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The relative toxicity of pesticides to adult predaceous phytoseiid mites in relation to plant feeding mites was evaluated by the slide dip technique. The toxicity ratios of Typhlodromus occidentalis Nesbitt, Amblyseius hibisci (Chant), A. stipulatus Athias-Henriot, Iphiseius degenerans (Berlese), and Phytoseiulus persimilis Athias-Henriot were compared to Panonychus citri (McGregor) or Tetranychus pacificus McGregor. T. occidentalis was more resistant to many of the pesticides than the plant feeding mites; the other 4 species of predators were generally more susceptible to the pesticides than P. citri or T. pacificus . Azinphosmethyl and Vendex® (hexakis (beta, beta-dimethylphenethyl)-distannoxane) had similar order of toxicity to the 4 predaceous species as the plant feeding mites, and tricyclohexylhydroxytin was less toxic to all 5 predaceous mites than to P. citri or T. pacificus . A. hibisci eggs were exposed to concentrations of citrus pesticides by utilizing the Potter Tower sprayer. A wide range of susceptibility of both eggs and immatures was shown to exist to the various pesticides evaluated. The egg stage was relatively tolerant to a number of the pesticides evaluated. Propargite and Vendex residues were the least toxic to the immature mites.

Response of the Pacific spider mite, Tetranychus pacificus McGregor, and the citrus red mite, Panonychus citri (McGregor), to laboratory and/or field applications of thioquinox, Morestan® (6-methyl-2,3-quinoxalinedithiol cyclic S,S .dithiocarbonate), and related compounds was evaluated, Morestan was most toxic to the nymphs of P. citri and least toxic to the eggs. Twenty-five laboratory selections with Morestan failed to bring about a change in the susceptibility of T. pacificus to this compound. Residues of Morestan and some related compounds caused a high percentage of adult P. citri to abandon the treated fruit surface. About 50% of these migrating mites died even though they immediately reached untreated lemon leaves. High humidities decreased the migrating response and mortality of P. citri to Morestan residues. Thioquinox and Morestan field applications resulted in as adequate control or more effective control of P. citri as petroleum oil or other acaricide applications. Morestan residues resulting from field applications influenced the adult mite migrating activity or affected mortality for 50-90 days after treatment. Residues above 3.5 ppm on oranges or 2.0 ppm on lemons did not increase percent mite mortality or result in increased migration; as the amount of residue decreased below 3.5 or 2.0 ppm, respectively, the percent mortality and loss by migration decreased in linear proportion to the amount of residue.

A strain of the Pacific spider mite, Tetranychus pacificus McGregor, which had developed resistance in the field to demeton treatments was subjected in the laboratory to parathion selection pressure at the 70% mortality level through 10 selections without further change in the degree of cross resistance to parathion. Starting with a susceptible strain, six to nine such selections with parathion and ethion resulted in high degrees of resistance to both accuracies. Similar selection procedures using Aramite® (2-( p-tert -butylphenoxy) isopropyl 2-chloroethyl sulfite) resulted in a 10-fold increase in resistance after 15 selections; but using Chlorobenzilate® (ethyl 4,4′-dichlorobenzilate or Kelthane® (1, 1-bis( p -chlorophenyl)-2,2,2-trichloroethanol) resulted in no change in susceptibility after 23 or 22 selections, respectively. In cross resistance evaluations parathion- and ethion-resistant strains were cross resistant to the other organ phosphorus accuracies evaluated but not to the specific acaricides. Aramite-, Chlorobenzilate-, and Kelthane-selected strains were cross resistant to some organophosphorus compounds but not to other specific acaricides. This response is contrasted with the response of house flies ( Musca domestica L.) to selection pressure with insecticides.

