Crop plant compensation for herbivory and the population dynamics of herbivores are two key elements in defining an herbivore's pest status. We studied the dynamics of natural, unmanipulated populations of the aphid Aphis gossypii on seedling plantings of cotton, Gossypium hirsutum and Gossypium barbadense, over a 4‐year period in California's Central Valley. Aphid populations colonized all plantings, but reached densities in excess of 0.5 aphids/leaf during only one year (1991), when outbreaks occurred. Outbreak populations were, however, ephemeral; predation and parasitism suppressed aphid populations prior to the initiation of flower bud production, when cotton plant growth may become photosynthate‐limited. Effective natural biological control was observed despite the action of hyperparasitoids and the heavy mortality of immature parasitoids that occurred when predators consumed parasitized aphids.

Efficacy of the selective acaricides dicofol (960 g a.i./ha) and propargite (1,500 g a.i./ha) for control of twospotted spider mite, Tetranychus urticae Koch, on cotton was compared to profenofos (750 g a.i./ha), a broad-spectrum acaricidal organophosphate which was the industry standard. Ground and aerial applications of propargite reduced mite populations to lower levels for longer than the other compounds. Ground applications of dicofol and profenofos provided equivalent efficacy, but it was only about half that of propargite. A side dressing of the granular insecticide aldicarb (1,500 g a.i./ha) was included at one site and, although it suppressed mite populations, was less efficacious than propargite and uneconomic for commercial use. Dicofol and propargite are now registered for commercial use in cotton. Results of laboratory bioassays suggest that T. urticae populations collected from several cotton farms in New South Wales are presently susceptible to both compounds. The incorporation of these products into the insecticide resistance management strategy for cotton is discussed.

Sublethal effects of acephate (an organophosphate) and biphenate (a pyrethroid) on greenhouse whitefly (Trialeurodes vaporariorum Westw.) were investigated by measuring male and female longevity, daily rate and lifetime fecundity per female, and egg viability for cohorts exposed to LC50s when Acala SJ‐2 cotton was a host. Males T. vaporariorum were more sensitive to sublethal concentrations than females. Significant reductions in male longevity were caused by exposure to acephate and biphenate, whereas female longevity was not significantly affected by exposure. Exposure to biphenate and acephate treatments reduced lifetime fecundity by 29% and 37%, respectively. Viability of eggs laid by treated females was not affected. Analysis of patterns and heterogeneity of reproduction suggests that timing and magnitude of oviposition, average level of daily oviposition and reproductive decline were influenced by sublethal concentrations of insecticides. Results of repeated‐measures analysis of variance confirmed reductions in fecundity of females T. vaporariorum exposed to sublethal concentrations.

Lygus bug, Lygus hesperus Knight, and beneficial insect populations (Orius sp., Geocoris spp., and Nabis spp.) were quantified in alfalfa strips, which were interplanted within cotton fields. The propensity of alfalfa strips to retain lygus bugs, thereby keeping them out of cotton, and the utility of alfalfa strips as a reservoir for beneficial insects were evaluated from May to August in 1990 and 1991. The following three alfalfa cutting strategies were examined: (1) uncut alfalfa, (2) a 28-d strip-cut treatment, and (3) a 35-d strip-cut treatment. Insect populations were quantified in both the newer alfalfa growth and the older alfalfa growth of the strip-cut treatments. Lygus bug densities were significantly higher in the uncut treatment than in the other treatments, peaking at 520 per 1.9 m2 in 1990 and 350 per 1.9 m2 in 1991. Lygus bug levels in the strip-cut treatments were low in the newer alfalfa growth (averaging 41.8 per 1.9 m2) and only slightly higher in the older alfalfa growth of the 28-d strip-cut treatment (averaging 65.3 per 1.9 m2). Populations were relatively constant within these three treatments throughout the season. However, in the older growth of the 35-d cutting regime, Lygus bug populations averaged 103 per 1.9 m2. Densities of beneficial insects were also higher in the uncut than the strip-cut treatments, but the higher predator densities apparently did not offset the high Lygus bug population increase. The uncut treatment also lacked Lygus bug egg and nymphal mortality from the alfalfa cutting as compared with the strip-cut treatments. The less frequent cutting, in the 35-d compared with the 28-d treatment, probably also allowed for a buildup of the Lygus bug population. Lygus bug instar distribution, sex, and predator species were also examined in these treatments. It appears that to optimize Lygus bug management, while still producing high densities of predacious insects, strip-cut alfalfa should be used and cut on a 28-d schedule.

