16 Plant Protection Quarterly Vo1.1 3(1) 1998 Sampling method Samples were obtained using a Ryobi Sweeper Vac (model RSVllOOA MKll) vacuum sampler modified according to Research reports Wright and Steward (1992). An empty sampling bag was placed in the vacuum sampler before each sample was taken. Ten samples at each site were taken at monthly intervals from September 1993 to The effect of non-crop vegetation on the insect pests October 1994 by applying the va cuum sampler to 30 flushing shoots from each of and their natural enemies in cashew (Anacardium five cashew trees at the middle level of the L.) tree canopy. At each sampling occasion, a occidentale plantations total of fifty evenly distributed trees were sampled at each site. The samples were R.K. Peng, K. Christian and K. Gibb, Faculty of Science, Northern Territory then frozen. After 24 hours, a ll the arthro­ University, Darwin, Northern Te rritory 0909, Australia. pods in each bag were transferred into a bottle containing 70% ethanol fo r later ex­ amination. Abstract could provide a reservoir of natural en­ Trophic studies In order to introduce an integrated pest emies that may regulate insect pests in A flexible netting bag (45 x 28 x 18 cm) management program in cashews, the ef­ cashew plantations. The most important was used to confine insects to an a rea on fect of non-crop vegetation on the arthro­ predators of the main cashew insect pests flushing shoots of a field cashew tree to pod fauna in cashew plantations in tropi­ are green ants, Oecophylla smaragdilla determine the food habits of a variety of cal northern Australia was studied by (Fabricius) (Peng el al. 1995). The specific arthropod species under realistic condi­ taking regular vacuum samples. Where aims of this stud y were: tions. With this technique we could check cashews had rich understorey and were i. to assess whether proximity to non-crop the bag easily and transfer it to fresh flu sh­ closely surrounded by non-crop vegeta­ vegetation can increase the diversity of ing shoots when the condition of the flush­ tion, the diversity of arthropods, the ra­ arthropods, ing shoots inside the bag became poor tio of the total natural enemy numbers to ii. to determine whether non-crop vegeta­ due to insect feeding. This system was insect pests and the average yield were tion can enhance natural enemy popu­ used in four cashew phenological periods; significantly higher than where cashew lations in cashew plantations, espe­ pre-flowering (March-April), fl owering trees had no understorey and were iso­ cially the green ant population and (May- June), flowering and fruiting Oune­ lated from non-crop vegetation. We sug­ iii.todetermine whether there is a relation­ August) and ordinary flush (September­ gest that the close proximity of non-crop ship between the proximity of non-crop October) from September 1993 to August vegetation enriches the diversity of vegetation and crop yield. 1995. To determine the relationship be­ arthopods in cashew plantations by pro­ tween insect pests and their predatory ar­ viding a reservoir of natural enemies that Materials and methods thropods, each predatory species together naturally regulate insect pests and re­ with each species of insect pest was intro­ sults in an increased crop yield. Study sites duced into the bag which covered two ar­ Two study sites were used for this study: thropod free flushing shoots. These bags Introduction a two hectare section of eight-year-old were checked once a day for two days. Pi.lot cashew plantations in the Northern cashew trees a t the Wildman River Planta­ Eight fie ld observations were made to ob­ Territory of Australia have been subject to ti on (12 0 64·S, 131 0 8TE) and a two hectare serve the feeding behaviour of the main serious insect pest problems since 1988 stand of six-year-old cashew trees at the insect pests and their natural enemies dur­ (Houston and Malipatil 1991, Peng el al. Howard Springs Farm (12 0 49·S, 131 0 ing the insect pest outbreak of 1994 and 1995, Stonedahl el al. 1995). Consequently, 04'E). The Wildman River site is 90 km 1995. Observations were made during insecticides have to be regularly used to east of Howard Springs. The planting pat­ three periods (early morning, noon and ! control insect pests such as He/opeitis terns of cashew trees at both sites were early evening) and each period lasted pernicia/i, (Stonedahl. Malipatil and Hou­ similar, and both sites experienced the 1-1.5 hours. ston), Amblype/ta IIIleseell s (Distant) and same tropical wet-dry climate. The study Pellicillaria jocosatrix (Guenee). Insecticides site at Wildman River was in the centre of Arthropod identification