|
Section D: Natural Enemy Ecology, and Biological Control (Part Two) - 1999
Investigator's Name(s): Steven E. Naranjo.
Affiliation & Location: USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ.
Research & Implementation Area: Section D: Natural Enemy Ecology and Biological Control.
Dates Covered by the Report: January - December 1998
Potential Interactions Between Predators and Parasitoids of Sweetpotato Whitefly
A study was initiated to examine the extent to which a general predator would prey on parasitized Bemisia tabaci. Geocoris punctipes adult females were provided an equal number of parasitized (Eretmocerus emiratus) and unparasitized 4th instar whiteflies (42 total) in petri dishes and allowed to forage for 24 h at 27°C. Studies were replicated 12 times with early instar parasitoids (displacement of host mycetomes) and 16 times with pupal-stage parasitoids. Preliminary results indicate that G. punctipes was about 1.3 times more likely to prey on parasitized compared with unparasitized whiteflies when presented with an equal number of both. This pattern was evident regardless of immature parasitoid age. The slight preference for parasitized whiteflies may be partially due to the fact that parasitized hosts often swell and may be more apparent to foraging predators. Further studies are planned with Orius tristicolor and Collops vittatus, two other common predator species in central Arizona. These data will aid ongoing efforts to model biological control of B. tabaci in cotton, and help to more accurately estimate marginal mortality rates due to parasitism in ongoing life table analyses.
Investigator's Name(s): M. R. V. Oliveira & D. Návia.
Affiliation & Location: Embrapa - Recursos Genéticos e Biotechnologia, Cx. Postal 02372, CEP: 70.849-970, Brasília, DF. Brazil.
Research & Implementation Area: Section D: Natural Enemy Ecology and Biological Control.
Dates Covered by the Report: January - November 1998
Prospection and Evaluation of Natural Enemies of Bemisia tabaci (Biotype B)
In the last three years, the biotype B of B. tabaci has spread to all five regions of Brazil. The northeastern region has suffered more than the others the attack of this insect, because of climate conditions and abundance of host plants. The losses caused by the whitefly is now over US$ 1 billion, attacking crops such as tomatoes, melons, watermelons, cotton, bean and soybean, among others.
A study area was established at Embrapa - Genetic Resources and Biotechnology in order to collect indigenous natural enemies in B. tabaci (Biotype B) population. So far, Signiphora aleyrodis (Hymenoptera. Signiphoridae) and Nephaspis gemini (Coleoptera, Coccinellidae) have been found.
Prospection of Bemisia parasitoids was realized in other areas of Brazil. Strains of Encarsia formosa were found at the State of São Paulo, the State of Goiás and the Federal District (Brasília). The Brasilia strain of this parasitoid has been evaluated on the silverleaf whitefly populations and the results of parasitism found were: Lycopersicum esculentum cv. Salada, 90.75%, Lycopersicum esculentum cv. Nemadoro, 84, 25%, Brassica oleracea cv. Acephala, 19, 25% and Nicotiana tabacum cv. Turkish 45, 65%.
Investigator's Name(s): M. S. Palaniswami, Binu Antony, & Lisha Vijayan.
Affiliation & Location: Central Tuber Crops Research Institute, (ICAR), Trivandrum 695 017, INDIA.
Research & Implementation Area: Section D: Natural Enemy Ecology and Biological Control.
Dates Covered by the Report: 1997 - 1998
Survey and Identification of Bemisia tabaci Genn. and its Natural Enemies in India
Survey was conducted on the whitefly in various cassava and sweet potato growing areas, collected and maintained in the net house on cassava, tomato, sweetpotato and tobacco. Two biotypes were identified. Natural enemies include Scymnus sp. (Coccinellidae), Dipteran fly (unidentified), Encarsia flava (Aphelinidae) and pathogenic fungus. The field parasitisation of E. flava was found to range from 34 to 36%. E. flava prefers to oviposit on third, fourth and prepupal nymphs. Developmental period from egg to adult ranges from 13 to15 days. Biology, fecundity and longevity were studied. Pathogenicity tests of the fungus showed 50 to 55% pupal mortality. Population dynamics of host-parasitoid-pathogen ratio in the cassava field was in the range of 52:1.2:2 and it was at its peak during May. The ratio between whitefly population present on the lower leaf to middle and to upper leaf in a plant on an average was 1:1.2:1.4.