Realized heritability (h2) of resistance to dicrotophos in greenhouse whitefly, Trialeurodes vaporariorum Westwood, was estimated from a laboratory selection experiment. Five generations of selection increased the LC50 approximately 13-fold. Estimated h2 of resistance to dicrotophos was 0.40 when calculated with the method of Tabashnik (1992) and 0.35 with the method of Tanaka & Noppun (1989). These results suggest that 35 to 40% of the total phenotypic variation in resistance was caused by additive genetic variation. For thirteen previously reported estimates of h2 of insecticide resistance in other insect pests, the mean was 0.29. The relatively high h2 of dicrotophos resistance for T. vaporariorum is consistent with rapid resistance development in field populations.

Susceptibility of fie d populations of greenhouse whitefly, Trialeurodes vaporariorum Westwood, in the San Joaquin Valley (California) cotton cropping system was tested with laboratory bioassays with acephate and dicrotophos. Approximately 9.5-fold resistance to acephate and 18.5-fold resistance to dicrotophos were detected. Results of bioassays indicated that 56.2 ppm acephate and 316 ppm dicrotophos could serve as discriminating concentrations for detecting resistant T. vaporariorum populations. Field trials demonstrated lack of control with acephate and dicrotophos in resistant T. vaporariorum. Susceptibility levels to acephate and dicrotophos of 32 T. vaporariorum field populations collected from cotton and other hosts including weeds in Kern, Kings, and Tulare counties were estimated by bioassays with discriminating concentrations. Substantial regional variability in susceptibilities to the two pesticides was found. Resistant and susceptible T. vaporariorum phenotypes occurred on cotton and other cultivated or weed hosts. Cross-resistance between acephate and dicrotophos is suggested. Implications of these results for integrated pest management of cotton system in the San joaquin Valley are discussed.

The relationship between insecticide resistance and fitness parameters in greenhouse whitefly was assessed by examining longevity and fecundity in seven organophosphate-resistant and susceptible colonies on six plant hosts representing common cultivated plants and weeds in the San joaquin Valley (SJV), Calif., cotton system. All colonies had higher fecundity and longevity on common bean (cultivar Sal) and cheeseweed than on cotton cultivars, whereas on tree tobacco longevity and fecundity were lowest. Within cotton cultivars, Pima S-6 was a better host than Acala SJ-2 and L-3940. There was no indication of host races in greenhouse whitefly as suggested by the lack of significant colony by host interactions. Longevity was equivalent in organophosphate-susceptible and resistant colonies. Fecundity in the resistant colonies was higher than in the susceptible colonies. Thus, there was no obvious fitness disadvantage associated with resistance to insecticides in greenhouse whitefly. Implications of cultivated and weed hosts with respect to resistance amplification and resistance management for greenhouse whitefly in the SJV cotton system are discussed.

Laboratory experiments were conducted using organophosphate-resistant and susceptible strains of greenhouse whitefly, Trialeurodes vaporariorum Westwood, to assess age-specific vital rates in individually-held adults, and development and survival in preadults on three cotton cultivars at 27 +/- 1-degrees-C, 50 +/- 10 % RH, and a photoperiod of 16:8 (L:D). Female whiteflies lived longer than males, with a maximum life expectancy of 29 days. Heaviest egg laying occurred at ages between 7 and 18 days when individual whiteflies laid > 10 eggs/day. Greenhouse whitefly populations doubled weekly, with stable age distribution of 63 % eggs, 28 % larvae, 5 % pupae, and 4 % adults. Analysis of various life history parameters that combine aspects of survival, developmental rates, and fecundity indicated no consistent differences in reproductive fitness between the two greenhouse whitefly strains. Of the three cotton cultivars tested, Pima S-6 was most susceptible, Acala SJ-2 was intermediate and Gumbo 500 was most resistant to greenhouse whitefly. Resistance of Gumbo 500 was expressed as slower developmental rates, reduced survival to adulthood, lower reproductive rates, and lower intrinsic rate of increase.