can lead to a reduction in insect pest para­ 16 hectare of cashews (370 m away from Known cashew insect pests and their site and predator populations as well as non-crop vegetation) and had not received natural enemies were identified to species. in sect pollinator populations. It is there­ pesticides since June 1993. The study site Other arthropods were identified to spe­ fore very important to explore alternative at Howard Springs had not received pesti­ cies, genera, sub-family or family level. control methods. cides since April'1993 and was closely sur­ Cashew plantations in the Northern rounded by non-crop vegetation. At the Yield assessment Territory of Australia are surrounded by Wildman River site, ground vegetation To harvest cashews, growers wait for the non-crop vegetation such as Acacia, Euca­ under cashew trees was sparse, contain­ nuts to drop on the ground before they are lyptus, Erythrophleums, Planc110nia and ing only a small amount of grass picked up by a vacuum harvester. Eight Buchanania. The 'natural enemy hypoth­ Pellll i,etu", polys/aeilioll (L.) Schultes be­ trees at each site were randomly chosen esis' predicts that there will be a greater tween weeding periods. At the Howard for yield assessment. At the beginning of abundance and diversity of natural en­ Springs site, the ground vegetation was the fruit setting period, fallen leaves, tvvigs emies of pest insects in polycultures com­ dense and rich, dominated by P. and grass under each tree were cleared to pared to monocultures (Root 1973). We polystaeilioll, Sida spp., ealopogonill'" facilitate a late harvest. All the nuts under wished to determine whether the presence ","eunoide, (Desv.), Passifiora foelida (L.) each tree were coUected by the vacuum of non-crop vegetation near cashew trees and Hyplis sauveolells (L.) Poit. harvester and weighed separately. Plant Protection Quarterly VoI.13(1) 1998 17 Climatic data Table 1. Similarity measurement of the richness of non-crop trees close to The microclimatic data at the Wildman cashew plantations, the main insect pests and their natural enemies in River Plantation were taken from the cashew plantations between Wildman River Plantation (WRP) and Howard records of a meteorologica l stati on inside Springs (HS). the cashew plantation. The microc1imatic data at the Howard Springs site were from Type Number of species Number of species in C j the records of the meteorological station of WRP HS common between two sites Howard Springs Nature Park, 5 km from Non-crop trees 24 27 22 0.76 the study site. Insect pests 11 11 11 1.00 0.88 Statistical analysis Natural enemies 21 24 21 All the arthropods ca ught by the vacuum sampler were included in the statistical Table 2. Comparisons of the mean temperature, the mean relative humidity comparisons. The log-series index (0.) and the rainfall between Wildman River Plantation (WRP) and Howard (Fisher e/ a/. 1943) was used for the analy­ Springs (HS) from October 1993 to October 1994 using paired sample t tests. sis of diversity: S ~ 0: In(1 + N/o:), where S = number of taxa and N = number of indi­ Type Site Mean ± SEM Difference between P viduals. The greater the value of 0.., the means ± SDD more diverse is the community. The Ave. temperature (OC) WRP 26.7 ± 0.8 -0.277 ± 0.559 -1.788 0.101 Jaccard equation, C) = j/(a+b-j), was used HS 27.0 ± 0.7 to measure similarity between non-crop Ave. relative humidity (%) WRP 66.8 ± 2.9 -1.000 ± 2.582 -1.396 0.188 trees, insect pests and their natural en­ HS 67.8 ± 2.9 j = emies between the two sites, where the Rainfall (mm) WRP 94.8 ± 31.8 ·0.705 ± 1.273 -1.662 0.135 number of species in common at both HS 146.2 ± 57.9 sites, a or b = the number of species which occurred at each site (Southwood 1978). The value of C ranges from 0- 1, and the J 50 bigger the value, the more similar the two sites. The ratio data of natural enemies to pests were transformed to arcsine square root. and the rainfall data were trans­ fo rmed to natural logarithm before statis­ 40 tica l tests were applied. Paired sample t tests were used to compare the arthropod diversity, the ratio of natural enemies to insect pests and the microclimatic factors '3',..., between the two study sites. A group sam­ ..~ 30 I- ple t test was used to compare the yields ~ of the two sites. .5 .t> Results .; .. 20 I- .~ Similarity of biological and physical Q factors between two sites The numbers of non-crop tree species present between the two sites were statis­ 10 tically equivalent (C j ~ 0.76, Table 1), and the fauna of the main in sect pests and natural enemies in cashew plantations was also equivalent (CJ = 1 and 0.88 re­ spectively, Table 1).