Tricyclohexyl tin hydroxide (TCTH) was found to be relatively toxic to the citrus red mite, Panonychus citri (McGregor), and the Pacific spider mite, Tetranychus pacificus McGregor. It was slightly more toxic to the nymphs than to the adult females and more toxic by direct contact than as a spray residue. There was no change in the susceptibility of our laboratory strain of the Pacific spider mite after 10 selections with TCTH where selection occurred at the LC50 level. Residues from field-spray applications to lemons were toxic to adult mites for 30–60 days after applications. The time interval of toxicity was dependent on the dosage and time of year applied. During an elapsed period of more than 20 days a sizeable proportion of TCTH residues could be removed from lemon fruit and leaves by a detergent wash as indicated by the toxicity of the residues to adult female mites. Effective control of the citrus red mite was achieved in more than 20 experimental orchards by dilute or “misttype” spray applications. However, under some conditions TCTH sprays were slightly less effective than the quinoxiline applications which were used as a standard treatment. Necrotic spots were observed on very young citrus growth following some spray applications. Severe leaf drop occurred when TCTH was applied to lemon trees immediately following an application of 1.2% petroleum oil.

Under field conditions citrus red mite ( Panonychus citri (Mc-Gregor)) populations became resistant to demeton and Tedion® (2,4,4′,5-tetrachlorodiphenyl sulfone) following 3 to 5 applications, to Kelthane®(4,4′-dichloro- alpha -(trichloromethyl)benzhydrol) after 7 to 12 treatments, to Neotran® (bis( p -chlorophenoxy) methane) as a result of 14 sprays but remained susceptible to Aramite® (2-( p-tert -butylphenoxy)-1-methylethyl 2-chloroethyl sulfite) through 19 treatments covering a period of 8 years. Alternating acaricides, combining acaricides into a single treatment, or combining acaricides with petroleum oil did not increase the possible number of applications before resistance developed. Where demeton was ineffective and mites had developed resistance to organophosphorus compounds in general, ethion applications resulted in adequate control even though laboratory tests indicated a 10-fold degree of resistance to ethion. Resistance to ovex continued for the 8 years covered by this study; but Neotran-resistant mites became susceptible again in 3 years where Neotrun treatments had been replaced by a Tedion and petroleum oil combination.

Cycloheximide and its acetate, acetoacetate, oxime, semicarbazone, and thiosemicarbazone derivatives were evaluated in the laboratory to ascertain their toxicity to and effects on the fecundity of the citrus red mite, Panonychus citri (McGregor), on citrus, and the Pacific mite, Tetranychus pacificus McGregor, on bean seedlings. Laboratory sprays of these compounds, in the order listed, produced injury to green lemon fruit at concentrations of 2, 0.5, 100, 40, 5, 10 ppm, respectively, and to bean seedlings at 100, 25, 1000, 100, 100, and 100 ppm, respectively. None of the compounds were highly effective in producing direct mortality to either mite species at concentrations which were nonphytotoxic. At concentrations of 10 ppm or above, spray applications of each compound, except the thiosemicarbazone, materially reduced the fecundity of both mite species. In field evaluation trials, the oxime was the only one of these compounds that showed promise for control of P. citri . Most effective control resulted when applications were made between the cycles of plant growth. When applications were made during the growth cycle, adult female mites moved onto new growth where egg laying returned to normal.

The comparative toxicity of a p -chlorophenyl, some 2,4-dichlorophenyl and about 55 homologous 2,4,5-trichlorophenyl phosphoramidothioates and phosphoramidates to susceptible and acaricide-resistant strains of Tetranychus pacificus McGregor and Panonychus citri (McGregor) were investigated. The 2,4,5-trichlorophenyl was the only series sufficiently toxic to the resistant strains to be of interest. Of the alkoxy homologues of this series, the isopropyl substitutions resulted in the most toxic compounds to both the susceptible and resistant strains of both mite species, and the propyl and butyl substitutions resulted in the least toxic compounds of the series. Compounds resulting from the alkylamido substitutions to the phosphoramidothioates decreased in toxicity to T. pacificus as the length of the substitution chain increased. The chain length of the alkylamido homologues did not decrease the toxicity of the resulting phosphoramidatc compounds to either mite. The phosphoramidates were as toxic and frequently more toxic than their phosphoramidothioate analogue.

