Organophosphate and carbamate insecticides have been used to treat citrus pest problems for more than 40 years. From 1990 to 1998, we documented California red scale and yellow scale resistance to these insecticides. Armored scale resistance is found on an estimated 40% of 163,000 acres of citrus in the San Joaquin Valley. Citrus growers have responded by either increasing their use of natural enemies, especially the parasitoid wasp Aphytis melinus, or by applying newly registered insect growth regulator or neonicotinoid insecticides. While the California red scale problem is, for the moment, greatly reduced, outbreaks of cottony cushion scale are occurring because the new insecticides are highly toxic to the predatory vedalia beetle.

To protect uninfested areas of California from glassy-winged sharpshooter (GWSS), the disinfestation of citrus nursery stock prior to shipment is essential. A nonnative insect, GWSS transmits the bacterium that causes Pierce’s disease in grapevines. In our study, GWSS adults were especially sensitive to two categories of insecticides, the pyrethroids and systemically applied neonicotinoids. Several insecticides, including the carbamate carbaryl and a few of the foliar neonicotinoids were highly effective in preventing GWSS nymphs from successfully emerging from egg masses. While no pesticide treatment will perfectly protect nursery citrus, a treatment plan that includes a combination of insecticides that are effective against adults and emerging nymphs will minimize the chance of transporting GWSS throughout California.

The insect and mite control potential of natural and biological toxins has been recognized for several centuries. Bacteria, viruses, protozoa and fungi are the primary groups of microorganisms known to reduce insect populations; they often occur naturally in fields and function as components of biological control. Beneficial nematodes are also being used for pest control, especially against soil insects. The isolation of toxic metabolic compounds from microorganisms continues to be a fruitful research area, although there are barriers to their successful marketing and distribution. Another, more controversial way to deliver these insect-specific toxins to the target pest is through genetically modified plants, such as those modified to express Bacillus thuringiensis (Bt) toxins. Oils and particle films also have important niche uses for pest control.

A number of novel insecticides have recently been registered for insect control in agriculture. A major advantage of these new products is that they act on insect biological processes that humans do not experience, such as molting. Many also have greater selectivity to target specific species, so they are less likely to harm natural enemies when compared with the broader spectrum organophosphate, carbamate, neonicotinoid and pyrethroid insecticides. Such novel insecticides currently in use include four targeting lepidopteran pests, three targeting sucking insects, one specific to dipteran leafminers and one insect growth regulator that controls a wide range of insects. One negative aspect of these insecticides is that because of their narrower range of activity — controlling only a limited number of pests — growers may need to apply additional pesticides for secondary pest groups that have poor biological control, increasing the total number of treatments per acre and total pest-control costs.