Journal Article Pesticides and Cotton: Effect on Photosynthesis, Growth, and Fruiting Get access R. R. Youngman, R. R. Youngman Department of Entomology, University of California, Riverside, California 92521 Search for other works by this author on: Oxford Academic PubMed Google Scholar T. F. Leigh, T. F. Leigh Department of Entomology, University of California, Riverside, California 92521 Search for other works by this author on: Oxford Academic PubMed Google Scholar T. A. Kerby, T. A. Kerby Department of Entomology, University of California, Riverside, California 92521 Search for other works by this author on: Oxford Academic PubMed Google Scholar N. C. Toscano, N. C. Toscano Department of Entomology, University of California, Riverside, California 92521 Search for other works by this author on: Oxford Academic PubMed Google Scholar C. E. Jackson C. E. Jackson Department of Entomology, University of California, Riverside, California 92521 Search for other works by this author on: Oxford Academic PubMed Google Scholar Journal of Economic Entomology, Volume 83, Issue 4, 1 August 1990, Pages 1549–1557, https://doi.org/10.1093/jee/83.4.1549 Published: 01 August 1990 Article history Received: 28 October 1988 Accepted: 01 March 1990 Published: 01 August 1990

Cotton test plots treated with the selective acaricides propargite, avermectin B1 or left untreated showed that a Tetranychus urticae Koch population can cause loss of efficacy of propargite. In contrast, test plots infested with mixed species and resistance levels of Tetranychus species were maintained closer to economic thresholds by propargite. A rapid bioassay for detection of T. urticae and T. pacificus McGregor populations resistant to propargite was developed. Comparison of the rapid with the standard leaf bioassay method using discriminating concentrations of 1,000 and 3,162 ppm resulted in the same prediction of significant levels or frequencies of propargite resistance in 86.7 and 88.7% of the replications tested. A threshold of <70% mortality with a discriminating concentration of 1,000 ppm propargite was chosen for the rapid test to identify spider mite populations that are most likely to cause field efficacy problems. The rapid propargite bioassay was used in combination with sampling of cotton leaves to show that it can be used commercially to evaluate the severity of propargite resistance in individual fields.

Three insecticides currently registered for L. hesperus control on cotton (Gossypium hirsutum L.) were tested in the laboratory to determine topical LD30 values. Adult bugs of unknown age were collected from hay alfalfa (Medicago sativa L.) at 3 locations in the San Joaquin Valley, Calif., and held on snap bean (Phaseolus vulgaris L.) pods for 20 h. After aspiration into groups of 10 and anesthesia with 10 s of COa, a 1-p.l droplet of insecticide-acetone solution was applied to the coxal area of the thorax. Four groups of each sex were treated with each dosage; mortality was determined at 24 h. Data were averaged and corrected by Abbott's formula for probit analysis.

Reproductive fitness of the flower thrips, Frankliniella occidentalis (Pergande), was much lower on leaves of a cotton variety resistant to spider mites, Tetranychus urticae Koch, than on leaves of a spider mite-susceptible variety. The addition of mite eggs or pollen to cotton leaves significantly improved several fitness traits of flower thrips. Pollen was nutritionally better than mite eggs. The addition of pollen lowered the time from egg to adult, increased fecundity, and improved longevity over that which occurred on leaf tissue alone. The effect of pollen was more pronounced on resistant than on susceptible leaves. Pollen raised the intrinsic rate of increase (r) by 0.063 on susceptible leaves and by 0.202 on resistant leaves. When pollen is available, flower thrips can completely overcome the negative effects of resistant leaves.

