Egg loads and egg masses: Parasitism ofChoristoneura rosaceana eggs by Trichogramma minutum after inundativerelease in a commercial blueberry field

Inundative releases of Trichogramma minutum Riley were made in a commercialblueberry field in British Columbia, Canada, todetermine the extent of dispersal of adult wasps, andto determine whether complete parasitism of eggswithin egg masses of the target host [oblique-bandedleafroller (OBLR), Choristoneura rosaceana(Harris)] occurred. Three weekly releases of waspswere made from a single release point in the center ofeach field during the flight of first generation OBLRadults. Sticky trap, sentinel egg mass andtarget-host egg mass data all indicated only a limitedrange of dispersal of T. minutum within thefield. In addition, only partial parasitism of eggmasses of the target host occurred even in closeproximity to the release point. We discuss theimportance of determining the response of Trichogramma females to previously-parasitized eggswhen using Trichogramma wasps for biologicalcontrol of lepidopterous species that oviposit largeegg masses.     

The scale response ofTrichogramma [Hymenoptera: Trichogrammatidae]: Variation among species in host specificity and the effect of conditioning

Host specificity and the effect of conditioning on a behavioral response to lepidopteran scales varied among the females of 4Trichogramma spp. observed in laboratory experiments.Trichogramma species nrPretiosum Riley andT. exiguum Pinto & Platner responded weakly toOstrinia nubilalis (Hübner) scales relative toHeliothis zea (Boddie) andManduca sexta (L.).T. maltbyi Nagaraja & Nagarkatti andT. minutum Riley did not discriminate between scales from these 3 hosts. Conditioning with various combinations of host scales and eggs did not alter host specificity, but in some cases, changed general responsiveness to scales. These were attributed to habituation, loss of appetitive drive due to long oviposition bouts, and associative learning. In general, the scale response seems to be innate and fairly nonspecific.      

The relationship between egg load and fecundity among Trichogramma parasitoids

1. The relationships between parasitoid egg load, size, and age (3–72 h) for Trichogramma minutum, T. platneri, and T. pretiosum, reared from two factitious hosts, Ephestia kuehniella and Sitotroga cerealella, were evaluated to test the hypothesis that 24‐h egg load can be used to estimate the fecundity of Trichogramma parasitoids. 2. Egg load increased in relation to female age over the first 3 days of adult life for all three Trichogramma species to a mean egg storage capacity of 46.7 eggs for T. minutum, 41.1 for T. pretiosum, and 35.7 for T. platneri. At 24 h of age, T. minutum had matured enough eggs to fill 67% of its storage capacity, in comparison with 74% for T. pretiosum and 91% for T. platneri. There was a positive relationship between egg load and parasitoid size for all ages of the three Trichogramma species reared from both hosts (with the exception of T. platneri at 3 h post emergence), accounting for 14–69% of the variance in egg load. 3. The potential fecundity, realised (3 day cumulative) fecundity, and oviposition rate (potential fecundity/longevity) of T. platneri were all related linearly to size‐dependent variation in 24‐h egg load, but only the realised fecundity of T. pretiosum, and none of the reproductive characteristics of T. minutum. It is suggested that 24‐h egg load may not be an accurate measure of egg storage capacity in parasitoids and should be used cautiously to represent fecundity. 4. The potential fecundity of seven Trichogramma species reared from E. kuehniella varied from 55 to 150, but neither potential fecundity nor oviposition rate was related significantly to egg load (represented by eggs laid during first 24 h). Selection to avoid egg depletion in the attack of gregarious hosts appears most likely to account for the variation in potential fecundity among Trichogramma species.     

Quality assessment of three species of commercially produced Trichogramma and the first report of thelytoky in commercially produced Trichogramma

Weekly shipments of Trichogramma pretiosum Riley, Trichogramma minutum Riley, and Trichogramma brassicae (Bezdenko) (Hymenoptera: Trichogrammatidae) from a single insectary were assessed to determine whether survivorship with and without honey, emergence rate, and sex ratio were consistent over a five-week period in 2000. At least one shipment was misidentified by the insectary. Emergence rates were over 75% in 15 out of 17 shipments, although emergence varied significantly over the experimental period for each species. Mean longevity of honey-fed individuals was 7.16 days for T. pretiosum, 6.71 days for T. minutum, and 4.02 days for T. brassicae; mean longevity of unfed individuals was 2.68 days, 2.42 days, and 1.96 days, respectively. Mean sex ratios (proportion of individuals that were male) were 0.029 for T. pretiosum, 0.465 for T. minutum, and 0.444 for T. brassicae. Seventeen out of 18 virgin T. pretiosum females produced daughters, and three out of a subset of six of these females produced sons after being fed the antibiotic tetracycline. These results are consistent with infection by a parthenogenesis-inducing strain of Wolbachia.     

