6.3. Reduction in egg production

Although often neglected, plant foodstuffs harvested by workers can harm colonies and potentially impact queen physiology. When the nectar and pollen of Aesculus californica (California buckeye) is intensively harvested, returned to the hive and consumed, queens lay only male eggs and can be superseded. The poisoning stops generally at the end of buckeye bloom (Vansell, 1926). A deleterious compound of the nectar was suspected but not isolated.

Johansen (1977) mentioned that queens may be affected by insecticides and behave abnormally. For instance, they may produce a an abnormal brood pattern. This was the case with ovicidal effects of certain herbicides. When package bees containing a laying queen were fed with the 2, 4, 5 T and 2, 4 D herbicides at 100 mg/kg, some of the eggs were unable to hatch, thus presenting as a bad brood pattern (Morton and Moffett, 1972).

Bendahou et al. (1999) suggested a reduction in the amount of vitellogenin in eggs (see: Tufail and Takeda, 2008)explained a low hatch rate of eggs, and , consequently, the resulting high frequency of supersedure observed in colonies fed weekly with sugar syrup including 12.5 µg/l of cypermethrin, a pyrethroid insecticide.

Dai et al. (2010) validated that the hatch rate of eggs can be reduced when queens are fed sublethal doses of bifenthrin and deltamethrin, both pyrethroid insecticides. Moreover, the daily number of laid egg was reduced 30 to 50% for bifenthrin and deltamethrin, respectively.

Ovicidal effects, suggested by egg replacement in the cells, can occur after exposure to IGR insecticides such as fenoxycarb or diflubenzuron (Thompson et al., 2005). The maximum replacement rate measured in the first week after treatment was 60 % and 90% for fenoxycarb- and diflubenzuron-treated colonies respectively. No queens successfully mated and laid eggs when treated with fenoxycarb.

Other IGR insecticides acting on the Juvenile Hormone III titre in the haemolymph, were shown to inhibit vitellogenin synthesis (Pinto et al., 2000).

The questions of side-effects of acaricide treatments on queen egg laying success were investigated for fluvalinate and coumaphos. After treating queens and attendant bees placed in Benton mailing cage with specially designed strips of fluvalinate for three days, Pettis et al. (1991) observed no differences in colony acceptance of queens, brood viability or supersedure rates. After moderate queen larvae exposure to fluvalinate in a starter/finisher colony, Haarmann et al. (2002) confirmed the statistical absence of differences compared with the control group of newly mated queens, with queen weight, ovary weight and the number of sperm.

Coumaphos, another acaricide/insecticide, was shown to be more toxic than fluvalinate by Haarmann et al. (2002). They contaminated frames of grafted cells placed in starter colonies for 24 h, with two plastic strips each containing 1.360 g of coumaphos. Afterwards, queen cells were raised in finisher colonies. At the end of the experiment, queen cells contained 8 to 28 mg/kg coumaphos depending on the presence or absence of contact of the strips with the grafted cell frames. In coumaphos treated groups, the queen and ovary weights were significantly lower. After artificial contamination of the wax of queen cups with 100 mg/kg of coumaphos, Pettis et al. (2004) showed a negative effect on young queen acceptance and on their weights.