Investigator's Name(s): M. S. Palaniswami, Lisha Vijayan, & Binu Antony.
Affiliation & Location: Central Tuber Crops Research Institute (ICAR), Trivandrum 695 017, INDIA.
Research & Implementation: Section D: Natural Enemy Ecology and Biological Control.
Dates Covered by the Report: 1997 - 1998
Biology of Coccinellid Predators of Bemisia tabaci Genn.
During the survey three coccinellid predators were observed on Bemisia tabaci G. Among them Scymnus sp. is found to be a potential predator of the whitefly, a pest and vector of many viral diseases. The other two species of coccinellid predators were observed to be generalists whereas Scymnus sp. is found to be more of specific to Bemisia tabaci. The life history and behaviour of the Scymus sp. was studied in detail. The egg is white and newly emerged grubs are white. In one or two days the grub becomes yellow and subsequently the grubs are being covered with waxy coatings. Then the grubs are found to migrate from one leaf to another. Predation potential ranged from 36-40 %. The egg is transparent and slightly elongated measuring 0.35-0.40 mm in size, laid either singly or in pairs. The developmental duration of egg, larval and pupal stage was in the range of 5-6, 10-11 and 6-7 days. The larvae and the pupae are covered by waxy exudations a characteristic feature of Scymnus sp. It feeds on all stages of whitefly. Adult beetles are more voracious.
Investigator's Name(s): C. H. Pickett, G. S. Simmons1, & J. A. Goolsby2.
Affiliation & Location: California Department of Food & Agriculture, Biological Control Program, Sacramento, CA; 1USDA-APHIS PPMC, Brawley, CA; 2USDA-APHIS PPQ Mission, Texas.
Research & Implementation Area: Section D: Natural Enemy Ecology and Biological Control.
Dates Covered by the Report: February - May 1998
Augmentative Biological Control Using Transplants
Early season augmentative releases of Eretmocerus spp. (Hymenoptera: Aphelinidae) for control of silverleaf whitefly infesting spring planted melons in Imperial Valley can eliminate the need for late season applications of pyrethroids and other broad spectrum insecticides. This approach can enhance the regional population of highly effective whitefly parasites important to summer and fall field and vegetable crops. It may also promote the longevity of whitefly insecticides by reducing their usage. However, like other augmentative releases of natural enemies, use of Eretmocerus is currently expensive, possibly exceeding their short-term economic benefit. We report on a novel approach to enhancing early season field populations of Eretmocerus sp. using cantaloupe transplants. Cantaloupe seedlings prior to placement in fields are inoculated with a highly specific whitefly parasite, an Eretmocerus population recently imported from the United Arab Emirates. We want to determine whether control of whiteflies in fields receiving transplants inoculated with parasites, or "banker plants," is more effective than in fields receiving conventional hand releases. We hypothesize that parasites on transplants would be a more efficient means of introducing parasites because they would immediately be distributed throughout the entire field and have food readily available to them. Hand released parasites must first search for widely dispersed, low density prey, before parasitizing them. We also want to show that transplants with parasites can be integrated into imidacloprid treated fields at very little additional cost, or at least equal to conventional insecticide costs.
We completed our first field season this last spring. Parasites were released into two commercial farms of cantaloupe in the Imperial Valley. The first was an organic grower, where we compared the effect of banker plants (transplants with parasites) against plots receiving hand-releases of parasites, and a no-release control. Treatments were assigned to 1/3 ac plots using a randomized complete block design with 4 replicates. The second site was a conventional grower who uses imidacloprid (Admireâ), and we compared whitefly plant densities in 2 pairs of 1 acre plots with and without the addition of banker plants, respectively.
We succeeded in getting parasites onto banker plants and into fields at both the organic and conventional fields. About 10% of the melon plants in fields receiving banker plants were inoculated with parasites. However, we ended up releasing far fewer parasites using banker plants than we had planned; about 6400 to 7800 parasites per acre at the organic farm and approximately 24,000 per acre at the conventional field. This is much lower than our target of 40,000, the number found to give good control of whiteflies using conventional hand releases. Nevertheless, we measured significant differences in whitefly nymphal populations between the different treatment plots at the organic site. The lowest nymphal populations on the last two sample dates were recorded from the transplant plots, with increasing number in the hand release, and control plots. On 29 May 1998 banker plant plots averaged 0.13 nymphs/cm2 + 0.02 (95% CI) followed by hand release plots at 0.18 nymphs/cm2 + 0.04, and control plots 0.23 + 0.04 nymphs/cm2; and on 9 June 1998 bankers plant plots averaged 0.28 nymphs/cm2 + 0.06 followed by hand release plots at 0.41 nymphs/cm2 + 0.1, and control plots 0.51 + 0.1 nymphs/cm2. We detected few whiteflies at the conventional field receiving an imidacloprid treatment. Parasitism remained extremely low the entire season in both treatments, most likely as a result of a rare host population.
