Banks Grass Mite (Acari: Tetranychidae) Suppression May Add to the Benefit of Drought-Tolerant Corn Hybrids Exposed to Water Stress

Spider mite (Acari: Tetranychidae) outbreaks are common on corn grown in the arid West. Hot and dry conditions reduce mite development time, increase fecundity, and accelerate egg hatch. Climate change is predicted to increase drought incidents and produce more intense temperature patterns. Together, these environmental shifts may cause more frequent and severe spider mite infestations. Spider mite management is difficult as many commercially available acaricides are ineffective due to the development of resistance traits in field mite populations. Therefore, alternative approaches to suppress outbreaks are critically needed. Drought-tolerant plant hybrids alleviate the challenges of growing crops in water-limited environments; yet, it is unclear if drought-tolerant hybrids exposed to water stress affect mite outbreaks under these conditions. We conducted a greenhouse experiment to evaluate the effect of drought-tolerant corn hybrids on Banks grass mite [Oligonychus pratensis Banks (Acari: Tetranychidae)], a primary pest of corn, under optimal irrigation and water-stress irrigation. This was followed by a 2-yr field study investigating the effect of drought-tolerant corn hybrids exposed to the same irrigation treatments on Banks grass mite artificially infested on hybrids and resident spider mite populations. Results showed that water-stressed drought-tolerant hybrids had significantly lower Banks grass mite and resident spider mite populations than water-stressed drought-susceptible hybrids. Interestingly, water-stressed drought-tolerant hybrids had equal Banks grass mite populations to drought-susceptible and drought-tolerant hybrids under optimal irrigation. We posit that planting drought-tolerant hybrids may suppress spider mite outbreaks in water-challenged areas.

Acarine Pests

This chapter examines mites. Mites are arthropods in the class Arachnida, order Acari, and have several morphological and physiological characteristics that differ from insects. Many mites of economic importance in agriculture develop very rapidly and complete several generations each year. Mouthparts of mites are described as rasping and sucking — the mite rasps a wound on the surface of plant tissue and then laps or sucks up the resulting plant exudate. Several mites attack turfgrass in various regions of North America. The chapter then looks at the bermudagrass mite, the zoysiagrass mite, the buffalograss mite, the winter grain mite, the clover mite, and the banks grass mite.

A life table analysis to evaluate biological control of banks grass mite using the predatory mite, Galendromus flumenis (Acari: Phytoseiidae)

The predatory mite, Galendromus flumenis (Chant) (Acari: Phytoseiidae), has shown promising traits for biological control of Banks grass mite, the major pest of date palms in California. In the present study, reproduction and population growth parameters of G. flumenis on Banks grass mite eggs were studied at 34ºC, 50±10% RH and a photoperiod of 16: 8 (L: D) hours. 100 percent of eggs hatched and 63.5 percent of the emerged larvae survived to adulthood. The total immature developmental time was 5.7 and 5.5 days for females and males, respectively. The sex ratio of G. flumenis was 0.70 (females/ females+ males). Mated females laid on average 1.6 eggs per day and 19.9 eggs during their mean ovipositional period of 12.5 days. The net reproductive rate (R0) was 11.5 females/ female/ generation, the intrinsic rate of increase (rm) was 0.200 females/ female/ day, the finite rate of increase (λ) was 1.222 population multiplication/ day, the mean generation time (T) was 12.2 days, and the doubling time (DT) was 3.5 days. The lower rm value of G. flumenis than that of its prey (0.24–0.48) explains why Banks grass mite escapes control by G. flumenis in field. These results suggest that augmentative release of this predator would offset the lower rm of the predator, thereby contributing to the control of Banks grass mite. Combined with the benefit of early releases determined in companion studies, future field studies with G. flumenis are being planned.