Efficiency of different egg parasitoids and increased floral diversity for the biological control of noctuid pests

Augmentative biological control of insects is a tool of Integrated Pest Management programs. In many agroecosystems, biological control is exercised largely by parasitoids, and it is found that the presence of food resources, as provided by flowering plants, can have a positive effect on survival, search ability and parasitism rate of parasitoid species. In Colombia, a recently established export crop, the cape gooseberry, is under continuous attack by a Lepidopteran species complex in the family Noctuidae. Our first objective was to test the longevity and parasitism rates of three species of egg parasitoids in the genus Trichogramma (Trichogramma atopovirilia Oatman & Platner, Trichogramma exiguum Pinto & Platner, and Trichogramma pretiosum Riley) for Spodoptera frugiperda Smith and Copitarsia decolora Gueené. Our results suggest that T. atopovirilia and T. pretiosum could be promising parasitoids for the control of S. frugiperda and C. decolora, with a percentage parasitism of between 30% and 60%, respectively. For our second objective, we selected T. atopovirilia as a model species to evaluate the effect of the presence of flowering plants on the longevity and parasitism rate in both, no choice and multiple choice experiments, under laboratory and field conditions. Our results consistently showed that the presence of red clover (Trifolium pratense L.) can increase the longevity and parasitism rate of T. atopovirilia, suggesting that providing food resources to parasitoids in cape gooseberry fields should be part of a habitat diversification strategy to control noctuid pests.     

Malic enzyme,phosphoglucomutase and phosphoglucose isomerase isozymes inTrichogramma [Hym.: Trichogrammatidae]

ME, PGM and PGI electrophoretic banding patterns in 20 laboratory cultures representing 14 species ofTrichogramma were studied. Variations in PGM were found inT. exiguum, T. marylandense, andT. pretiosum. PGI also showed variation inT. exiguum, T. marylandense, T. minutum, andT. parkeri. However, ME variations were found only inT. pretiosum. Based on progeny analyses, we concluded that ME is a tetramer inTrichogramma with fast and slow alleles at a single locus, and that both PGM and PGI have a single locus and each has four alleles. PGM is a monomer, but PGI is a dimer.

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Résumé Les bandes électrophorétiques de l'enzyme malique, de la P.G.M. et de la P.G.I. ont été étudiées chez 20 souches de laboratoire représentant 14 espèces deTrichogramma. Des variations de la P.G.M. ont été trouvées chezT. exiguum, T. marylandense etT. pretiosum. La. P.G.I. montre aussi des variations chezT. exiguum, T. marylandense, T. minutum etT. parkeri. Par contre, des variations de l'enzyme malique ne sont trouvées que chezT. pretiosum. En nous basant, sur l'analyse de progénitures, nous avons conclu que l'enzyme malique est un tétramère chezTrichogramma comprenant un allèle “lent” et un alléle “rapide”, à un seul locus, et que la P.G.M. et la P.G.I. ont chacune un seul locus à quatre allèles. La P.G.M. est un monomère mais la P.G.I. est un dimère.

     

Trichogramma egg parasitism ofHelicoverpa armigera on short-duration pigeonpea intercultured with sorghum