Investigator's Name(s): C. H. Pickett, G. S. Simmons1, and J. A. Goolsby2, & D. Overholt3.
Affiliation & Location: California Department of Food & Agriculture, Biological Control Program, Sacramento, CA; 1USDA-APHIS PPMC, Brawley, CA; 2USDA-APHIS PPQ Mission, Texas; 3 Pink Bollworm Program, CDFA, Visalia, CA.
Research & Implementation Area: Section D: Natural Enemy Ecology and Biological Control.
Dates Covered by the Report: August 1997 - November 1998
Fall Releases of Parasites into Citrus
The silverleaf whitefly (Bemisia argentifolii) is an increasingly important pest of cotton in the San Joaquin Valley. Field studies suggest that citrus has become an important overwintering site for this whitefly. Cotton has the highest incidence of whitefly infestations in areas of the Valley with a matrix of both citrus and cotton. We report on large scale releases of primarily Eretmocerus emiratus and secondarily E. mundus and E. hayati into three citrus groves. The study has two goals: (1) to determine if exotic parasites released into citrus during the fall will overwinter in this habitat and move into cotton the following spring; and (2) to permanently establish new populations of exotic parasites specific for the silverleaf whitefly.
Three study sites were identified, one each in Fresno, Tulare, and Kern Counties. Sites consisted of citrus and cotton acreage managed by the same owner. Cotton is grown directly adjacent to the citrus, and growers have had a history of silverleaf whitefly problems. They also use the new growth regulators (IGRs) for whitefly control. We began releasing parasites in early September when migrating whitefly nymphs were first recorded from citrus leaves. Over 100,000 parasites were released weekly at each location and a total of 4.05 million were released in 1997 and over 10 million in fall 1998. The dispersal of the released parasites was recorded using sticky cards with identification based on the adult males since they could be readily distinguished from native Eretmocerus while on the sticky cards.
The invading adult whitefly populations peaked in early September, 1997 and the egg population shortly thereafter (1998 data has yet to be summarized). Although about the same number of adult whiteflies were caught on sticky cards at the Kern and Tulare County sites, far more eggs and nymphs were recorded at the former. Most of the nymphs recorded from citrus leaves at all three sites were early, not late instars. The Fresno farm never developed substantial whitefly populations in their citrus. The number of whitefly nymphs successfully developing to adults were determined by the presence of an exit hole in the exuviae. At all three sites, the number of nymphal parasites that successfully emerged to adults was only a small fraction of the number of late nymphal instars, less than 1%. The maximum number of whitefly completing development (whitefly exit holes in exuviae) in citrus was recorded from the Kern County Site (0.016/cm2 leaf), with fewer at the other two sites. Preliminary data from a greenhouse study (one replicate) showed that only 19% of eggs matured to adults on citrus in the absence of parasites, with 4% surviving to adults in the presence of parasites. This study was conducted under optimal conditions—humid, warm. These results suggest only a very small fraction of the eggs oviposited by invading whiteflies actually developed to adults.
We began sampling weeds in January for the presence of whiteflies and parasites and that work is ongoing. We also began sampling cotton, but much later than anticipated, around May. Recoveries of exotic parasites this spring from weeds, sticky cards, and in cotton leaves adjacent to citrus shows that released parasites from at least one site moved into and attacked whitefly in adjacent cotton the following spring. We are continuing to sample cotton and citrus to determine which species of released parasites is dominate (80% of our releases were Eretmocerus emiratus, and 20% E. mundus and E. hayati) and to what extent they move into the cotton at all three sites.
Investigator's Name(s): Tadeusz J. Poprawski1 & Matthew A. Ciomperlik2.
Affiliation & Location: 1Joint Affiliation: Texas Agricultural Exp. Station and USDA-ARS, Beneficial Insects Research Unit, Weslaco, TX; and 2USDA-APHIS-PPQ Mission Plant Protection Center, Mission, TX.
