The potential of using artificial intelligence to improve skin cancer diagnoses in Hawai'i's multiethnic population

Skin cancer remains the most commonly diagnosed cancer in the USA with more than 1 million new cases each year. Melanomas account for about 1% of all skin cancers and most skin cancer deaths. Multiethnic individuals whose skin is pigmented underestimate their risk for skin cancers and melanomas and may delay seeking a diagnosis. The use of artificial intelligence may help improve the diagnostic precision of dermatologists/physicians to identify malignant lesions. To validate our artificial intelligence's efficiency in distinguishing between images, we utilized 50 images obtained from our International Skin Imaging Collaboration dataset (n = 25) and pathologically confirmed lesions (n = 25). We compared the ability of our artificial intelligence to visually diagnose these 50 skin cancer lesions with a panel of three dermatologists. The artificial intelligence model better differentiated between melanoma vs. nonmelanoma with an area under the curve of 0.948. The three-panel member dermatologists correctly diagnosed a similar number of images (n = 35) as the artificial intelligence program (n = 34). Fleiss' kappa (ĸ) score for the raters and artificial intelligence indicated fair (0.247) agreement. However, the combined result of the dermatologists panel with the artificial intelligence assessments correctly identified 100% of the images from the test data set. Our artificial intelligence platform was able to utilize visual images to discriminate melanoma from nonmelanoma, using de-identified images. The combined results of the artificial intelligence with those of the dermatologists support the use of artificial intelligence as an efficient lesion assessment strategy to reduce time and expense in diagnoses to reduce delays in treatment.

Petrifilm™ Rapid S. aureus Count Plate Method for Rapid Enumeration of Staphylococcus aureus in Selected Foods: Collaborative Study

A rehydratable dry-film plating method for Staphylococcus aureusin foods, the 3M™ Petrifilm™ Rapid S. aureus Count Plate method, was compared with AOAC® Official MethodSM 975.55 (Staphylococcus aureus in Foods). Nine foods—instant nonfat dried milk, dry seasoned vegetable coating, frozen hash browns, frozen cooked chicken patty, frozen ground raw pork, shredded cheddar cheese, fresh green beans, pasta filled with beef and cheese, and egg custard—were analyzed for S. aureus by 13 collaborating laboratories. For each food tested, the collaborators received 8 blind test samples consisting of a control sample and 3 levels of inoculated test sample, each in duplicate. The mean log counts for the methods were comparable for pasta filled with beef and cheese; frozen hash browns; cooked chicken patty; egg custard; frozen ground raw pork; and instant nonfat dried milk. The repeatability and reproducibility variances of the Petrifilm Rapid S. aureus Count Plate method were similar to those of the standard method.

Adapting a Skin Cancer Prevention Intervention for Multiethnic Adolescents

OBJECTIVE

We tested the effectiveness of a school-based skin cancer prevention intervention entitled "SunSafe in the Middle School Years" adapted for multiethnic high school students.

METHODS

In Hawai'i, 208 10th graders (51.6% Asian, 30.4% Native Hawaiian/Pacific Islander, 8.4% white, 3.5% Hispanic, 2.7% black) participated. Changes in sun protection knowledge, attitudes, and self-reported behaviors were measured using a standardized 18-item survey. The Systematic Observation of Sun Protection Factors (SOSPF) instrument assessed aggregate sun protection behaviors.

RESULTS

At posttest, improvements were found in 13 of 18 survey items (p < .05), and retained in 10 items at 12-months following baseline assessments; sun-protection attitudes and intended tanning behavior did not show improvement. Six observers using SOSPF reliably measured students' sun protection behaviors at school including use of hats, sunglasses, long sleeves, lower body coverage, and shade (ICC > .77).

CONCLUSIONS

We uncovered a lack of knowledge about UVR exposure, tanning, and lifetime skin cancer risk among multiethnic high school students. We found that students' tanning attitudes may be influenced by self-perceptions regarding their own complexion, but were willing to modify their sun protection behaviors once informed about skin cancer risk.

