). Aeration resulted in a significantly smaller increase in total mite numbers but only at 20oC. With T. longior the increase in total number of mites was greater at the higher temperature for both humidities and at the higher humidity for both temperatures. Aeration resulted in significantly smaller increase in mite numbers but only 20oC. With T. longior the increase in total number of mites was greater at the higher temperature for both humidities and at the higher humidity for both temperatures. Aeration resulted in significantly smaller increases in mite numbers except at 10oC and 80%rh.
These experiments have shown that temperature, humidity and aeration can all affect the increase in mite numbers over durations which are relatively short compared with typical storage periods. The relative importance of these effects, and in some cases the direction in which the effect occurs, probably depend on a combination of factors including proximity to optimum developmental conditions, whether the species is an external or internal feeder on the grain, the occurrence of fluctuations in populations and the limitations forced on this work by practical exigency, for example confirming mites within the experimental tubes. These factors will be clarified in the next stage of the work, which will apply the expertise obtained so far, to a grain bulk.
The experiments examining the effect of airflow on mite movement were conducted in 8 cylinders, 1m high by 0.3m diameter containing 50kg of wheat. Each cylinder was charged near the base with roughly 15,500 A. siro, 21,250 T. longior and 5,200 L. destructor, all adults. At each set of conditions, four of the cylinders were attached to vacuum lines to give an airflow of 8.3 litres/minute. The other four cylinders were not aerated and used as controls. After 168 hr a sample spear was used to remove grain at five different positions and at eight depths (on the surface, then at intervals of 13cm depth) for each sample point. Samples were analysed using a modified flotation technique.
In all cases mites dispersed from the release point at 91cm depth. At 10oC, 80%rh only a minority of mites had moved into the upper half of the cylinders (range 20 to 32%). At 10oC, 80% r.h. a larger proportion of the mites of all three species were found in the top half of the cylinders (range 44 to 55%), the majority of these being found at the surface (16 to 25% of the starting number). However, in neither case was there any evidence to suggest that the airflow had any effect. At 20oC, 80% r.h., the air flow appeared to have an effect: the proportion of mites found in the upper half of the cylinder ranged between 43 and 50% with aeration but between 26 and 33% without. At these conditions, the proportion found on the surface ranged from 16 to 19% with aeration but from 3 to 5% without. it would seem that at the lower temperate and lower humidity, movement was relatively small. Raising the humidity alone allowed more movement but it was only when the temperature was raised too that the airflow appeared to affect mite movement, by increasing numbers moving upwards.
Start date: 01/04/98
Completion date: 31/03/02