Research & Implementation Area: Section D: Natural Enemy Ecology and Biological Control.
Dates Covered by the Report: Summer 1998
Impact of Beauveria bassiana on Natural Populations of Sweetpotato Whitefly Predators
Field applications of Beauveria bassiana (the oil-based mycoinsecticide Mycotrol® (ES) at the rate of 5 x 1013 conidia [AI]/ha for control of Bemisia argentifolii nymphs were made on 30 June and 7, 20 and 28 July 1998 in soybeans "Vernal' at Mission, TX. Samples of sweetpotato whitefly predators were collected from one 30-m section in the middle of each of 3 replicated plots (treated and untreated plots were 0.135 ha in size) using sweepnets, on 8, 21, 23 and 29 July, and 6 August to determine the impact of the fungus on predator numbers. In addition, predator samples taken from the treated and untreated plots were returned to the laboratory where they were retained to determine which species were affected by the fungus and mortality rates due to mycosis. Additional active predators were collected from the untreated plots. The activity of B. bassiana (strain GHA, the AI in the formulated Mycotrol ES) on these predators was assessed using one application rate in a series of 3 laboratory bioassays. The rate applied to the predators (number of conidia per mm2 of the Potter spray tower arena) was 6.25 lower than the field rate. A 0.01% aqueous Tween 80 carrier control was included with the fungal treatment. After treatment, test insects from the field samples retained in the laboratory and those from the bioassays, fed untreated whitefly nymphs ad libitum, were maintained in rearing cages for 10 days, at 25ºC and 50-55% RH under a photophase of 16:8 (L:D) h. Dead insects were removed daily from the cages, surface-sterilized in 0. 13% benzalkonium chloride, rinsed in sterile distilled water and finally plated on 2% agar supplemented with 0.5% gentamicin. The plates were incubated at 25ºC for 48 h and cadavers were scored for overt mycosis (sporulation).
Predator populations were well established within the soybean crop prior to and during B. bassiana applications. No significant differences in numbers of predators between the fungus-treated and the untreated plots were found at any given sampling date nor on a seasonal basis [t test on log (n + 1) transformation of the data] (Geocoris punctipes - all Ps >0.2; Scymnus loweii - all Ps >0.05; and others (Collops vittatus, Sinea diadema, Nabis americoferus, Zelus renardii, Notoxus monodon, Chrysoperla rugilabris, Hippodamia convergens, Coleomegilla maculata, unidentified coccinellids- all Ps >0.1).
In the retention study, there were generally, but not always, significant differences (chi-square test) in mortality attributable to B. bassiana between the predators collected from the fungus-treated plots and the untreated plots. Geocoris punctipes - 54. 1% mycosis in the Beauveria plots vs. 3.7% in the untreated plots (P <0.001) in the 8 July samples, 22.0 vs. 0.6% (21 July; P <0.001), 19.3 vs. 0% (29 July; P = 0.002); 28.6 vs. 0% (6 August; P = 0.155). Mycosis trends in S. loweii, N. americoferus, and several other predator species were similar to the above trends. Moreover, mycosis rates were probably understated because many predators killed by B. bassiana most likely fell to the ground and escaped collection.
Laboratory bioassays generally corroborated the retention study data. No control predator died from mycosis. The 10-d Abbott corrected percentages of mortality [mycosis], pooled over the 3 bioassays, in the fungal treatment were: G. punctipes - 49.3 [44.4]; S. loweii - 21.1 [2.1; and others (Z. renardii, C vittatus, S. diadema,, N. americoferus, C. rufilabris, unidentified damsel bugs and coccinelids, and unknown) - 48.4 [13.7] percent.
We conclude that field populations of nontarget beneficial insects are much more adversely affected by applications of B. bassiana than previously reported by several authors who drew their conclusions from population estimates made in situ.
Investigator's Name(s): W. J. Roltsch.
Affiliation & Location: California Department of Food & Agriculture, Biological Control Program, 4151 Hwy. 86, Brawley, CA 92227.
Research & Implementation Area: Section D: Natural Enemy Ecology and Biological Control.
