PEST MANAGEMENT AND SAMPLING Sampling Plan for Dicyphus hesperus (Heteroptera: Miridae) on Greenhouse Tomatoes 1 2 JUAN ANTONIO SANCHEZ SANCHEZ, ROBERT R. MCGREGOR, AND DAVID R. GILLESPIE PaciÞc Agri-Food Research Centre, Agriculture and Agri-Food Canada, P.O. Box 1000, Agassiz, BC, Canada V0M 1A0 Downloaded from https://academic.oup.com/ee/article/31/2/331/347666 by guest on 27 September 2021 Environ.Entomol.31(2): 331Ð338 (2002) ABSTRACT Dicyphus hesperus Knight has good potential as a biological control agent for green- house pests in greenhouse tomato crops.The spatial distribution of D. hesperus was studied and a sampling plan was developed to monitor this species in greenhouse-grown tomatoes.Adults and nymphs are distributed in a more aggregated pattern among plants than within plants.The strong, signiÞcant relationship between the mean population density and the proportion of occupied sample units (leaves or plants) makes it possible to use a binomial or presence-absence sampling approach. Presence-absence sampling is an efÞcient method for crop management purposes because less time is needed to process the samples compared with a method where all insects are counted.At high densities, considering a sample unit to be occupied only when there are more than a determined number of individuals reduces considerably the optimum sample size required. KEY WORDS Dicyphus hesperus, spatial distribution, binomial sampling Dicyphus hesperus KNIGHT is an omnivorous predator rolophus caliginosus Wagner, Dicyphus tamaninii Wag- that is under development as a biological control agent ner, and Cyrtopeltis (Engytatus) modestus (Distant) for arthropod pests of greenhouse-grown tomatoes in (Tanada and Holdaway 1954, Alomar and Albajes British Columbia, Canada (McGregor et al.1999, 2000; 1996, Malausa and Trottin-Caudal 1996, Sampson and Gillespie and McGregor 2000).Adults and nymphs Jacobson 1999).Because of its role in pest manage- may also feed on and cause damage to tomato fruits ment and its potential to damage tomato fruits, it is under certain conditions (McGregor et al.2000).Con- particularly important that an adequate sampling sequently, populations of D. hesperus on the crop need method be available for D. hesperus to monitor pop- to be monitored more closely than other biological ulations after releases.For example, D. tamaninii typ- control agents, and a simple and accurate approach to ically damages tomato fruits when predator popula- sampling is required. tions are high and whiteßy populations are low Nymphs of D. hesperus readily complete their (Alomar and Albajes 1996).Chemical controls may be growth and development on either the greenhouse applied against this predator when these conditions whiteßy, Trialeurodes vaporariorum (Westwood) exist and the probability of damage to the crop is high (Homoptera: Aleyrodidae), or twospotted spider (Alomar and Albajes 1996). mites, Tetranychus urticae Koch (Acari: Tetranychi- The choice of an appropriate sample unit is one of dae) (McGregor et al.1999), two of the primary pests the Þrst problems in designing a sampling plan.The of greenhouse tomatoes in British Columbia.In addi- selection of the sample unit will affect estimates of the tion to feeding on these prey species, D. hesperus population size.Broadbent (1948 in Southwood 1978) nymphs and adults also feed on plant material observed that the choice of the plant or the leaf as the (Gillespie and McGregor 2000, McGregor et al.2000). sample unit for determining the population density Plant feeding in D. hesperus apparently functions to affected estimates of the population levels of Myzus acquire the water necessary for extra-oral digestion of persicae (Sulzer) in potato crops.Shipp et al.(1992) prey (Gillespie and McGregor 2000).In the absence compared the absolute population size of Orius spp., of tomato leaves or other sources of water, D. hesperus obtained by counting all individuals on whole pepper cannot feed on prey or complete nymphal develop- plants, with results from both leaf and ßower samples ment (Gillespie and McGregor 2000). and concluded that the ßower samples were better Damage to tomato fruits has been reported for a related with the absolute counts. number of other omnivorous mirid species like Mac- Once the sample unit has been established, several sampling methods can be adopted.Counting the total 1 Department of Biology, Douglas College, P.O. Box 2503, New number of individuals present in a sample unit is a Westminster, BC, Canada V3L 5B2. commonly used technique in research, although this 2 E-mail: [email protected]. may be expensive and impractical for pest manage- 332 ENVIRONMENTAL ENTOMOLOGY Vol.31, no.2 ment monitoring.Binomial, or presence-absence sam- peripheral single, guard rows of 20 plants each.The pling techniques, that are based on the relationship rows were parallel to the long axis of the greenhouse. between population density and spatial distribution Whiteßies were introduced