Found this online though not sure on availability... B. bassiana is available commercially as a microbial insecticide since Beauveria can now be mass produced by a fermentation process and formulated to enable the fungus to withstand ultraviolet light, and temperature and humidity extremes commonly encountered in the field. There are several products that contain B. bassiana, including Naturalis® and Mycotrol®; it is likely additional products will be registered with the EPA. Because it takes 3-7 days to kill an insect with B. bassiana, it will take some time to suppress the pest population when using these products. Thorough spray coverage is essential because fungal spores must contact the insect for infection to occur. Here is a link that might be useful: BT option

A bad infestation of whitefly can do serious damage to some plants. It takes a bit of persistence to get them under control, but it's certainly not impossible. I'd like to see you put the malathion away, as that chemical is highly toxic to you, your family, wildlife, and beneficial insects that might be present. I'd like to see you try some insecticidal soap. It is important that you direct the spray to the underside of the leaves, as this is where these insects hang out in all life stages. The soap product must make contact with the insects for it to work. (So does your malathion, which might be why it didn't do such a good job.) Also, Neem oil is quite effective against whitefly. It has a systemic effect, making it effective against sucking insects for a longer time. You should also try to direct the spray to the underside of the leaves for the best results. Neem acts as an anti-feedant and disrupts the normal life cycle of plant feeding insects. Lastly, horticultural oil can be helpful in controlling whitefly in all stages. Be sure to read the directions on the label for temperature warnings. Again, this product must be applied to the underside of the leaves. What are the plants that are giving you the most problem with whitefly? Some are very prone to infestation, while some plants are never bothered.

Proper greenhouse humidity is important both in preventing plant diseases and promoting healthy plant growth. High humidity can promote the Botrytis and other fungal diseases. High humidity also restricts plant transpiration, which in turn limits evaporative leaf cooling and can lead to overheating of plant foliage. If high humidity persists for a long time, the restriction of transpiration can limit the "transpiration stream" of nutrients and can lead to nutrient deficiencies. Low humidity is best avoided because it may increase foliar transpiration to the extent that the root system cannot keep up. Humidity is most accurately measured in terms of the "vapor pressure deficit" or VPD. This can be thought of as the drying power of the greenhouse air. However, most people measure humidity as relative humidity. Charts and programs are available to convert relative humidity to VPD. Humidity is perhaps the most difficult of the greenhouse conditions to control. Most growers simply aim to avoid the extremes of humidity. Over most temperature ranges, a GH humidity of 50-85% is generally safe. Low humidity can be managed with misters and foggers. It is also useful to shade plants under conditions of low humidity to reduce the rate of transpiration. Transpiring plants add water vapor to the greenhouse air, increasing the humidity inside the greenhouse. Therefore, managing high humidity starts with ventilation...replacing warmer, humid greenhouse air with cooler, drier outside air. Ventilation also involves significant energy losses, and therefore ventilation often must be accompanied by heating. Therefore, lowering greenhouse humidity with a combination of ventilation and heating can cost a lot of energy. Information provided by: Stressbaby

FWIW: probably not an immediate solution to your problem, but this works quite well for me. "the basic premise of my pest control program is: "everybody"s somebody"s lunch. I've got a variety of native plants throughout the yard (attracts birds) and I don't spray (allows beneficial insects to thrive). The ladybugs, lizards, birds and spiders have been reliable pest control, even during the whitefly infestation of a few years ago. I did have a mess develop on the bottom side of the banana leaves, which I sprayed twice with diluted insecticidal soap. Best luck.