Does Sand Control Chalcid Parasites?

Table 1:  initial % live

Table 2: % actual  emergence

Does sand + pyrethrin work better?

Table 3: emergence from sand + pyrethrin

Conclusion

This experiment was conducted at Ron Bitner's suggestion after he read a report from Russia about sand as a method to control chalcid parasites of leafcutting bees.

Materials and Methods

In May, 1997, four gallons of alfalfa leafcutting bee cells containing parasitized cells were divided between five trays, three quarts of cells in each. One tray was left untreated as a control. Cells in two trays were covered with commercial sand used for potting mix. Cells in the remaining two trays were covered with vermiculite. X-ray analysis gave initial estimates of live larvae and parasites. The trays were incubated at 86° F and 50% relative humidity until adult bees no longer emerged from cells, at which point the temperature of the incubator was decreased to 41° F to prevent further parasite emergence. A ¼ cup sample from each of the trays was examined for the proportion of cells showing signs of bee emergence or parasites, or containing dead pupae or dead bees. Cells containing chalkbrood, pollen balls or dead larvae were ignored in this analysis, since they were dead before the experiment started.

Materials and Methods

Table 1:  initial % live

Table 2: actual % emergence

Does sand + pyrethrin work better?

Table 3: emergence from sand + pyrethrin

Does sand + pyrethrin work better?

We wondered whether a mixture of sand and pyrethrin might do a better job of controlling parasites. To test this, bee cells were incubated at 90° F, 60% relative humidity starting on May 22, 1997. Six days later, 200ml volumes of cells were placed in each of 26 one-pint plastic containers. Just before expected parasite emergence, 150 ml of sand treated with varying concentrations of pyrethrin were added to cover the bee cells. X-ray analysis indicated that the sample contained approximately 5% parasites, and bees had developed into black pupae. Containers were left open until bees started to emerge, to allow parasites to move between containers. When bees began to emerge (June 9), lids were placed on containers to monitor the location of emergence. The number of emerged bees was counted daily for each container until no further emergence took place. At this time (June 23), the incubator temperature was reduced to 41° F to inhibit further development of parasites. The number of cells containing dead bees, dead pupae, and parasites was recorded for each container.

Parasitism rates for the treated sand were about half the rate for untreated cells, and parasitism for dry sand without pyrethrins was only 5% (Table 3). However, there was substantial mortality of bees in cells that did not emerge, again probably due to unsuccessful parasitism. The dry sand treatment also had a high mortality of bees that died after emergence. We suspect that the dry sand was abrasive, and may have caused the bees to bleed to death as they crawled through the sand. The pyrethrin had no effect.

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