Novel colon cancer susceptibility variants identified from a genome-wide association study in African Americans

Genome-wide association studies (GWAS) in ethnic/racial minority populations can help to fine-map previously identified risk regions or discover new risk loci because of the genetic diversity in these populations. We conducted a GWAS of colorectal cancer (CRC) in 6,597 African Americans (1,894 cases and 4,703 controls) (Stage 1) and followed up the most promising markers in a replication set of 2,041 participants of African descent (891 cases and 1,150 controls) (Stage 2). We identified a novel variant, rs56848936 in the gene SYMPK at 19q13.3, associated with colon cancer risk (odds ratio 0.61 for the risk allele G, p = 2.4 × 10^-8 ). The frequency of the G allele was 0.06 in African Americans, compared to <0.01 in Europeans, Asians and Amerindians in the 1000 Genomes project. In addition, a variant previously identified through fine-mapping in this GWAS in the region 19q13.1, rs7252505, was confirmed to be more strongly associated with CRC in the African American replication set than the variant originally reported in Europeans (rs10411210). The association between rs7252505 and CRC was of borderline significance (p = 0.05) in a Hispanic population GWAS with 1,611 CRC cases and 4,330 controls. With the three datasets combined, the odds ratio was 0.84 for the risk allele A (95% confidence interval 0.79-0.89, p = 3.7 × 10^-8 ). This study further highlights the importance of conducting GWAS studies in diverse ancestry populations.

Risk of extracolonic cancers for people with biallelic and monoallelic mutations in MUTYH

Germline mutations in the DNA base excision repair gene MUTYH are known to increase a carrier's risk of colorectal cancer. However, the risks of other (extracolonic) cancers for MUTYH mutation carriers are not well defined. We identified 266 probands (91% Caucasians) with a MUTYH mutation (41 biallelic and 225 monoallelic) from the Colon Cancer Family Registry. Mutation status, sex, age and histories of cancer from their 1,903 first- and 3,255 second-degree relatives were analyzed using modified segregation analysis conditioned on the ascertainment criteria. Compared with incidences for the general population, hazard ratios (HRs) (95% confidence intervals [CIs]) for biallelic MUTYH mutation carriers were: urinary bladder cancer 19 (3.7-97) and ovarian cancer 17 (2.4-115). The HRs (95% CI) for monoallelic MUTYH mutation carriers were: gastric cancer 9.3 (6.7-13); hepatobiliary cancer 4.5 (2.7-7.5); endometrial cancer 2.1 (1.1-3.9) and breast cancer 1.4 (1.0-2.0). There was no evidence for an increased risk of cancers at the other sites examined (brain, pancreas, kidney or prostate). Based on the USA population incidences, the estimated cumulative risks (95% CI) to age 70 years for biallelic mutation carriers were: bladder cancer 25% (5-77%) for males and 8% (2-33%) for females and ovarian cancer 14% (2-65%). The cumulative risks (95% CI) for monoallelic mutation carriers were: gastric cancer 5% (4-7%) for males and 2.3% (1.7-3.3%) for females; hepatobiliary cancer 3% (2-5%) for males and 1.4% (0.8-2.3%) for females; endometrial cancer 3% (2%-6%) and breast cancer 11% (8-16%). These unbiased estimates of both relative and absolute risks of extracolonic cancers for people, mostly Caucasians, with MUTYH mutations will be important for their clinical management.

