Report from the Parma Cocoon Testing Lab

Karen Strickler and Crystal Booth

1994-1999

Comparisons between years

Machine Damage

Sex Ratio Tests

Comparing bee boards

Comparisons between years.

The Parma Cocoon Testing Lab has been testing bee cells for growers in the Northwest, particularly in Idaho, Oregon and Nevada, since the winter of 1994-1995. Approximately 40-50 growers use our services each year. Most of these growers have submitted samples two or more years. Most submit samples to see what their bee returns are in order to judge their needs for the next season.

Table 1 (below) gives mean, maximum and minimum % live cells, live cells per pound, and the most important morality factors for samples received before March 16, 2000. As expected, % live bees and live bees per pound are much lower for most growers in the USA than for Canadian growers. Chalkbrood is much higher. Pollen ball mortality tends to be higher in the USA than in Canada, as do parasitized cells. Parasitism reached a peak in 1997, but has been decreasing since.

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Machine Damage

This year for the first time we include values for machine damage in our report (Table 1). Percentages have been low for most growers in the past, so we did not bother to include them. However, some growers expressed concern about their machine damage rates this year. Indeed, average mortality due to machine damage increased from < 3.5% between 1994 and 1996, to >5% in the 1997-98 seasons. The average machine damage from the 1999 season is up to >7% so far. We do not know the reason, but would be happy to hear your suggestions.

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Sex Ratio Tests

We’ve been asked to do 5 or 6 sex ratio tests each year. These tests give an estimate of the percentage of live larvae that will actually emerge, and the proportion of females among the live bees. Out of a total of 25 samples between 1995 and 1998, we have seen an average of 93% (range 74-100%) of the live larvae successfully emerge in these tests. Of these, 46% on average were females (range 30-58%). This is very interesting, because published reports of sex ratio are about 35% females. Only 5 of our 25 samples have been lower than 40%. Perhaps pollen balls are more likely to occur in cells with male eggs and larvae. In addition, data reported in the proceedings of the 2000 Northwest Alfalfa Seed Grower's meeting show that the percentage of females increases with time during cold storage and incubation, probably because of male mortality during incubation. Males are smaller than females, and may deplete their energy reserves during incubation, making them less likely to emerge successfully. Regardless of the reason, our results suggest that you can expect a higher proportion of female cells from Northwest samples than the expected 35%. Keep this in mind when you calculate the number of gallons of bees from your fields. Females are desirable because they do most of the pollinating of alfalfa.

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Comparing cell quality in different kinds of bee boards

In 1999 we tested duplicate samples from a number of growers who compared bee boards from two different manufacturers. They put both types of boards in the same shelters, and punched out cells separately from each type of board. Thus, they can compare the quality of bees in different types of bee boards. Some of these samples have noticeable differences in parasite levels. This is one of the most effective ways of using the Parma Cocoon Testing Lab. We encourage growers to experiment with different types of bee boards, shelter locations, sanitation, etc. and see if you can find ways to improve the live bee count from your fields.