in two batches of 500 represent a good alternative.Sampling methods have adults each, once on 19 February 1999 and again on 25 been developed for a number of pests and predatory February 1999.They were dispersed evenly through arthropods based on presence-absence schemes the crop. Dicyphus hesperus adults were introduced on (Nachman 1984, Raworth 1986, Raworth and Merkens 15 March 1999 (400), 19 April (400), 26 April (400), 1987, Nyrop et al.1989, Binns and Bostanian 1990, and 3 May (1000) and were also dispersed evenly. Frazer and McGregor 1990, Sanchez et al.1997). Sulfur dust was applied to the ßoor to control powdery The knowledge of the spatial distribution provides mildew, and SaferÕs insecticide soap (SaferÕs Ltd., information about the biology of the organisms and Scarborough, Ont.) was applied at label rates to the can be used to develop binomial or presence-absence top 10 leaves on 17 May to control excessive numbers sampling methods.A negative binomial relationship is of whiteßy adults.In the second growing season seed- Downloaded from https://academic.oup.com/ee/article/31/2/331/347666 by guest on 27 September 2021 a theoretical function that is commonly used to de- lings (ÔRhapsodyÕ) were transplanted on 18 January, scribe aggregated distributions in insect populations arranged in one central double row of 40 plants and (Bliss and Fisher 1953).The Poisson distribution is two peripheral single guard rows of 20 plant in each more appropriately used to describe populations that compartment.Whiteßies were introduced at 100 are randomly distributed (Southwood 1978, Garcia- adults/compartment on 3 February 2000 and D. hes- Mari et al.1994, Sanchez et al.1997).Presence-ab- perus at 100 adults/compartment 20 d later.Both sence sampling methods are highly practical for pest whiteßy and D. hesperus were introduced evenly management purposes because of the substantial re- through the crop. duction in the time required to process samples com- Sampling and Data Collection. In 1999, 18 plants per pared with complete count samplings.Besides the week were sampled by selecting six plants randomly theoretical distribution functions, an empirical model from each double row each week.Plants were not based on experimental data can also be used to de- sampled again until all plants had been sampled.After scribe the relationship between the density and the all plants had been sampled, we rerandomized the proportion of occupied sample units (Kono and plant numbers and continued selecting samples as Sugino 1958, Gerrard and Chiang 1970, Nachman above.In 2000, 21 plants were sampled from each of 1984).At high densities the binomial method does not the four compartments using the same routine previ- accurately estimate population size.When this occurs, ously described.Plant and leaf samples were collected the binomial method can be modiÞed by increasing in each of 27 wk during the 1999 growing season and the threshold at which the sample unit is considered in each of 20 wk during the 2000 growing season. to be occupied (e.g., tally threshold, T Ͼ 2).This Two types of samples were taken from each sample alternative makes binomial sampling practical at plant.First, all of the D. hesperus adults and nymphs on higher densities and may also improve the accuracy of each sampled plant were counted visually in situ the method (Gerrard and Chiang 1970, Binns and (hereafter called “plant samples”).Second, a single Bostanian 1990). leaf was randomly selected, and cut and bagged indi- In this study we analyzed 2 yr of data from D. vidually from each of the upper, middle and bottom of hesperus releases in tomato greenhouses.Our objec- the plant on the Þrst year (hereafter called “leaf sam- tive was to study its spatial distribution and to develop ples”).In the second year a single leaf was randomly a sampling method that could be used by researchers, selected from the middle level and was cut and pest managers, and greenhouse growers to determine bagged.These leaves were carried to the laboratory the population density of D. hesperus in greenhouse where all of the D. hesperus nymphs and adults were tomato crops. counted. Data Analysis. Selection of the Sample Unit. In our analysis we assumed that plant samples were a good Materials and Methods estimation of the absolute population size.Although Crop History. Samples were taken during the 1999 these plant samples are subject to sample error, the and 2000 growing seasons from tomatoes (Lycopersi- population of tomato plants is composed of individuals con esculentum Mill.) grown in greenhouses at the with similar characteristics and theoretically equal PaciÞc Agriculture and Agri-Food Research Center in probabilities of being colonized.On the leaves, D. Agassiz (British Columbia).In the Þrst year the green- hesperus may be unevenly distributed depending on house compartment was 12 by 6.4 m, with a trellis wire the location within the plant.Therefore, the estima- height of 2.9 m.