Risk of colorectal cancer for people with a mutation in both a MUTYH and a DNA mismatch repair gene

The base excision repair protein, MUTYH, functionally interacts with the DNA mismatch repair (MMR) system. As genetic testing moves from testing one gene at a time, to gene panel and whole exome next generation sequencing approaches, understandin g the risk associated with co-existence of germline mutations in these genes will be important for clinical interpretation and management. From the Colon Cancer Family Registry, we identified 10 carriers who had both a MUTYH mutation (6 with c.1187G>A p.(Gly396Asp), 3 with c.821G>A p.(Arg274Gln), and 1 with c.536A>G p.(Tyr179Cys)) and a MMR gene mutation (3 in MLH1, 6 in MSH2, and 1 in PMS2), 375 carriers of a single (monoallelic) MUTYH mutation alone, and 469 carriers of a MMR gene mutation alone. Of the 10 carriers of both gene mutations, 8 were diagnosed with colorectal cancer. Using a weighted cohort analysis, we estimated that risk of colorectal cancer for carriers of both a MUTYH and a MMR gene mutation was substantially higher than that for carriers of a MUTYH mutation alone [hazard ratio (HR) 21.5, 95% confidence interval (CI) 9.19-50.1; p < 0.001], but not different from that for carriers of a MMR gene mutation alone (HR 1.94, 95% CI 0.63-5.99; p = 0.25). Within the limited power of this study, there was no evidence that a monoallelic MUTYH gene mutation confers additional risk of colorectal cancer for carriers of a MMR gene mutation alone. Our finding suggests MUTYH mutation testing in MMR gene mutation carriers is not clinically informative.

Abstract B56: Adapting SunSafe: A skin cancer prevention intervention for use with multiethnic high school students

Skin cancers are one of the most preventable types of cancer. However, since 2004, skin cancer incidence rates have increased 3% each year in the U.S. In 2015, more than 3 million Americans will develop skin cancer and 76,000 will need treatment for the most deadly form, melanoma. More than $2.4 billion is spent annually on therapies, which does not consider the morbidity from disfiguring treatments. Increased exposure to ultraviolet radiation (UVR) from the sun or artificial sources is a primary risk factor and half the lifetime skin damage from UVR overexposure occurs before age 20.

Recently, skin cancer prevention interventions delivered in U.S. primary and middle schools have demonstrated effectiveness. However, there is deficiency in interventions for high school students, whose health behaviors are transitioning from the purview of parents or caretakers. Changes in social norms, risk-taking and the desire for sexual appeal affect this group's UVR exposure patterns and their perceived skin cancer risk. Few studies have addressed sun protection in multiethnic high school students, who underestimate their skin cancer risk.

To address this gap we conducted a pilot study using both qualitative and quasi-experimental designs to investigate whether a school-based intervention entitled, SunSafe In the Middle School Years (SunSafe), could be adapted for use in a multiethnic high school in Honolulu, HI. We used qualitative research methods to incorporate information from discussions with students, parents, teachers and community members to adapt the program. Discussion themes provided strategies that were integrated into the existing SunSafe program.

The adapted SunSafe intervention was then delivered to 250, 10th grade students. The curriculum consisted of a 30-minute presentation, modeling of sun protection apparel, and a Q&A component. Branded resources were created and included a UVR-sensitive wristband that changed color to provide a visible cue of students' UVR exposure levels. A quasi-experimental pretest/posttest design was used to assess changes in students' knowledge, attitudes, and self-reported and observed sun protection behaviors, relative to the intervention's implementation. A 28-item standardized survey assessed students' self-reported sun protection knowledge and attitude changes. A field assessment instrument, the Systematic Observation of Sun Protection Factors, measured observed changes in students' collective use of headwear, sunglasses, protective clothing, and shade.

A total of 208 students provided parental consent and were assented to the study. The students' ethnic distribution was 51.6 % Asian, 30.4% Native Hawaiian/Pacific Islander, 8.4% White, 3.5 % Hispanic, 2.7 % Black, and 3.2% two or more ethnicities. Significant increases were found in students' knowledge, attitudes, and intended sun protection behaviors at posttest, compared to pretest (T-test p &lt; 0.05). One item measuring attitudes toward tanning did not show significant improvement. At baseline, 12.5% of students wore hats, 4% sunglasses, 10.1% had long sleeves, 33.4 % had full lower body coverage, and 67.8% used shade. At 12 months, 13.1% used hats, 1.9% sunglasses, 16.3% had long sleeves, 39.4% had full lower body coverage, and 81% used shade.