Numbers of Lygus Hesperus Knight per 50 net sweeps and numbers of abscised and lygus bug damaged squares per cotton plant terminal were counted weekly. Square abscission and square damage showed a high positive correlation with L. hesperus numbers (r = 0.92, n = 7, for week of count and r = 0.69, n = 63, for June through July) and with square age (r = 0.96, n = 20); fruit set on first and second sympodial branch positions showed a high negative correlation with L. Hesperus numbers (r = -0.65, n = 25, for zero to six bugs per 50 sweeps). Comparisons of the proportion of squares damaged by lygus bugs between the terminal 5 nodes, terminal 10 nodes, and all nodes on one to three dates per location indicate that the terminal 5 nodes provide a reliable estimate of L. Hesperus feeding damage to squares. Our calculations indicate that before 1 August each lygus bug collected in the sweep net indicates a potential for 23,400 abscised plus damaged squares per hectare on the day of sample. Boll retention in relation to lygus bug numbers is presented. This information is expected to provide guidance when developing management strategies for L. hesperus on cotton. Square damage and loss can be used to estimate need for pesticide use and for refining the lygus bug: square ratio as an estimator of treatment threshold.

Journal Article Laboratory and Field Investigations of Spider Mite (Acari: Tetranychidae) Resistance to the Selective Acaricide Propargite Get access T. J. Dennehy, T. J. Dennehy 1 Department of Entomology, University of California, Davis, California 95616 1Current address: Dep. of Entomology, New York State Agric. Exp. Stn., Cornell Univ., Geneva, NY 14456. Search for other works by this author on: Oxford Academic PubMed Google Scholar J. Granett, J. Granett Department of Entomology, University of California, Davis, California 95616 Search for other works by this author on: Oxford Academic PubMed Google Scholar T. F. Leigh, T. F. Leigh Department of Entomology, University of California, Davis, California 95616 Search for other works by this author on: Oxford Academic PubMed Google Scholar A. Colvin A. Colvin Department of Entomology, University of California, Davis, California 95616 Search for other works by this author on: Oxford Academic PubMed Google Scholar Journal of Economic Entomology, Volume 80, Issue 3, 1 June 1987, Pages 565–574, https://doi.org/10.1093/jee/80.3.565 Published: 01 June 1987 Article history Received: 01 August 1986 Published: 01 June 1987 Accepted: 23 December 1987

Artificially inoculated spider mite foci increase in size at an exponential rate. Productivity was greatest on plants farthest from the center of each focus. Timing of initial infestation was shown, both experimentally and through simulation, to affect ultimate yield of cotton: the earlier the initiation of infestation, the lower the yield. These results as well as those of other researchers indicate that the tolerance of cotton to mite infestations increases with crop maturity.

Spider mites were collected from cotton at 36 locations in the San Joaquin Valley of California, both before propargite had been applied and again late in the season. All populations of Tetranychus turkestani Ugarov & Nikolski, the dominant early season spider mite, were susceptible to propargite. Populations of Tetranychus urticae Koch and Tetranychus pacificus McGregor exhibited a variety of responses from highly susceptible to highly resistant. These levels of resistance were defined by the range and homogeneity of response. Early season T. urticae populations were predominantly susceptible. Late-season collections of T. urticae from the same locations exhibited lower, equal, or increased tolerance to propargite, suggesting instability of resistance. Early and late-season collections of T. pacificus exhibited a consistently higher and narrower range of response to propargite than T. urticae , suggesting a possible natural tolerance to propargite. Field plots demonstrated lack of control with propargite when populations were composed of resistant T. pacificus alone. Cases of multiple resistance to propargite and dicofol were found for both T. urticae and T. pacificus.

The plant bug, Lygus hesperus Knight, was reared on five common bean, Phaseolus vulgaris (L.), genotypes, three of which were previously identified as resistant (‘BAT 1081’, ‘BAT 1299’, and ‘CIAT 5979’) and two as susceptible (‘Red Kidney’ and ‘CIAT 5683’). Age-specific life-table parameters were estimated as a means to measure plant resistance to L. hesperus. Under both field and laboratory conditions, fewer bugs survived to the adult stage on the resistant cultivars than on the susceptible cultivars. Female lygus bugs reared on the resistant genotypes also had lower gross reproductive rates, net reproductive rates, and intrinsic rates of increase than those bugs held on the susceptible genotypes. These life-table values for CIAT ‘;5683’ were significantly greater than for all other cultivars. Resistance had no effect on mean generation time. Finite rates of increase and population doubling times were significantly lower on resistant cultivars. These life-table results confirm resistance to lygus bugs in common bean cultivars based on reduced survivorship to adulthood, fecundity, and longevity of females.