The levels of egg parasitism byTrichogramma spp. (Hymenoptera: Trichogrammatidae) on populations ofHelicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) were recorded on sorghum (Sorghum bicolor L.) and on two flushes of flowers on short-duration pigeonpea (Cajanus cajan L.).H. armigera oviposition was concentrated on the early flowering stage of sorghum and the flowering and early podding stages of both flushes of pigeonpea. Parasitism on sorghum increased rapidly as egg density increased and reached a peak of 74.6%. Parasitism on pigeonpea was concentrated onH. armigera eggs laid on the first flush of pigeonpea flowers with a maximum of 69.2%. These high levels of parasitism on pigeonpea coincided with the period of parasite activity on sorghum. The levels of parasitism then declined rapidly and only very low levels were detected on a second flush of flowers. This rapid decline resulted in the overall egg mortality caused byTrichogramma on pigeonpea to be low, with a maximum of 7.8% caused by parasitism, compared to 34.4% on sorghum. The pattern of parasitism suggests that a transfer of parasites occurred from sorghum to pigeonpea. The rapid decline of parasitism on the pigeonpea indicates that parasite populations cannot be sustained on pigeonpea once the influx from sorghum stops. The results are discussed in terms of a possible method of encouraging the transfer of parasites from sorghum to short-duration pigeonpea by producing a more continuous cropping environment.     

Effect of induced tolerance to Bt toxin on the egg size of Helicoverpa armigera and parasitism by Trichogramma pretiosum

Larvae of Helicoverpa armigera (Hübner) can develop a form of Bt tolerance after exposure to sub‐lethal doses of Bt‐toxin subclass Cry1Ac. Increasing levels of tolerance are produced over generations of larval exposure, which are not related to DNA sequence changes, and are largely maternally transmitted. The characteristic of maternal transmission, combined with the importance of egg parasitoids to cotton pest management, raises questions about the effects of Bt tolerance/exposure on the eggs of H. armigera and on some key metrics of egg parasitism. In the present study, the effect of inducible tolerance on eggs of H. armigera and parasitism by Trichogramma pretiosum (Riley) is investigated. First, the volumes of eggs laid by susceptible and tolerant H. armigera females are compared. In addition, the effect of inducible tolerance on egg parasitism is determined by comparing parasitism success, the number of adult wasps emerged per host egg, and the proportion of male and female offspring emerged per host egg. The results obtained suggest that Cry1Ac‐tolerance is associated with increased egg volume, even after just one generation of sub‐lethal exposure. When tolerant H. armigera are freed from ongoing sub‐lethal exposure, a corresponding decrease in egg volume is not detected. Although there is no difference in the percentage of eggs parasitized, there is an increase in the number of emergent parasitoids, especially males, from eggs laid by tolerant H. armigera. These results confirm that maternally‐transmitted Bt tolerance is reflected in the phenotype of the eggs of tolerant offspring, which affects egg parasitism.     

Temperature-Dependent Parasitism,Survival, and Longevity of Five Species of Trichogramma Westwood (Hymenoptera: Trichogrammatidae) Associated with Anticarsia gemmatalis Hübner (Lepidoptera: Noctuidae)

Egg parasitoids of the genus Trichogramma Westwood play an important role in the control of the velvetbean caterpillar Anticarisa gemmatalis Hübner in soybean crops in Southern Brazil. The effectiveness of Trichogramma species as biocontrol agents is dependent of several factors, but their adaptation to the climatic conditions of the region where they will be released is one of the most important. In this context, this study evaluated the effects of five constant temperatures ranging from 14 to 30°C on parasitism, age-specific survival, progeny production and longevity of Trichogramma pretiosum Riley, Trichogramma atopovirilia Oatman & Platner, Trichogramma acacioi Brun, Moraes & Soares, Trichogramma lasallei Pinto, and Trichogramma rojasi Nagaraja & Nagarkatti. We demonstrate that temperature differently affected the species of Trichogramma investigated when using eggs of the velvetbean caterpillar. We also demonstrate that T. pretiosum and T. atopovirilia are better adapted to a wide range of temperatures than the other species evaluated, and are therefore better suited as biocontrol agents for applied biological control programs of A. gemmatalis.     

The Effectiveness of Trichogramma chilonis,Trichogramma pretiosum and Trichogramma brasiliense (Hymenoptera: Trichogrammatidae) as Parasitoids of Helicoverpa armigera (Lepidoptera: Noctuidae) on Sunflower (Helianthus annuus) and Redgram (Cajanus cajan)