Our pilot study found it feasible to adapt SunSafe in Middle School Years for multiethnic high schools students at risk for UVR overexposures and skin cancer. Lack of improvement in attitudes towards tanning may have been biased by students' self-perceptions regarding their own skin tone, with 90-80% having medium or darker complexions. Further investigations are needed to assess the active components of the adapted SunSafe program, the possible geographic differences in the program's utility and the role of skin complexion in attitudes towards tanning and sun exposure in multiethnic students.

Citation Format: Kevin Cassel, Anh Tran, Lynn Murakami-Akasuka, Jodi Tanabe-Hanzawa, Terrilea Burnett, Christopher Lum. Adapting SunSafe: A skin cancer prevention intervention for use with multiethnic high school students. [abstract]. In: Proceedings of the Eighth AACR Conference on The Science of Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; Nov 13-16, 2015; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2016;25(3 Suppl):Abstract nr B56.

PIK3CA Somatic Mutation Status in Relation to Patient and Tumor Factors in Racial/Ethnic Minorities with Colorectal Cancer

BACKGROUND

Approximately 10% to 20% of colorectal cancers exhibit somatic mutations in the phosphoinositide-3-kinase, catalytic, alpha polypeptide gene (PIK3CA). We evaluated the relationship of PIK3CA mutation status in colorectal cancer with race/ethnicity, colorectal cancer survival, and other patient and tumor factors.

METHODS

This study comprised 377 racial/ethnic minorities with incident invasive colorectal cancer, enrolled in the Colon Cancer Family Registry via population-based cancer registries. Tumor specimens were tested for PIK3CA mutations in exon 9 and 20 hotspots, BRAF p.V600E mutations, and DNA mismatch repair (MMR). In logistic regression models, we evaluated the association between PIK3CA mutation status and race/ethnicity, overall, and by mutation site. Using Cox regression, we evaluated the association between PIK3CA mutation status and survival after colorectal cancer diagnosis.

RESULTS

PIK3CA mutations were detected in 42 cases (11%), with a similar prevalence across racial/ethnic groups. Individuals with PIK3CA-mutated colorectal cancer were significantly more likely than those with PIK3CA-wildtype disease to have proximal colon cancer, MMR-deficient tumors, and a germline MMR mutation (P ≤ 0.01). There was no evidence for an association between PIK3CA and overall survival (HR, 0.77; 95% confidence interval, 0.43-1.39).

CONCLUSIONS

The prevalence of PIK3CA mutation status in colorectal cancer does not differ according to race/ethnicity, but may vary according to other relevant clinicopathologic and etiologic factors, including germline MMR mutation status, tumor MMR status, and tumor site.

IMPACT

These findings underscore the importance of PIK3CA mutation status in colorectal cancer epidemiology and provide evidence that the prevalence of such mutations is similar across several racial/ethnic groups.

Risk of colorectal cancer for carriers of mutations in MUTYH, with and without a family history of cancer

We studied 2332 individuals with monoallelic mutations in MUTYH among 9504 relatives of 264 colorectal cancer (CRC) cases with a MUTYH mutation. We estimated CRC risks through 70 years of age of 7.2% for male carriers of monoallelic mutations (95% confidence interval [CI], 4.6%-11.3%) and 5.6% for female carriers of monoallelic mutations (95% CI, 3.6%-8.8%), irrespective of family history. For monoallelic MUTYH mutation carriers with a first-degree relative with CRC diagnosed by 50 years of age who does not have the MUTYH mutation, risks of CRC were 12.5% for men (95% CI, 8.6%-17.7%) and 10% for women (95% CI, 6.7%-14.4%). Risks of CRC for carriers of monoallelic mutations in MUTYH with a first-degree relative with CRC are sufficiently high to warrant more intensive screening than for the general population.