Studies of populations of the citrus bud mite, Aceria sheldoni (Ewing). over a period of 2 to 5 years in treated and untreated plots in four southern California lemon orchards are reported. In untreated plots a rapid increase in infestations in lemon buds started in Mayor June and peaked in August or September. In some years high populations were maintained throughout the fall and winter; in other years populations gradually decreased during the winter. In either case, populations fell to an annual low during April and May. These general population trends were correlated with seasonal climatic changes and plant growth cycles. Warm summer weather favorable for plant growth and also for mite dispersal resulted in rapid increase in infestation, whereas winter conditions appeared to reduce movement from one bud to another. Periods of low humidity during the winter or spring appeared to be major factors in the decline of infestation within the buds during this period. An unusually hot period in September 1955 resulted in a sharp decrease of infestation, especially in the orchard farthest from the coast. The summer population increase was about 1 month later under fruit buttons than in the buds. Populations under fruit buttons were higher than bud populations during most of the year. Applications of petroleum oil and of Aramite in both fall and spring were necessary for adequate control. Chlorobenzilate was most effective when applied between the first of June and the last of September, and a single application during this period kept mite populations low for a year.

Trends of citrus red mite, Panonychus citri (McG.), populations on untreated trees, as well as the intervals during which potentially injurious populations were present on trees exposed to a variety of treatment schedules, were studied. Seasonal citrus red mite population cycles occurred in the orchards in each of the 5 years. The specific time of each year in which these populations were increasing or decreasing varied from year to year depending on the seasonal growth cycles of the tree and the direct effects of weather extremes (hot. dry periods) on the miles. Application schedules ine1nding two or three treatments were Suggested. The number and timing of the applications were dependent on whether mite populations started to increase in late summer or rail following the annual early summer decline.

Laboratory and field-laboratory methods are described for measuring the rate that residues from spray applications of acaricides become unavailable or nontoxic to the citrus red mite, Panonychus citri (McGregor). The relative duration of effective persistence found by use of these methods was correlated with the field control of this mile achieved from spray applications in 3–5 orchards. A closer correlation was noted between duration of effective persistence and the control by field application than between degree of toxicity and field control. It was concluded that persistence evaluations are a valuable addition to laboratory toxicity studies in selecting potential acaricides, but the combined toxicity and persistence evaluations do not always serve as reliable indicators of acarotidal effectiveness.

The acaricidal activities of carbamoyloxy phosphorodithioate compounds having the following general structure were valuated on susceptible (S) and organophosphorusresistant (R) strains of the Pacific spider mite, Tetranychus pacificus McGregor, and the citrus red mite, Panonychus citri (McGregor): ![Formula][1] Compounds where X = C2H4 were toxic, though minimally, to the S strains but nontoxic to the R strains. The additional incorporation of a CH2S group (X = CH2SC2H2) resulted in compounds which were toxic to both S and R strains of these mite species. The effects of both P-and N-substitutions on acaricidal activity were evaluated and the results are briefly discussed. None of the 34 compounds evaluated were as toxic to the R strains as to the S strains, indicating the existence of cross resistance to carbomoyloxy phosphorodithioates in organophosphorusresistant mite strains. [1]: /embed/graphic-1.gif

The citrus bud mite, Aceria sheldoni (Ewing), is one of the most serious pests of lemons in the coastal areas of California. In 1941, Boyce & Korsmeier found that petroleum oil sprays were effective in control of this mite pest, and since that time these sprays have been largely relied on for control. In citrus culture, however, there are many situations in which it is inadvisable to apply petroleum oil sprays. Therefore, studies directed toward findng a substitute chemical control have been in progress at this station for several years.

Several acaricides were tested for efficacy against citrus rust mite in a lemon grove between Oceanside and Vista, California. Treatments were applied on Aug 13 by handgun (450 psi) with about 1200 gal per acre. There were four single-tree replicates per treatment. Mites were counted with a 14X hand lens or 12X hand lens with grid; four subsamples of 1 cm2 each were counted on each fruit, and 10 fruit were counted on each tree.

Several acaricides were tested for efficacy against citrus bud mite in a lemon grove near Irvine, California. Treatments were applied on May 6 by handgun (450 psi) with about 1350 gal per acre; four two-tree replicates per treatment. At one end of this plot four materials were applied with low volume equipment at 100 gal per acre; four four-tree replicates per treatment. Five buds on each of four terminals were dissected for each replicate, and the percent buds infested was calculated. Pretreatment infestation levels averaged close to 40% in each treatment.