The performance of three species of trichogrammatids on the pest, Helicoverpa armigera was evaluated in the laboratory and screenhouse conditions in Karnataka, India during 1996-97. Laboratory studies indicated that Trichogramma chilonis and Trichogramma pretiosum were more effective parasitoids of H. armigera than Trichogramma brasiliense. In screenhouse conditions, T. chilonis was the most effective parasitoid of H. armigera eggs on sunflower plants in comparison to the other two trichogrammatid species. When releasing 50?000 per ha on sunflower and redgram, T. chilonis parasitised 50.1 and 11.4% H. armigera eggs, respectively. The position of H. armigera eggs on different plant parts of sunflower had no effect on parasitism by T. chilonis. However, parasitism by the same trichogrammatid among different plant parts of redgram varied significantly. It parasitized 43.4 and 18.7% H. armigera eggs on leaves and flowers, respectively, and significantly fewer, 3.9%, on pods (P<0.05). The growth stage of redgram plants also had an effect on parasitism by T. chilonis, parasitism being extremely low on plants with pods.     

Assessment ofTrichogramma species for biological control of forest lepidopteran defoliators

In a laboratory study, we determined the potential of threeTrichogramma (Hymenoptera: Trichogrammatidae) species,T. brassicae Bezdenko,T. minutum Riley andT. nr.sibiricum Sorokina, for biological control against six species of forest lepidopteran pests, black army cutworm, hemlock looper, eastern spruce budworm, western spruce budworm, white-marked tussock moth, and gypsy moth. Females of each parasitoid species were offered eggs from each of the six host species. Parasitization and the effect of the host species on the emerging progeny were examined and recorded.Trichogramma minutum had the broadest host range and successfully parasitized four host species out of the six offered.Trichogramma nr.sibiricum had the narrowest host range and parasitized only two species of hosts. Of the six host species, black army cutworm was the most preferred by all threeTrichogramma species; white-marked tussock moth and gypsy moth were not parasitized by any parasitoids. There was a positive correlation between the size of female offspring and their corresponding egg complement in all three parasitoid species. The developmental time of parasitoids from egg to adult was influenced by both the parasitoid and host species. Our results suggest thatT. minutum has the greatest potential for biological control against various forest lepidopteran pests and that the black army cutworm may be the best target candidate for further study.     

IndigenousTrichogramma (Hym.: Trichogrammatidae) parasitizing eggs ofRhopobota naevana (Lep.: Tortricidae) on cranberries in British Columbia

Two indigenous species ofTrichogramma were reared from natural populations of the blackheaded fireworm,Rhopobota naevana (Hübner) infesting cranberries in British Columbia, Canada. One was identified asTrichogramma sp. nr.sibericum Sorokina and the other wasTrichogramma minutum Riley. Percentage of parasitized hosts increased during the season in an abandoned field, but decreased in a commercial field where pesticides were used. The potential ofTrichogramma as a biological control agent against the fireworm is discussed.     

Development of a continuous cell line from the insect egg parasitoid,Trichogramma pretiosum (Hymenoptera; Trichogrammatidae)

Summary A cell line (IPLB-TpE1) was established from embryos of the hymenopteran parasitoid,Trichogramma pretiosum Riley. Cultures contain a mixture of attached, elongate spindle-shaped cells and large aggregates of suspended cells. Chromosomes of the cells were typical ofTrichogramma species and isozyme characterization showed patterns similar toT. pretiosum adults, but distinctly different fromHeliothis zea, the lepidopteran host from which parasite eggs were obtained. The cells are capable of growth over a wide range of osmotic pressures with equal growth between 350 and 600 mOsm/kg. Optimal growth was obtained with a pH of 6.5. Doubling time at the 40th passage was 72 h and cultures are currently subcultured at weekly intervals. The mention of a commercial product does not constitute an endorsement by the U. S. Department of Agriculture.     

Parasitism of cotton leafworm Alabama argillacea eggs by Trichogramma pretiosum in commercial cotton fields