Genetic variation in the inflammation and innate immunity pathways and colorectal cancer risk

BACKGROUND

It is widely accepted that chronic inflammation plays a role in the etiology of colorectal cancer. Using a two-stage design, we examined the associations between colorectal cancer and common variation in 37 key genes in the inflammation and innate immunity pathways.

METHODS

In the discovery stage, 2,322 discordant sibships (2,535 cases, 3,915 sibling controls) from the Colorectal Cancer Family Registry were genotyped for more than 600 tagSNPs and 99 single-nucleotide polymorphisms (SNP) were selected for further examination based on strength of association. In the second stage, 351 SNPs tagging gene regions covered by the 99 SNPs were tested in 4,783 Multiethnic Cohort subjects (2,153 cases, 2,630 controls).

RESULTS

The association between rs9858822 in the PPARG gene and colorectal cancer was statistically significant at the end of the second stage (OR per allele = 1.36, Bonferroni-adjusted P = 0.045), based on the "effective" number of markers in stage II (n = 306). The risk allele C was common (frequency 0.3) in African Americans but rare (frequency < 0.03) in whites, Japanese Americans, Latinos, and Native Hawaiians. No statistically significant heterogeneity of effects across race/ethnicity, body mass index (BMI) levels, regular aspirin use, or pack-years of smoking was detected for this SNP. Suggestive associations were also observed for several SNPs in close vicinity to rs9858822.

CONCLUSIONS

Our results provide new evidence of association between PPARG variants and colorectal cancer risk.

IMPACT

Further replication in independent samples is warranted.

Fine-mapping of genome-wide association study-identified risk loci for colorectal cancer in African Americans

Genome-wide association studies of colorectal cancer (CRC) in Europeans and Asians have identified 21 risk susceptibility regions [29 index single-nucleotide polymorphisms (SNPs)]. Characterizing these risk regions in diverse racial groups with different linkage disequilibrium (LD) structure can help localize causal variants. We examined associations between CRC and all 29 index SNPs in 6597 African Americans (1894 cases and 4703 controls). Nine SNPs in eight regions (5q31.1, 6q26-q27, 8q23.3, 8q24.21, 11q13.4, 15q13.3, 18q21.1 and 20p12.3) formally replicated in our data with one-sided P-values <0.05 and the same risk directions as reported previously. We performed fine-mapping of the 21 risk regions (including 250 kb on both sides of the index SNPs) using genotyped and imputed markers at the density of the 1000 Genomes Project to search for additional or more predictive risk markers. Among the SNPs correlated with the index variants, two markers, rs12759486 (or rs7547751, a putative functional variant in perfect LD with it) in 1q41 and rs7252505 in 19q13.1, were more strongly and statistically significantly associated with CRC (P < 0.0006). The average per allele risk was improved using the replicated index variants and the two new markers (odds ratio = 1.14, P = 6.5 × 10(-16)) in African Americans, compared with using all index SNPs (odds ratio = 1.07, P = 3.4 × 10(-10)). The contribution of the two new risk SNPs to CRC heritability was estimated to be 1.5% in African Americans. This study highlights the importance of fine-mapping in diverse populations.

Implications of generating genetic test results for colon cancer in the international, population-based colon cancer family registry