Dates Covered by the Report: 1997 - 1998
Perennial Plant Refuges for Silverleaf Whitefly Natural Enemy Conservation in Imperial Valley, CA
Numerous perennial plant species have been screened in small plantings to determine their potential usefulness in conserving silverleaf whitefly parasitoids in the Imperial Valley environment, characterized by summer temperatures exceeding 40o C and highly alkaline soils. Several plant species that demonstrated potentially valuable whitefly/parasitoid relationships have been found to be poorly suited for environmental conditions. One of these is Lavatera thuringiaca (common name: lavatera). Several desert plant species continue to be of interest. These include, Tecoma stans (common name: yellow bells) and Justicia californica (common name: chuparosa). In addition, Alyogyne huegelii (common name: blue hibiscus) is a recently introduced ornamental from Australia, and often contains populations of heavily parasitized whitefly. This plant has only been under assessment for one year, therefore its tolerance to local soil conditions is not well known. During the past year, two perennial plant strips previously planted with lavatera, chuparosa and rue have been modified by the elimination of lavatera and the addition of yellow bells and a small number of blue hibiscus. In 1999, plants should be large enough to initiate sampling.
Investigator's Name(s): W. J. Roltsch1, G. S. Simmons2 & K. A. Hoelmer3.
Affiliation & Location: California Department of Food & Agriculture, Biological Control Program, 4151 Hwy. 86, Brawley, CA 92227 1, USDA-APHIS-PPQ, Western Region and Phoenix Plant Methods Center, Brawley, CA 92227 2 & USDA-ARS, EBCL, Parc Scientifique Agropolis II, Montelier, Cedex 5, France3 (formerly: USDA-APHIS, Phoenix Plant Protection Center, Brawley, CA).
Research & Implementation Area: Section D: Natural Enemy Ecology and Biological Control.
Dates Covered by the Report: 1997 to 1998
Establishment of Introduced Parasitoids of the Silverleaf Whitefly in Imperial Valley, CA
Since 1994, a number of exotic Eretmocerus and Encarsia species/populations have been evaluated in field cages, and released in commercial fields, refuge nursery plots and urban yards. The most promising Eretmocerus for this desert region include: Eretmocerus emiratus Zolnerowich & Rose, E. hayati Z. & R., E. mundus Mercet, and E. sp. from Ethiopia. To date, one population of Encarsia (E. transvena (Timberlake) from Pakistan) looks promising.
Parasitoid population development in un-inoculated refuge nursery plots for 1998: Four, one-half acre refuge nursery plots were monitored for exotic parasitoid activity. Each plot consisted of okra and basil during the warm season, and collard and sunflower during the cool season. These plots were not inoculated with exotic whitefly parasitoids during 1998 so that populations released in previous years at these sites could be assessed for their ability to overwinter and compete with native species. Overwintering on cole crops was confirmed albeit in low numbers. During the summer, population densities soared on okra, basil and adjacent cotton. Using traits associated with males to distinguish exotic Eretmocerus from the native E. eremicus, it was determined that by late August there was a greater proportion of exotic Eretmocerus (upwards of 80% on okra and cotton) than native Eretmocerus. This is particularly noteworthy, because these findings occurred at a time of year when the native Eretmocerus eremicus typically reaches high densities. The determination of which exotic Eretmocerus species dominated is pending, however, E. emiratus and E. mundus were common. Within these same plots, Encarsia transvena increased to very high densities as well. Based on DNA testing (RAPD-PCR by USDA-APHIS, Mission Biological Control Center, Mission, TX), all Encarsia transvena collected in these plots and at all other recovery sites since September of 1997 are those from Pakistan. Prior to the release of E. transvena from Pakistan, E. transvena from Spain were detected over a one year period (1996 - July of 1997) at several release locations. In contrast to the population from Pakistan, field cage tests and sample data from several locations have indicated that the population from Spain is not capable of rapid population increase during the summer months in Imperial Valley.
Regional surveys: During late summer and fall of 1998, exotic Eretmocerus and Encarsia transvena were collected from numerous ornamental plants in several communities in Imperial Valley, and at a number of conventionally managed cotton fields during early September. Data available to date regarding fall samples of ornamental plants at 15 urban sample sites in three communities indicate that exotic Eretmocerus were present in 10 of 15 sites. On average, 25% of the Eretmocerus at the 10 locations was exotic. Exotic Eretmocerus were detected in two of the eleven cotton field samples. Of these field samples, 6 sites had from 15 to 29 male specimens while 5 sites had from 30 to 66 male specimens. Within the two field sites where exotic Eretmocerus were detected, they represented 1-4% of the total Eretmocerus population. The locations where exotic Eretmocerus were found are remote from all 1998 release locations. In addition, Encarsia transvena were detected in one of the cotton fields located no closer than two miles from any known release site.