Release of natural enemies in commercial fields is challenging and has been inconsistent in the results achieved. This work discusses the augmentative releases of Trichogramma pretiosum to control the cotton leafworm (CLW) Alabama argillacea and also examines the parasitoid–host interaction under grower field conditions. The treatments consisted of fields with and without releases of T. pretiosum set up in Primavera do Leste and Campo Verde Counties, MT, Brazil, during three different seasons (2003 and 2004 dry and 2004 regular summer seasons). Trichogramma wasps were weekly released in the treated fields throughout the entire sampling period (14–15 week period) at a rate of 100 000 wasps per hectare. One‐way repeated measures analysis of variance was performed for the number of parasitized eggs, followed by a meta‐analysis procedure to determine the contribution of T. pretiosum release on overall parasitism. In addition, regression analysis was conducted with each season’s data sets to study the relationship of the host density and parasitism response by T. pretiosum. The overall results of Trichogramma augmentative releases did not result in significant increase of CLW egg parasitism beyond the natural parasitism in the areas studied. However, based on Cohen’s d effect sizes from the meta‐analysis, the parasitism rate was greater in fields under T. pretiosum releases during four out of 15 weeks surveyed. The parasitism of CLW eggs by T. pretiosum exhibited host density‐dependence only in one out of three seasons surveyed. These findings are encouraging as they are evidence that T. pretiosum is able to maintain a considerable level of parasitism under commercial field conditions, highlighting their potential value in large‐scale commercial areas of cotton as previously found at the small and diverse farming scale. Future studies should address the potential of early‐season, low density releases of the parasitoid.     

The effect of host size on quality attributes of the egg parasitoid,Trichogramma pretiosum

In a study of the quality ofTrichogramma pretiosum Riley (Hymenoptera: Trichogrammidae), we compared female wasps emerging from natural hosts, parasitized in the laboratory or the field with those emerging from factitious hosts used for commercial mass production. Females from the natural hosts were larger, more fecund, and longer lived than those from the factitious hosts. Compared to small females, large female wasps are substantially more fecund when honey (carbohydrate) is available but marginally more fecund when honey is unavailable. The size of a femaleT. pretiosum depends on two factors: the size of the host egg from which it emerges even when the wasp was gregarious, and the number of conspecifics that emerge with it. The similarities in the size distribution of female wasps emerging from natural hosts, in conjunction with the mechanism by whichTrichogramma measure host size and allocate eggs accordingly, suggests the hypothesis that size related components of fitness in femaleT. pretiosum are under strong selection in the field.     

Two new species ofTrichogramma [Hym.: Trichogrammatidae] from the U.S.A.

Two new species ofTrichogramma from the U.S.A. are described.T. parkeri sp. n., a morphologically distinct species, was reared from an egg ofHeliothis zea (Boddie), whileT. platneri sp. n. which is morphologically indistinguishable fromT. minutum Riley, was reared from eggs ofCydia pomonella (L.). Reproductive incompatibility ofT. platneri andT. minutum is discussed.     

Searching Speed of Trichogramma minutum and Its Potential as a Measure of Parasitoid Quality

Searching speed has been proposed as a quality criterion for the prediction of field efficacy of mass-reared Trichogramma spp. The searching speed, walking speed, and activity of female T. minutum Riley were measured using an automated video tracking system. Two- and 3-day-old thelytokous females searched twice as fast as 1-day-old females, whereas the searching speed of a strain of arrhenotokous females was similar at all ages. When reared on Actebia fennica Tauscher, the resulting wide variation in wasp size was not related to searching speed or walking speed. Both strains of T. minutum searched faster later in the day. In a second laboratory experiment, the proportion of hosts parasitized, the proportion of hosts accepted, and searching speeds of parasitoids were measured simultaneously for groups of females of both strains. Percentage parasitism was related to host acceptance but not searching speed. Searching speed was unrelated to the estimated number of host contacts. These results suggest that searching speed is not a useful measure of parasitoid efficacy for T. minutum.     

Effects of fine-grain habitat complexity on egg parasitism by three species of Trichogramma

Effects of microhabitat complexity on host foraging by three species of Trichogramma (T. deion, T. ostriniae, and T. pretiosum) were evaluated under simulated stored product conditions. All three species have been considered as potential biological control agents for the Indianmeal moth, Plodia interpunctella, in retail stores and warehouses. Trials were conducted with single naïve female parasitoids in 10-cm Petri dishes that were either empty, contained flour, or contained millet. Empty 15-cm Petri dishes, which served as a surface area control, comprised a fourth treatment. Females were allowed to forage for sentinel egg disks for 2 h, after which percentages of parasitism and egg mortality were computed. In addition, behavioral observations were made on a subset of the trials. Trichogramma deion parasitized more eggs than the other two species in the empty dishes and in the dish containing flour. For T. deion, rates of parasitism and egg mortality were significantly greater in both the small and large empty dishes than in the small dishes containing flour or millet. Parasitism was consistently low for all three species in the grain-filled dishes. Among species, T. ostriniae spent the most time walking, while T. pretiosum was the most sedentary. In addition, T. pretiosum spent significantly more time on the first egg visited compared with subsequent eggs. T. deion may be the best-suited for use as a biological control agent for P. interpunctella. However, the potential negative effects of fine-grain habitat complexity should be taken into account when developing a release protocol for Trichogramma spp.     