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Background: The ability to genotype large numbers of people rapidly and inexpensively for research purposes highlights the need to develop guidelines for providing medically-relevant research results - including unanticipated findings - to study participants. The Colon Cancer Family Registry (C-CFR) is the oldest and largest international colon cancer population-based registry; its experience managing genetic research findings can offer guidance to clinicians and researchers. The C-CFR has enrolled 10,019 cases with colon cancer and 24,708 family members in six registries in the US, Canada, Australia, and New Zealand. Deleterious (“high risk”) germline mutations have been identified in DNA mismatch repair (MMR) genes (MLH1, MSH2, MSH6, PMS2) and the MutYH gene. The aims of this presentation are to: (1) report the uptake of genetic test results by C-CFR participants; (2) systematically compare disclosure protocols and barriers to uptake by registry; (3) make recommendations to guide clinicians and researchers. Methods: Uptake of genetic test results was calculated from data collected by the C-CFR; key investigators (KIs) from each registry completed a survey about disclosure decision-making; KIs also took part in discussions to generate recommendations. Results: Registry-wide molecular testing has identified deleterious MMR germline mutations for at least one member of 424 families (4%) and 48 biallelic MutYH gene carriers. Uptake of test results ranged from 56-86% (n= 1542) across registries. Barriers to disclosure include: (1) lack of pre-existing notification protocols; (2) logistics of re-consent; (3) limited involvement of genetic counselors at some registries; (4) in the US, the requirement that genetic testing be performed in a CLIA approved laboratory; (5) IRBs declining approval; and (6) budget constraints. Conclusions: Based on our international registry’s findings we recommend that researchers generating genetic information establish plans for disclosure at the outset; obtain subject consent a priori; consider subject knowledge and disclosure preferences; provide guidance and budget for clinical follow-up; and involve genetic counselors.

Cancer risks for monoallelic MUTYH mutation carriers with a family history of colorectal cancer

Cancer risks for a person who has inherited a MUTYH mutation from only one parent (monoallelic mutation carrier) are uncertain. Using the Colon Cancer Family Registry and Newfoundland Familial Colon Cancer Registry, we identified 2,179 first- and second-degree relatives of 144 incident colorectal cancer (CRC) cases who were monoallelic or biallelic mutation carriers ascertained by sampling population complete cancer registries in the United States, Canada and Australia. Using Cox regression weighted to adjust for sampling on family history, we estimated that the country-, age- and sex-specific standardized incidence ratios (SIRs) for monoallelic mutation carriers, compared to the general population, were: 2.04 (95% confidence interval, CI 1.56-2.70; p < 0.001) for CRC, 3.24 (95%CI 2.18-4.98; p < 0.001) for gastric cancer, 3.09 (95%CI 1.07-12.25; p = 0.07) for liver cancer and 2.33 (95%CI 1.18-5.08; p = 0.02) for endometrial cancer. Age-specific cumulative risks to age 70 years, estimated using the SIRs and US population incidences, were: for CRC, 6% (95%CI 5-8%) for men and 4% (95%CI 3-6%) for women; for gastric cancer, 2% (95%CI 1-3%) for men and 0.7% (95%CI 0.5-1%) for women; for liver cancer, 1% (95%CI 0.3-3%) for men and 0.3% (95%CI 0.1-1%) for women and for endometrial cancer, 4% (95%CI 2-8%). There was no evidence of increased risks for cancers of the brain, pancreas, kidney, lung, breast or prostate. Monoallelic MUTYH mutation carriers with a family history of CRC, such as those identified from screening multiple-case CRC families, are at increased risk of colorectal, gastric, endometrial and possibly liver cancers.

Accuracy of colorectal polyp self-reports: findings from the colon cancer family registry

INTRODUCTION

Colorectal adenomas and other types of polyps are commonly used as end points or risk factors in epidemiologic studies. However, it is not known how accurately patients are able to self-report the presence or absence of adenomas following colonoscopy.

METHODS

Participants in the Colon Cancer Family Registry provided self-reports of recent colorectal cancer (CRC) screening activity, and whether or not they had ever been told they had a polyp. Positive and negative predictive values for polyp self-report were calculated by comparing medical records with self-reports from 488 participants.

RESULTS

The positive predictive value for self-reported polyp was 80.9%, and the negative predictive value was 85.8%. The predictive values did not differ by age group or sex, but participants with a previous diagnosis of CRC had a lower negative predictive value (76.2%) than participants with no personal history of CRC (89.0%; P = 0.04).

