The potential management of citrus leafminer, Phyllocnistis citrella (Stainton) (Lepidoptera: Gracillariidae), by use of soluble silicon fertilizers

The citrus leafminer (CLM), Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae) is an invasive herbivorous insect. CLM damage results in decreased sales of horticultural production for garden centers and homeowners. Nursery citrus growers in California treat for CLM several times per season primarily with the insecticide imidacloprid. The limitations and high cost of chemical control, in addition to toxicological problems such as insecticide persistence and resistance, justify the adoption of alternative management tactics. One non-chemical option for insect pest management is entomopathogenic nematodes (EPNs). Recent studies have shown greater EPN efficacy when applied with BarricadeRTM gel, a fire retardant gel. BarricadeRTM temporarily maintains moisture on the leaf surface, facilitating nematode survival. We sought to determine if UV protectants added to the BarricadeRTM gel increase the efficacy of EPNs, to quantify the retention and survival of EPNs applied with gel, and to assess whether the gel facilitated nematode movement on an exposed surface The addition of UV protectants to the gel enhanced the protective properties of the formulation. Furthermore, we conclude that low concentration gel solution extends IJ survival up to 8 hours. Bottom-up methods of insect population management focus on modifying the host plant, often by strengthening plant defenses through nutrient management. Preliminary studies by our lab found a reduction in CLM feeding damage following treatment with soluble silicon. To expand on these results we sought to determine CLM oviposition preference, host acceptance, and preference for host volatiles. CLM adults were given a choice between a soluble silicon treated plant and a control. Adults were allowed to oviposit, then citrus leaves were inspected for eggs. CLM adults were also offered a dual choice in a glass Y-tube olfactometer. CLM adult females laid significantly fewer eggs on plants treated with soluble silicon. The evidence strongly suggests a silicate-induced change in the tactile or chemical profile of the leaf occurred. We also aimed to examine whether soluble silicate fertilizer could affect CLM population growth. To that end we sought to determine CLM larval feeding performance, quantify differences in rate of development and mortality of the larvae and pupae. The development of CLM from larvae to adult was observed and compared on soluble silicon fertilized plants vs. controls. We calculated net replacement rate (R0) of CLM. CLM on soluble silicon fertilized plants had significantly lower survivorship than CLM on controls. The lower survivorship of CLM on soluble silicon plants suggests the possibility of induced plant defensive chemicals in the plants. The lower R0 of the treated group is a strong indication that CLM population growth is reduced under the fertilizer regime. Our results show that the enhanced survival and mobility provided by the anti-desiccant and anti-UV materials have the potential to make EPNs more efficient at targeting foliar pests. Thorough testing of the combined results of soluble silicon and EPNs on CLM populations will determine the utility of these techniques in integrated pest management programs for CLM.