The Oak-silkworm Egg Antheraea pernyi (Lepidoptera: Anthelidae) as a Mass Rearing Host for Parasitoids of the Genus Trichogramma (Hymenoptera: Trichogrammatidae)

The acceptance of 40 different strains of 24 Trichogramma (Hymenoptera: Trichogrammatidae) species for oak-silkworm host eggs, Antheraea pernyi Guerin-Meneville (Lepidoptera: Anthelidae) was tested in laboratory experiments. The oak-silkworm, which is commercially used in China to mass produce Trichogramma dendrolimi Matsumura on a large scale, was accepted for egg laying by 10 out of the 24 species tested but only 3 species (four strains of T. dendrolimi, three strains of T. chilonis Ishii and one strain of T. cacoeciae Marchal) successfully completed development to adult emergence. The number of adults emerged per host egg averaged 83.2, 37.0, 42.3, 53.0 for four different strains of T. dendrolimi; 42.5, 10.0 for two strains of T. chilonis; 24.5 and 0 for two strains of T. cacoeciae.

Seven other Trichogramma species develoedp in A. pernyi eggs, but no adult emergence occurred and no emergence holes on the chorion were found. The number of Trichogramma larvae, pupae, and adults together per host egg averaged 81.7 and 67.4 for two strains of T. embryophagum Hartig; 39.0 for T. japonicum Ashmead; 35.0, 16.7, 19.0, 0 for four strains of T. evanescens Westwood; 18.7, 0, 0, 0 for four strains of T. brassicae Bezdenko; 11.5 for T. piceum Dyurich; 76.4 and 23.0 for two unidentified strains collected in apple and vine orchards in Germany, respectively.

The following 14 Trichogramma species did not parasitize any A. pernyi eggs: T. atopovirilia Oatman & Platner, T. bourarachae Pintureau & Babault, T. buesi Voegél, T. funiculatum Carver, T. ivelae Pang & Chen, T. meyeri Sorokina, T. minutum Riley, T. nerudai Pintureau, T. nubilale Ertle & Davis, T. ostriniae Pang & Chen, T. principium Sugonjaev & Sorokina, T. pretiosum Riley and two further unidentified strains that originated from France and Switzerland.

The results confirmed that A. pernyi is a suitable host for rearing T. dendrolimi and T. chilonis and that the two species T. cacoeciae and T. embryophagum, under optimal conditions, might be possible candidates for rearing.     

A high incidence of parasitism ofHeliothis SPP. [Lep.: Noctuidae] larvae in cotton in Southeastern Arkansas

During 1981 and 1982, bollworm,Heliothis zea (Boddie), and tobacco budworm,H. virescens (F.), larvae (n=3,666) were collected from 41 cotton fields near Portland, Arkansas (USA) to assess the occurrence of parasitism. Three strategies were employed to controlHeliothis spp. in these fields: (1) release ofTrichogramma pretiosum Riley; (2) insecticidal control; or (3) inaction (check). Insecticide use in nonchemical control fields was reduced, but not eliminated.Heliothis spp. larvae collected in cotton had higher parasitism rates in 1981 (30.9%) and 1982 (50.1%) than had been reported for cotton since the advent of organochlorine insecticide usage. Four species of larval parasites and 1 species of larval-pupal parasite were recorded. The larval parasiteMicroplitis croceipes (Cresson) comprised 90.6% and 94.5% of all parasitic insects reared from field collectedHeliothis spp. in 1981 and 1982, respectively. No difference (P>0.05) in level of parasitism existed betweenH. zea andH. virescens. Differences between treatments occurred only in 1982 whenH. zea larvae were parasitized at a greater (P<0.05) rate in check fields (68.3%) than in insecticidal control fields (44.3%). Higher levels of larval parasitism in cotton fields may be a consequence of reduced insecticide usage and changes in materials applied, particularly the pyrethroids. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Dept. of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.