CONCLUSIONS

Predictive values for self-reports of polyps are fairly high, but researchers needing accurate polyp data should obtain medical record confirmation. Pursuing medical records on only those participants self-reporting a polyp could result in an underestimation of the polyp prevalence in a study population.

Residues of spinosad in the tissues of sheep after aerosol treatment of blowfly myiasis

OBJECTIVE

To measure the residues of spinosad and chlorhexidine in the tissues of sheep after treatment of blowfly strike.

PROCEDURE

Fourteen sheep with natural myiasis and 12 with artificial infestations of Lucilia cuprina larvae had the wool removed over their infestations and were treated with an aerosol wound dressing containing spinosad and chlorhexidine. Sheep were killed up to 14 days after treatment and residues of the chemicals measured in tissues.

RESULTS

Chlorhexidine was not detected in any tissue. Residues of spinosad were highest in fat, lowest in muscle and intermediate in liver and kidney. The highest residue detected was 0.2 mg/kg spinosad in perirenal fat 7 days after generous treatment of a sheep with a large fly strike. Residues of spinosad in fat peaked 3 to 7 days after treatment and 1 to 3 days after treatment in liver and kidney.

CONCLUSION

These studies present a realistic worst-case in struck sheep and at the highest dose studied, equivalent to 5.8 mg spinosad per kg body weight, the maximum residue detected of 0.2 mg/kg in peri-renal fat was 20% of the Australian maximum residue limit. Muscle, liver and kidney residues of spinosad were also below the Australian maximum residue limits at all times.

The role of nitric oxide in neoplastic transformation of C3H 10T1/2 embryonic fibroblasts

Nitric oxide synthase inhibitors block the neoplastic transformation of C3H 10T1/2 cells in vitro. Evidence presented herein suggests that they mediate their effects early in the carcinogenic process as brief treatment with the NOS inhibitor aminoguanidine (AG) during log phase cell growth (initiation phase) is sufficient to block foci formation. In contrast, treatment initiated after formation of a confluent monolayer was associated with diminished protection, while treatment commencing late in the promotional phase had no protective effect and appeared to enhance the number and stage of foci observed. These findings suggest that while AG treatment can inhibit transformation during the early promotional phase, it most effectively inhibits transformation during the initiation phase. In general AG enhanced growth of both normal and tumor cells, suggesting that effects on growth were unrelated to its anti-transformation properties, however, these effects could be related to the effect on tumor cell stage noted above. Although induction of inducible nitric oxide synthase (iNOS) by treatment with LI during the last 2 weeks of the assay was associated with enhanced transformation, the efficacy of AG in protecting against transformation was not clearly associated with substantial reductions in NO synthesis. The data suggest that AG inhibits transformation early in the transformation process independently of iNOS inhibition and that AG may have deleterious effects late in the process, possibly through stimulation of tumor cell growth.

Biological models of two acarine predators of the grain mite, Acarus siro L

A biological model of predation was developed using granular food held in closely packed screen trays to propagate the grain mite, Acarus Siro L., and two of its predators, Blattisocius dentriticus (Berl.) and Cheyletus eruditus (Schrank). Both predators limited prey abundance. Cannibalism among predators, particularly C. eruditus, was an important factor in ensuring the survival of the prey and predator populations. Cheyletus eruditus eliminated B. dentriticus when the two species were propagated in the same experimental universe. Cyclicity and dispersion of the interacting species appeared to result more from the initial age structure and from dispersion of the prey than from predator attack. A population model was used to assess the relative importance of the population components of A. siro and C. eruditus in the simplified predator–prey interactions.

Prey consumption in acarine predator-prey populations reared in the greenhouse

Two factors, in addition to temperature, could affect the assessment of Amblyseius fallacis as a natural enemy of Tetranychus urticae infesting alfalfa. These are initial prey density and sampling of the predator–prey populations during daylight hours. The influence of these factors was determined by propagating predator–prey populations having different initial prey densities on alfalfa in the greenhouse, recording the subsequent variation in the numbers of the two species during daylight hours, and comparing estimates of the rates at which prey entered and were removed from the populations. A. fallacis was able to reduce prey density before webbing of the alfalfa plants occurred. Prey consumption by the predator populations was judged capable of inducing the observed decline in prey numbers.

