Hi all
I mentioned two factors which could cause lack of sperm viability and possibly drone laying queens. 1) miticides and 2) environmental factors. Here is evidence that pesticides could be at work in this problem:

Queen survival and productivity are intimately connected to proper mating as the depletion of sperm results in costly replacement of the queen by the colony, which can only successfully occur during specific periods of the year. Recent data linking poor queen health to colony mortality, possibly because of low quality stored sperm from stressors such as miticides or insect growth regulator insecticides, highlight the urgent need for investigating possible factors that may affect male reproductive success among non-target, beneficial insects.

Even though neonicotinoids did not appear to influence the quantity of total sperm produced by males, we did observe a significant negative effect on sperm viability, which in turn resulted in a significant reduction in the number of living sperm produced by neonicotinoid drones. Although only a small proportion of transferred sperm is stored by the queen, any decrease in sperm quality could have negative consequences.

For the first time, we have demonstrated that frequently employed neonicotinoid insecticides in agro-ecosystems can elicit important lethal (reduced longevity) and sublethal (reduced sperm viability and living sperm quantity) effects on non-target, beneficial male insects; this may have broad population-level implications ... 

By demonstrating the effects of neonicotinoid insecticides on male insect reproduction, our study provides a possible mechanism, in addition to introduced parasites and other land-use practices, for honeybee queen failure ... 

Although recent improvements to regulatory requirements for evaluating the environmental impacts of insecticides have been adopted, none so far directly address the reproduction of beneficial insects.

Straub, Lars, et al. "Neonicotinoid insecticides can serve as inadvertent insect contraceptives." Proc. R. Soc. B. Vol. 283. No. 1835. The Royal Society, 2016.

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