Several acaricides were tested for efficacy against citrus rust mite (CRM). Each treatment was replicated 3 times in 2-tree plots (except only 2 plots for Vendex at the 1.5-oz rate). Trees were assigned to a replicate on the basis of their prespray CRM infestation level. Trees were sprayed on May 1 with a Hardy orchard spray gun (No. 8 orifice) at 500 psi, using ca. 15 gal/tree (1600 gal/acre). On each count date, 10 green lemons (picked from within the canopy of the tree) were rated as infested or not. Lemons were examined with a 10X handlens: The path made with the lens was a circle 4 cm in diameter centered on the stem, plus a line from stem to the opposite end of the lemon.

A number of materials were tested for efficacy against citrus red mite in a lemon grove in Riverside, California. Treatments were applied on Apr 28-29 by handgun (450 psi) with about 1200 gal per acre. Naked eye counts of mites on 32 leaves per tree (two 4-leaf terminals per quadrant) were made. There were four single-tree replicates.

Under a program in which demeton was used in a California lemon grove to control citrus red mite, Panonychus citri (MeG.), and parathion was used to control California red scale, Aonidiella aurantii (Mask.) , the citrus red mite developed resistance to demeton applications. Laboratory evaluations showed that mites resistant to demeton were also resistant in varying degrees to 14 other organic phosphates. It required ]5,000 and 80,000 times the concentration of Trithion, and only 8 and II times the concentration of Bio 1240 (Bis 5-(diethoxyphosphinothioyl) mercapto methane) in the spray to deposit sufficient residues to effect 50% and 95% mortalities, respectively, in the resistant strain of mites as compared to the nonresistant. In field tests during 1957 those materials known to be effective in controlling nonresistant citrus red mites were ineffective in groves where resistance had developed through the use of both demeton and parathion.

Trees were sprayed on Apr 13-14 by hand-gun (ca 1200 gal per acre). There were 4 single-tree replicates. Naked-eye counts of mites on 32 leaves per tree (two 4-leaf terminals per quadrant) were made.

A number of acaricides were tested for efficacy against citrus red mite in a lemon grove in Riverside, California. Treatments were applied on Apr 23-24 by handgun (450 psi) with about 1200 gal per acre, or 10-15 gal per tree. There were four single-tree replicates per treatment. Adult female mites were counted on 32 leaves per tree (8 terminals).

Materials were tested for efficacy against citrus bud mite in a lemon grove near Irvin, California. Treatments were applied on Sep 16 by handgun (450 psi) with about 1500 gal per acre. There were four two-tree replicates and pre-treatment levels varied from 48.8 to 71.3 percent buds infested. Five buds on each of four terminals were dissected for each of the replicates, and the percent buds infested was calculated. At the time of treatment, there was only a trace of citrus red mite; the population was monitored on a few trees and at 100 days post-spray a rating of all trees was made.

Several acaricides were tested for efficacy against citrus red mite (CRM). Each treatment was replicated 3 times in single-tree plots. Trees were assigned to a replicate on the basis of their prespray CRM infestation level. Trees were sprayed on April 21 with a Hardy orchard spray gun (No. 8 orifice at 500 psi using ca. 12.5 gal/tree or 1350 gpa). On each count date, the CRM adult females were counted on 32 leaves/tree (8 four-leaf terminals, 2/quadrant).

Materials were tested for efficacy against the citrus bud mite in a 23-year-old lemon grove (NW-SE rows, 24 ft × 19 ft spacing) in Field 7 of the U.C. South Coast field Station near Irvine, CA. Treatments were applied May 26 using a Kinkilder low-volume mist sprayer with attached 10-foot citrus tower at approximately 100 gal per acre. Each material was applied to 2 adjacent 16-tree rows with 4 trees randomly chosen for each material as permanent data trees. Four young terminals were chosen from each sample date from the inner row side of each data tree. On each terminal, 5 buds were dissected and the percent infested buds was calculated.

Acaricides were applied in a lemon grove infested with citrus red mite. Treatments were applied by handgun (450 psi) with about 1500 gal/acre. There were six single-tree replicates per treatment. Adult female mites were counted on 32 leaves per tree (8 terminals).