Summary: To date, it has been determined that several newly released parasitoid species have established in the Imperial Valley and are capable of extensive population increase. Survey data for 1998 indicate that these species are becoming widely distributed in urban areas and relatively common in agricultural fields as well.
Investigator's Name(s): W. J. Roltsch & J. A. Brown. \ Affiliation & Location: California Department of Food & Agriculture, Biological Control Program, 4151 Hwy. 86, Brawley, CA 92227 and California Department of Food & Agriculture, Biological Control Program, 3288 Meadowview Rd., Sacramento, CA 95832.
Research & Implementation Area: Section D: Natural Enemy Ecology and Biological Control.
Dates Covered by the Report: 1997 - 1998
Nursery Plots for Establishing Exotic Parasitoids of the Silverleaf Whitefly in Imperial Valley, CA
Field plots of approximately one-half acre are utilized for mass propagation of exotic parasitoid species to facilitate regional establishment. Each site is composed of one quarter acre of okra and one quarter acre of basil planted in March. Second through fourth instar whitefly nymphs are characteristically present on these plantings by early June. During late May through June, each field plot is inoculated with approximately 200,000 of one or a combination of exotic parasitoid species. The number of parasitoids emerging from these plants is very high by late August. Based on sample data consisting of counts of parasitoid pupae per leaf, number of leaves per plant and plants per 1200 row feet (approx. ¼ acre), it was estimated on 28 August 1998 that over one million Eretmocerus parasitoids were emerging on a daily basis from the okra plants alone. Furthermore, it was determined that 50% of these were exotic. Because of small leaf size and complex overall plant structure, the estimation of absolute densities of parasitoids on the basil plant component was not done. Typically, whitefly densities on basil are much lower than on okra in Imperial Valley, however, percent parasitism is very high. During 1998, parasitoid densities were sufficient to nearly eliminate whitefly densities, however, whitefly recruitment from adjacent areas continued to support densities of whiteflies in the plots. At one site, approximately 4,000 Encarsia transvena on potted collard plants were released. By 28 August there were over 84,000 adult wasps emerging per day on okra.
For two successive years, this method has been very useful for propagating large numbers of exotic parasitoids, from late summer through fall, to facilitate regional establishment. To be successful, it is important to have a very well maintained plot of okra and basil. Weedy plots or otherwise unthrifty plants are of little value.
Investigator's Name(s): Alvin M. Simmons1 & Gloria S. McCutcheon2.
Affiliation & Location: 1USDA-ARS, U.S. Vegetable Laboratory, Charleston, SC; 2CREC, Clemson University, Charleston, SC.
Research & Implementation Area: Section D: Natural Enemy Ecology and Biological Control.
Dates Covered by the Report: 1998
Attractancy of Crops to a Parasitoid of Bemisia and Daily Foraging
The influence of selected horticultural and agronomic plant species on attractiveness for foraging by Encarsia pergandiella Howard was determined. Greenhouse tests were conducted with seven diverse crops: cantaloupe, collard, cotton, cowpea, bell pepper, soybean, and tomato. Some of these, such as cantaloupe and cotton, are excellent hosts for Bemisia argentifolii, while others, such as cowpea and bell pepper, are substandard whitefly hosts. The tests were conducted on plants free of whitefly nymphs in an open greenhouse colony of indigenous E. pergandiella. In addition, greenhouse tests were conducted to determine incidence of daily foraging by this parasitoid. The parasitoid was most attracted to cowpea, followed by cotton. The fewest parasitoids were observed on collard. Attractance was based on the abundance of the parasitoids on the plants following their landing on the leaves. Leaf area was similar among plant types. Specific reasons for variable parasitoid foraging among the plant species may include a combination of factors such as plant semiochemicals, plant color, and plant texture.
The propensity of the parasitoid to forage on the lower leaf surface compared with the upper surface varied among crops (45-90% was on the lower leaf surface) and over time ( 50% was on the lower leaf surface around sunrise while 90% was on the lower surface by mid-day). Overall foraging was low around sunrise and sunset, but peaked near solar noon.
Results from this study have implications on parasitoid conservation, and host plant resistance.
|