Sara J. Scott

Effects of Spirotetramat on Aonidiella aurantii (Homoptera: Diaspididae) and Its Parasitoid, Aphytis melinus (Hymenoptera: Aphelinidae)

ABSTRACT Laboratory and field studies were conducted to measure the effects of spirotetramat on life stages of California red scale, Aonidiella aurantii (Maskell), and a primary parasitoid, Aphytis melinus DeBach. Organophosphate-resistant and -susceptible populations responded similarly to spirotetramat, suggesting there is no cross-resistance between these insecticide classes. First and second instar male and female A. aurantii were 10- and 32-fold more susceptible to spirotetramat (LC50 = 0.1–0.2 ppm) compared with early third (LC50 = 1.5 ppm) and late third instar females (LC50 = 5.3 ppm). The LC99 value indicated that late stage third instar females would not be fully controlled by a field rate of spirotetramat; however, spirotetramat would reduce their fecundity by 89%. Field applications of spirotetramat in two water volumes and using two adjuvants (oil and a nonionic spray adjuvant) showed similar reduction in A. aurantii numbers, even though the higher water volume demonstrated more complete coverage. These data suggest that this foliarly applied systemic insecticide can be applied in as little as 2,340 liters/ha of water volume, minimizing application costs, and that the two adjuvants acted similarly. The endoparasitoid, A. melinus, was unaffected by the field rate of spirotetramat when it was applied to the host when the parasitoid was in the egg or larval stage. Adult A. melinus showed 2 wk of moderate reductions in survival when exposed to leaves with field-weathered residues. Spirotetramat is an integrated pest management compatible insecticide, effective in reducing A. aurantii stages and allowing survival of its primary parasitoid A. melinus.

Chlorpyrifos Bioassay and Resistance Monitoring of San Joaquin Valley California Citricola Scale Populations

ABSTRACT The responses to chlorpyrifos of six populations of citricola scale, Coccus pseudomagnoliarum (Kuwana) (Hemiptera: Coccidae), were tested using a leaf dip bioassay, and two- to nine-fold resistances were found. LC50 responses of nymphs ranged from 7.5 to 68.9 ppm and LC90 responses ranged from 20 to 222 ppm chlorpyrifos. A population tested monthly during August-October showed up to 3.5-fold differences in LC50 responses but no differences in LC90 responses as scale size increased. A diagnostic concentration of 178 ppm chlorpyrifos was used to test 93 populations from throughout the San Joaquin Valley California during 2006–2009 by using a leaf dip bioassay. Of the populations tested, 41% showed >20% survival after exposure to the diagnostic concentration of chlorpyrifos, indicating resistance problems. Research is needed to relate the level of survival of the scales in the bioassay to the field efficacy of the insecticide. Tulare County citrus growers applied a higher number of organophosphate and carbamate insecticides during the 15-yr period from 1994 to 2008, and these orchards showed a higher average scale survival of chlorpyrifos and a higher number of locations with resistant scale compared with the other San Joaquin Valley counties. Chlorpyrifos resistance is a significant issue for citricola scale management because biological control is ineffective in the San Joaquin Valley and the alternative neonicotinoid and insect growth regulator (IGR) insecticides require more frequent application.