Effect of temperature on a greenhouse acarine predator–prey population

Populations of the two-spotted mite, Tetranychus urticae, and its acarine predator, Amblyseius fallacis, were propagated on alfalfa in the greenhouse at constant temperatures in the range 65 to 85 °F (18.3–29.4 °C). The predator limited the initial increase in prey abundance only at temperatures above about 70 °F (21.1 °C). At 80 and 85 °F (26.7 and 29.4 °C) fluctuations in prey and predator numbers increased in amplitude as propagation continued. The age structure of the predator population reared at 75 °F (23.9 °C) differed from that of populations propagated at the other temperatures.

ASPECTS OF THE INTERACTION BETWEEN A CHALCID PARASITE AND ITS ALEURODID HOST

Three populations of the greenhouse whitefly, Trialeurodes vaporariorum, and its chalcid parasite Encarsia formosa were propagated each year for three consecutive years on tomato plants in the greenhouse. The abundance of the host and parasite species fluctuated either with peaks of increasing amplitude, with peaks of decreasing amplitude, or with irregular peaks. The dominant process in the interaction was the occurrence of two qualitatively different types of host larval mortality: (a) parasitization, and (b) almost immediate killing after attack by adult parasites. Fluctuations in host and parasite abundance resulted from the almost immediate killing of small host larvae and the death of the short-lived adult parasites. The parasite population tended to destroy similar percentages of host populations of different densities but host mortality was also related to the age structure of the host population. Variation in host reproduction, caused by differences in rearing temperature and by seasonal variation in the physical environment, influenced host and parasite densities.

HOST LARVAL MORTALITY IN AN EXPERIMENTAL HOST–PARASITE POPULATION

Two populations of Trialeurodes vaporariorum (Westw.) and its chalcid parasite Encarsia formosa Gahan were reared on tomato plants in the greenhouse at 72–76 °F for 26 weeks. Although the abundance of both species fluctuated with peaks of increasing amplitude, the population that was initially larger remained so throughout the period of sampling because the parasite inflicted similar rates of mortality in both cases. The fluctuations of the two separate populations were synchronized throughout the period of propagation. Host mortality, which resulted either from almost immediate killing of host scales following attack by adult parasites or from death of host larvae following parasitization and development of parasite progeny, was determined by parasite density, host size, and possibly by a number of other factors such as the age structure of host larval populations, age of adult parasites, and succulence of leaves on which the host larvae developed. The interaction of host and parasite produced cycles in the age structures of host and parasite populations that, in turn, influenced the interaction of the two species. The death of host larvae following attack by adult parasites was a form of host protection, as it ensured the rapid decline in the abundance of the parasite population and was, therefore, the primary factor in the maintenance of the host–parasite system.

AN ACARINE PREDATOR–PREY POPULATION INFESTING STORED PRODUCTS

Populations of the stored product mite Tyrophagus putrescentiae (Schrank) and its predator Blattisocius dentriticus (Berl.) were propagated in two experimental universes. Although the predator determined the size of the prey populations, the densities of both species fluctuated with peaks of abundance occurring every 6 to 8 weeks. A number of factors modified, to some extent, the role of "predator searching" as a mechanism controlling both the average densities and fluctuations in abundance of the two species. With large fluctuations in the abundance of the prey there was a pronounced cycle in the age structure of the predator and prey populations. The larger stages of the prey were largely immune to attack by the predator. Individuals of the predator developed to about one-half their normal size when the prey were scarce. The combination of immune stages of the prey and adjustment of predators to scarcity of prey ensured the coexistence of the predator–prey system. Contamination of experimental populations by psocids was one of the major hazards in rearing the populations for extended periods.